CNC turning machine

Abstract

A turning machine is characterized by a new and improved control and mechanism for positioning the turning tool on the head. A cnc control issues command signals for selectively positioning the tool on the head. These signals are developed from an encoder which provides the instantaneous position of the rotating part being turned and from a program in the cnc containing information about the part. A closed loop control system receives these command signals and converts same into a control current for a linear motor which is the prime mover controlling the positioning of the tool on the head. The linear motor operates a carriage on the head and the cutting tool mounts on the carriage opposite the connection of the linear motor to the carriage. The carriage is a hollow bar guided on the head by sets of rollers which are cooperatively arranged to provide yieldably forceful constraint of the bar. The rolling action of the bar on the head provides a low friction, low inertia construction enabling rapid response to cnc commands. The head also contains various sensors providing position and velocity feedback information for use by the closed loop control. The closed loop control contains various circuit components organized and arranged to provide fast and faithful response to command signals. The machine has the ability to accurately turn complex parts where position information is being rapidly updated, often in the tens of kilohertz frequency range. Different parts can be turned by merely changing the cnc program.

The questions raised in reexamination request No. 90/001,657, filed Dec. 1, 1988, have been considered and the results thereof are reflected in this reissue patent which constitutes the reexamination certificate required by 35 U.S.C. 307 as provided in 37 CFR 1.570(e).

Description

or the feed directionor scale reference system techniques used in electronic and servomechanism design.

When switch 450 is in the position which couples the output of summing junction 422 to the input of summing junction 466, the control assumes the position control mode of operation and it is this mode which is used during precision turning operations on a part.

From consideration of the foregoing description and the drawings, it will be further appreciated that in the position control mode of operation, the minor feedback loop providing velocity feedback is also active to modify the position error signal. This modification occurs at summing junction 466 and creates an error signal input to amplifier 468 which in turn acts upon power supply 332 to effect corresponding control of linear motor 72.

During an operating sequence on a part, the position control mode of operation may be active for only a portion of the time. A typical operating sequence involves the carriage advancing from a home, or retracted, position toward a part with the actual turning operations being allowed to commence only after the cutting tool has been brought into close proximity with the part.

Over the range of carriage advance from the home position to a position just off the part, the control operates in the velocity control mode where only the velocity feedback loop is active.

In the velocity control mode, switch 450 is operated to conduct a demand velocity signal received from the CNC and converted into an analog signal by a DAC 470 to summing junction 466. The demand velocity is set by the particular part program. The part program also sets the cutting start position register with data representing offset, or the point at which the position control mode of operation is to commence.

As the tool and carriage advance toward the part while the control is in the velocity control mode of operation, the reference marker is issued by position sensor 74 to set the absolute reference point into the control. The velocity control mode will continue until the offset, if any, has been tranversed.

Once the offset has been traversed, the position control mode begins at which time the up/down cutting counter 446 becomes active, and the contacts 450 are switched to conduct the signal from summing junction 422, instead of the signal from DAC 470, to summing junction 466.

The position data received from the CNC control and acted upon by control 80 causes input position commands to be issued to effect the closed loop position control of linear motor 72 and hence of the carriage and tool. In this regard the position commands are correlated with the rotation of the piston as provided by position encoder 54, and therefore the tool is caused to follow a path such as described above for example with reference to FIG. 4 where in turning an elliptical contour the carriage is caused to execute two oscillations per each revolution of the piston. The control operates to ensure the faithful correspondence of the cutting tool to the demand position so that the desired contour is imparted to the piston skirt. The process continues until the program has been executed at which time the carriage can be retracted to the home position.

The turning operations are conducted with efficiency and accuracy. The interaction between the control electronics and the mechanical mechanism achieves a response which enables the tool tip to closely track the desired contour to be created in the part while the part is rotating at relatively high speed. Moreover, this is accomplished without undesired deflections, tool chatter or like impediments to the machine's performance, and the mechanical construction of the head in conjunction with the linear motor are especially advantageous in enabling this outstanding performance to be attained.

While the advantageous aspects of the invention are most readily apparent when the tool is performing the finish operations because this is where the final accuracy is imparted to the piston, the invention can be used to conduct operations other than finish turning. For example, by appropriate programming of the CNC it is possible for the tool to conduct semifinish turning, grooving, and other related operations, in addition to finish turning. Therefore, a turning machine embodying principles of the invention is adapted to conduct all the necessary operations which are required in turning of a part such as a piston. Because these operations may be defined mathematically by the computer program entered into the CNC, significant accuracies and improvements in efficiencies result while at the same time the machine is endowed with versatility to produce parts of different geometrical requirements without any significant changeover.

The CNC is a conventional apparatus which is programmed in a conventional manner to cause the control to execute the above defined functions. In this regard conventional programming techniques are employed to create an operating program based on knowledge of the part geometry and the organization and arrangement of the turning apparatus. The CNC can perform the necessary calculations on a realtime basis to provide signals via high speed data link 82 to control 80. For example as noted above, 14,400 hertz may be a typical frequency of position data transmission, and for the typical geometries involved, the mechanism can faithfully follow inputs at this rate.

A turning machine embodying principles of the invention exhibits a performance which enables the cutting tool to follow, with quickness and accuracy, changes which are correlated with the rapidly rotating part being turned. Depending upon the actual profile of a part, any given updating from the CNC may or may not contain a change in position information. For example, in the case where a circular shape is to be created in conjunction with an axial taper, the radial position of the cutting tool would change at most only once per revolution of the piston, and therefore the updating of the demand position would actually change at most only once per revolution of the part.

The versatility of the invention should be readily apparent. I order to change the machine to turn a different piston shape, all that is necessary is to load the CNC with a new program relating to the new piston geometry. The CNC will act upon the program in conjunction with the feedback signal from encoder 54 to provide appropriate command signals for the radial positioning of the cutting tool. The closed loop control as disclosed with reference to FIGS. 12A, 12B, and 12C comprises means for enabling the tool to faithfully follow the commands.

It will also be observed that the mechanical construction of the turning machine has the advantage of being relatively compact, yet possessing strength to conduct the turning operations in conjunction with the ability to respond quickly to even small changes.

Based upon the foregoing description, it will be appreciated that details of the turning machine construction can be specified in accordance with conventional engineering design and fabrication procedures. For example the characteristics of the leaf spring mechanism are chosen to provide for the forceful constraint of the bar in the assembled condition of the machine as illustrated with reference to FIGS. 8, 9, and 10. The amount of force which is exerted is sufficient to prevent undesired deflections at all times, even tool chatter when the tool is operating on a workpiece in the usual manner. The extent of the yieldable forceful constraint is however insufficient to detract in any significant way from the ability of the carriage to roll fully on the sets of rollers. Although the engagement of the rollers with the bar is described as being yieldably forceful, the typical usage of the turning machine under the intended operating conditions does not result in yielding of the rollers.

It is also to be observed that the action of the rollers on the carriage is symmetrical so that no undesired bending loads are created in the carriage by virtue of the yieldably forceful action of the rollers upon it. By utilizing a bar of rectangular cross section for the carriage and two sets of orthogonally related (90° apart) rollers acting upon the opposite parallel surfaces of the bar, the bar is accurately guided for straight line motion. With the adjustment feature provided for each of the two orthogonally related sets of rollers as described above, the line of travel can be accurately set in both a vertical plane as well as a horizontal one.

It should also be observed that the rollers alone serve to guide and constrain the moving parts. In other words there is no guide means which is directly active on the armature of the linear motor.

The invention comprises a significant development in turning apparatus, and while a preferred embodiment has been disclosed, it will be appreciated that principles are applicable to other embodiments.

Claims

1. In a turning machine (40) comprising means for rotating (48) a part (42) about an axis (44) and for causing a cutting tool (56) to make an axial pass along the part while the radial position of the tool relative to the part is selectively controlled in correlation with the angular position of the part about the axis of rotation as the part is being rotated, the improvement which comprises a main cnc control (58), angular position sensing means (54) operatively coupled with said means for rotating the part to provide to the cnc control information representative of instantaneous angular position of the part about the axis for rotation as the part is being rotated, radial position sensing means (74) for sensing the radial position of the cutting tool relative to the part, radial velocity sensing means (76) for sensing the radial velocity of the tool relative to the part, and a closed loop control system (80) for closed loop controlling the radial position of the cutting tool relative to the part as a function of the radial position of the cutting tool and the radial velocity of the cutting tool, said closed loop control system comprising an electric linear motor (72) as the prime mover for radially positioning the cutting tool, said cnc comprising means for issuing commands to the closed loop control system correlated with the information with said position sensing means and information about the part, and said closed loop control system comprising means for converting the cnc commands into a corresponding control current for the linear motor wherein one end of an elongated carriage is adapted to be coupled to the cutting tool, the other end of the carriage being coupled to the motor for transmitting linear motion and wherein said linear motor and carriage are mounted on the head of the machine, and in which said carriage is guided for reciprocable linear motion on the machine head by guide means (138,178) disposed in cooperative relation with the carriage and the machine head for facilitating sliding movement of the carriage, and spring means (148) for spring-loading the guide means with a spring force sufficient to resist displacement in any direction transverse to the radial direction and thereby minimize deflection of the carriage in any such direction.

2. The improvement set forth in claim 1 in which said linear motor comprises a linearly moveable armature containing a coil disposed within a magnetic field and said control current being oonducted conducted through said coil to control the linear positioning of said armature.

3. The improvement set forth in claim 2 in which the magnetic field within which said coil is disposed comprises means, including a circular annular magnet, defining an annular free space within which flux issued by the magnet is contained, and said coil is concentrically disposed within said free space.

4. The improvement set forth in claim 3 2 in which said armature is in the form of a bobbin which in turn is operatively connected to a the carriage on which the cutting tool is mounted.

5. The improvement set forth in claim 4 in which said linear motor and carriage are mounted on a head of the machine, and in which said carriage is guided for the linear motion on the machine head by means of guide means, said bobbin being free of contact with said guide

means. 6. The improvement set forth in claim 5 1 in which said guide means comprises plural rollers acting upon

said carriage. 7. The improvement set forth in claim 6 in which said carriage comprises a hollow bar having an exterior surface which in transverse cross section is polygonal, and in which there are plural sets of rollers having rolling contact with the exterior surface of said hollow

bar. 8. The improvement set forth in claim 7 in which at least one set of rollers comprises plural non-yieldably mounted rollers and plural yieldably mounted rollers, such yieldably and non-yieldably mounted rollers coacting on respective exterior surface portions of said hollow bar to provide for yieldably forceful constraint of said hollow bar by such rollers while still allowing the carriage to be rolled on said

rollers. 9. The improvement set forth in claim 8 in which said bar's exterior cross sectional shape is rectangular and there are two sets of rollers, orthogonally related, each set co-acting on respective opposite exterior surface portions of said bar, and in which the non-yieldably mounted rollers of each set comprise a forward pair and a rearward pair having rolling contact with said bar at spaced apart points and the yieldably mounted rollers of each set comprise a forward pair and a rearward pair having rolling contact with said bar at substantially the same forward and rearward locations as for the coacting non-yieldably mounted ones, the yieldably mounted roller pairs each being mounted on the machine head by means of a corresponding leaf spring mechanism, and further including means for selectively positioning at least one pair of each set's non-yieldably mounted rollers toward and away from the axis of the hollow bar.

10. The improvement set forth in claim 1 in which the linear motor is mounted on a head of the turning machine and is operatively connected to a carriage on which the cutting tool is mounted, and said closed loop control system including plural sensors on the machine's head operated by movement imparted to said carriage by said linear motor, said sensors providing respective signals for use by the closed loop control system.

11. The improvement set forth in claim 10 in which one of said plural sensors provides a velocity signal representative of instantaneous velocity of said carriage and another of said plural sensors provides a position signal of instantaneous position of said carriage.

12. The improvement set forth in claim 11 in which said one sensor comprises a sensing coil concentric with said linear motor and disposed within a bore passing through the interior of the linear motor, said one sensor further including a core concentrically disposed with respect to said sensing coil and moveable through the sensing coil with the operation of the carriage by the linear motor so that the sensing coil provides a signal indicative of the instantaneous velocity of the

carriage. 13. The improvement set forth in claim 11 in which said another sensor comprises In a turning machine (40) comprising means for rotating (48) a part (42) about an axis (44) and for causing a cutting tool (56) to make an axial pass along the part while the radial position of the tool relative to the part is selectively controlled in correlation with the angular position of the part about the axis of rotation as the part is being rotated, the improvement which comprises a main cnc control (58), angular position sensing means (54) operatively coupled with said means for rotating the part to provide to the cnc control information representative of instantaneous angular position of the part about the axis for rotation as the part is being rotated, radial position sensing means (74) for sensing the radial position of the cutting tool relative to the part, radial velocity sensing means (76) for sensing the radial velocity of the tool relative to the part, and a closed loop control system (80) for closed loop controlling the radial position of the cutting tool relative to the part as a function of the radial position of the cutting tool and the radial velocity of the cutting tool, said closed loop control system comprising an electric linear motor (72) as the prime mover for radially positioning the cutting tool, said cnc comprising means for issuing commands to the closed loop control system correlated with the information with said position sensing means and information about the part, and said closed loop control system comprising means for converting the cnc commands into a corresponding control current for the linear motor in which the linear motor is mounted on a head of the turning machine and is operatively connected to a carriage on which the cutting tool is mounted, and said closed loop control system including at least one sensor on the machine's head operated by movement imparted to said carriage by said linear motor, said at least one sensor providing a signal for use by the closed loop control system, the at least one sensor comprising a fixed reference scale (220) in the form of a grating mounted on the carriage for movement therewith and a sensing head (222) mounted on the machine's head laterally adjacent the line of travel of the scale, the motion of the scale past said sensing head causing said sensing head to provide the position signal correlating the position of the scale, and hence the carriage, on

the machine's head. 14. The improvement set forth in claim 13 in which the closed loop control system includes plural sensors, a further of said plural sensors senses when said scale is in juxtaposition to said sensing head to thereby define a range over which said sensing

head is confined to provide said position feedback signal. 15. The improvement set forth in claim 1 In a turning machine (40) comprising means for rotating (48) a part (42) about an axis (44) and for causing a cutting tool (56) to make an axial pass along the part while the radial position of the tool relative to the part is selectively controlled in correlation with the angular position of the part about the axis of rotation as the part is being rotated, the improvement which comprises a main cnc control (58), angular position sensing means (54) operatively coupled with said means for rotating the part to provide to the cnc control information representative of instantaneous angular position of the part about the axis for rotation as the part is being rotated, radial position sensing means (74) for sensing the radial position of the cutting tool relative to the part, radial velocity sensing means (76) for sensing the radial velocity of the tool relative to the part, and a closed loop control system (80) for closed loop controlling the radial position of the cutting tool relative to the part as a function of the radial position of the cutting tool and the radial velocity of the cutting tool, said closed loop control system comprising an electric linear motor (72) as the prime mover for radially positioning the cutting tool, said cnc comprising means for issuing commands to the closed loop control system correlated with the information with said position sensing means and information about the part, and said closed loop control system comprising means for converting the cnc commands into a corresponding control current for the linear motor, in which the linear motor is mounted on a head of the turning machine and is operatively connected to a carriage on which the cutting tool is mounted, and said closed loop control system comprising a position control loop which exercises principal control over said linear motor in positioning said carriage and also a velocity control loop in which velocity feedback information supplements the principal control provided by the position loop control in which the machine comprises means for causing said closed loop control system to operate selectively in a position control mode in which the position and the velocity control loops are both active and in a velocity control mode in which only the velocity feedback loop, and not the position feedback loop, is active.

16. The improvement set forth in claim 15 in which the machine comprises means for causing said closed loop control system to operate selectively in a position control mode in which the position and the velocity control loops are both active and in a velocity control mode in which only the velocity feedback loop, and not the position feedback

loop, is active. 17. The improvement set forth in claim 16 15 in which the machine comprises means for executing the velocity control mode of operation at the beginning of an operating sequence on a part until the carriage has been advanced from a home position to a position where the cutting tool is just off the part, and thereafter executing the position control mode of operation to conduct

turning operations on the part. 18. The improvement set forth in claim 17 in which said closed loop control system comprises a register which is set to a zero reference when operation switches from the velocity control mode to the position control mode, and including a switch in the position control loop forward of the velocity control loop which is operated concurrent with the setting of said register to the zero reference to

thereby render the position loop active. 19. The improvement set forth in claim 1 In a turning machine (40) comprising means for rotating (48) a part (42) about an axis (44) and for causing a cutting tool (56) to make an axial pass along the part while the radial position of the tool relative to the part is selectively controlled in correlation with the angular position of the part about the axis of rotation as the part is being rotated, the improvement which comprises a main cnc control (58), angular position sensing means (54) operatively coupled with said means for rotating the part to provide to the cnc control information representative of instantaneous angular position of the part about the axis for rotation as the part is being rotated, radial position sensing means (74) for sensing the radial position of the cutting tool relative to the part, radial velocity sensing means (76) for sensing the radial velocity of the tool relative to the part, and a closed loop control system (80) for closed loop controlling the radial position of the cutting tool relative to the part as a function of the radial position of the cutting tool and the radial velocity of the cutting tool, said closed loop control system comprising an electric linear motor (72) as the prime mover for radially positioning the cutting tool, said cnc comprising means for issuing commands to the closed loop control system correlated with the information with said position sensing means and information about the part, and said closed loop control system comprising means for converting the cnc commands into a corresponding control current for the linear motor, in which said closed loop control system comprises position feedback with means to absolutely relate position feedback to the cutting tool position which said closed loop control system further comprises velocity feedback coactive with the position feedback in which said closed loop control system comprises means for applying the transfer function

K_v /sT+1

to the velocity feedback to modify same, and the transfer function

K_p /sT+1

to the position feedback to modify same, and means for summing the two modified feedback signals and subtracting the sum from a demand position amplified K_i x_i at a position summing junction to create a position error signal for the principal control of the tool position wherein T is chosen to satisfy the relationship

T=K_v /K_p

wherein x_i is the demand position, K_i is gain applied to the demand position, K_p is the gain of the position feedback, K_v is the gain of the velocity feedback, and s is the Laplace operator symbol.

20. The improvement set forth in claim 19 in which said closed loop control system further comprises velocity feedback coactive with the position feedback.

21. The improvement set forth in claim 20 in which said closed loop control system comprises means for applying the transfer function

K_v /sT+1

to the velocity feedback to modify same, and the transfer function

K_p /sT+1

to the position feedback to modify same, and means for summing the two modified feedback signals and subtracting the sum from a demand position amplified K_i x_i at a position summing junction to create a position error signal for the principal control of the tool position wherein T is chosen to satisfy the relationship

T=K_v /K_p

wherein x_i is the demand position, K_i is gain applied to the demand position, K_p is the gain of the position feedback, K_v is the gain of the velocity feedback, and s is the Laplace operator

symbol. 22. The improvement set forth in claim 21 19 further including a feed-forward branch forward of said position summing junction, said feed-forward branch comprising means for providing compensation to the demand position to anticipate the size of future

change in demand postion. 23. The improvement set forth in claim 22 in which said closed loop control system comprises means to modify the velocity feedback by gain K_v2 and to apply the last-mentioned modified velocity feedback to a further summing junction at which the position error signal and the last-mentioned modified velocity feedback are processed to created a modified postion error signal which is used to control the linear motor, and wherein the following relationships exist: ##EQU3##

wherein the velocity feedback signal is sx₀. 24. The improvement set forth in claim 19 In a turning machine (40) comprising means for rotating (48) a part (42) about an axis (44) and for causing a cutting tool (56) to make an axial pass along the part while the radial position of the tool relative to the part is selectively controlled in correlation with the angular position of the part about the axis of rotation as the part is being rotated, the improvement which comprises a main cnc control (58), angular position sensing means (54) operatively coupled with said means for rotating the part to provide to the cnc control information representative of instantaneous angular position of the part about the axis for rotation as the part is being rotated, radial position sensing means (74) for sensing the radial position of the cutting tool relative to the part, radial velocity sensing means (76) for sensing the radial velocity of the tool relative to the part, and a closed loop control system (80) for closed loop controlling the radial position of the cutting tool relative to the part as a function of the radial position of the cutting tool and the radial velocity of the cutting tool, said closed loop control system comprising an electric linear motor (72) as the prime mover for radially positioning the cutting tool, said cnc comprising means for issuing commands to the closed loop control system correlated with the information with said position sensing means and information about the part, and said closed loop control system comprising means for converting the cnc commands into a corresponding control current for the linear motor in which said closed loop control system comprises position feedback with means to absolutely relate position feedback to the cutting tool position, in which the position feedback is provided by a fixed reference scale moveable with the tool and a sensing head past which the scale moves when the tool is operated by the linear motor, the motion of the scale past the sensing head causing the sensing head to provide said position feedback, said closed loop control system further comprising an on-scale sensor for confirming when said scale is in juxtaposition to said sensing head to thereby define a range over which said sensing head is confirmed to provide said position feedback and further including a home sensor for sensing a home position of the cutting tool, said machine comprising means for causing said closed loop control system to operate selectively in a position control mode in which said position feedback as confirmed by said on-scale sensor provides position feedback acted upon by the closed loop control system to exercise principal control over the operation of the linear motor and in a velocity control mode in which the velocity feedback alone is acted upon by the closed loop control system to exercise control over operation of the linear motor, and means for causing the velocity control mode of operation to occur between the home position defined by the home sensor and a position defined by a zero reference set in the control relative to an absolute reference set by the position feedback.

In a turning machine comprising means for rotating a part about an axis and for causing a cutting tool to make an axial pass along the part while the radial position of the tool relative to the part is selectively controlled in correlation with the angular position of the part about the axis of rotation as the part is being rotated, the improvement which comprises a main cnc control, position sensing means operatively coupled with said means for rotating the part to provide to the cnc control information representative of instantaneous angular position of the part about the axis of rotation as the part is being rotated, radial position sensing means for sensing the radial position of the cutting tool relative to the part, radial velocity sensing means for sensing the radial velocity of the tool relative to the part, and a closed loop control system for closed loop controlling the radial position of the cutting tool relative to the part as a function of the radial position of the cutting tool and the radial velocity of the cutting tool, said closed loop control system comprising an electric linear motor for radially positioning the cutting tool, said cnc comprising means for issuing commands to the closed loop control system correlated with information from said position sensing means and information about the part, and said closed loop control system comprising means for converting the cnc commands into a corresponding control signal for the linear motor and wherein said tool is mounted on a carriage which is guided by guide means on a head with the carriage being operatively coupled with the linear motor so as to be selectively positionable along a line of travel on the head in accordance with operation of the linear motor by the control signal developed from the cnc commands, said carriage comprising a hollow bar having an exterior surface which in transverse cross section is polygonal and in which said guide means comprises a plural sets of rollers providing rolling contact with the exterior surface of said hollow bar as said hollow bar is operated by said linear motor and in which at least one set of rollers comprises plural non-yieldably mounted rollers and plural yieldably mounted rollers, such yieldably and non-yieldably mounted rollers coacting with respective exterior surface portions of said hollow bar to provide for yieldablr yieldably forceful constraint of the hollow

bar while allowing the bar to be rolled thereon. 26. The improvement set forth in claim 25 in which said bar's exterior cross sectional shape is rectangular and there are two sets of rollers, orthogonally related, each set coacting on respective opposite exterior surface portions of said bar and in which the non-yieldably mounted rollers of each set comprise a forward pair and a rearward pair having rolling contact with said bar at space point parts and the yieldably mounted rollers of each set comprise a forward pair and a rearward pair having rolling contact with said bar at substantially the same forward and rearward locations as for the coacting

non-yieldably mounted ones. 27. The improvement set forth in claim 26 in which the yieldably mounted roller pairs of each set are mounted on the head by means of a corresponding leaf spring mechanism and further including means for selectively positioning at least one pair of each set's non-yieldably mounted rollers toward and away from the axis of the

hollow bar. 28. The improvement set forth in claim 26 in which the rollers are disposed on axles and the rollers roll on margins of said exterior surface portions immediately adjacent edges at which said exterior surface

portions meet. 29. The improvement set forth in claim 25 in which said linear motor comprises a linearly moveable armature coaxial with the axis

of the hollow bar and attached to the hollow bar. 30. The improvement set forth in claim 29 in which said armature comprises a tubular bobbin having a circular annular transverse cross sectional shape and a cap via which the bobbin attaches at an axial end thereof to the hollow bar, and stops on the head disposed for abutment by the cap to define limits of travel

for the carriage and bobbin on the head. 31. The improvement set forth in claim 29 in which said armature comprises a tubular bobbin having an open axial end, said open axial end being disposed within a circular annular free space containing a magnetic field, said bobbin comprising a coil thereon disposed within the magnetic field of said free space, said coil receiving a control current constituting the control signal for the prime mover with the interaction between the magnetic field of said free space and the control current in said coil operates the prime mover, and hence

the carriage. 32. The improvement set forth in claim 25 including plural sensors on said head providing position and velocity information derived from operation of the carriage by the linear motor for used

use by the closed loop control. 33. The improvement set forth in claim 32 in which one of said sensors is a velocity sensor comprising a coil mounted on the head and a core which is moveable with the carriage so as to be selectively positionable with respect to said coil by operation of said linear motor to thereby cause a signal to be created in said coil representative of instantaneous velocity of said carriage and another of said sensors is a position sensor disposed on the head laterally adjacent the carriage, said position sensor comprising a sensing head mounted on the machine's head and a scale attached to the carriage with the scale disposed for travel with the carriage along a line of travel past the sensing head for causing the sensing head to provide

signals containing the position information. 34. In a turning machine having a head on which a tool is selectively positionable toward and away from a workpiece by a prime mover and a carriage, an improved prime mover and carriage combination for selectively positioning the tool on the head characterized by low friction, low inertia, and rapid response to input commands and comprising an electric linear motor forming the prime mover and a bar forming the carriage, said bar having plural exterior surface portions via which the bar rolls on coacting sets of rollers on the head, said coacting sets of rollers being arranged to constrain to the bar to motion along a line of travel toward and away from the part while applying yieldably forceful engagement of the bar, and wherein the bar is further defined to have a rectangular exterior cross sectional shape so that said plural exterior surface portions comprise two pairs of parallel surfaces with the two pairs being 90° apart about the axis of the bar, and in which for each pair of parallel surfaces there is a corresponding coacting set of rollers, each coacting set comprising a set of plural non-yieldably mounted rollers and

a set of plural yieldably mounted rollers. 35. The improved prime mover and carriage combination set forth in claim 34 in which each set of yieldably mounted rollers is yieldably mounted on the head by a leaf

spring mechanism. 36. The improved prime mover and carriage combination set forth in claim 35 in which each set of non-yieldably mounted rollers includes means for selectively positioning at least some of its rollers

toward and away from the axis of the bar. 37. The improved prime mover and carriage combination set forth in claim 36 in which said means for selectively positioning at least some of the rollers of each non-yieldably mounted set toward and away from the axis of the hollow bar comprises a yoke containing such rollers and an adjustment screw mechanism engaging said yoke, said adjustment screw mechanism having a threaded engagement with the head to provide for the selective positioning of the yoke by rotating the adjustment screw mechanism and means for locking the adjustment screw mechanism against further rotation once the desired yoke

positioning has been attained. 38. The improved prime mover and carriage combination set forth in claim 37 in which said yoke comprises a hole, said adjustment screw mechanism having a distal end extending into and

engaging the bottom of said hole. 39. The improved prime mover and carriage combination set forth in claim 35 in which each set of yieldably mounted rollers comprises a forward pair and a rearward pair mounted on their respective yokes, each leaf spring mechanism having opposite ends which attach respectively to the corresponding two yokes, and means for

attaching each leaf spring mechanism centrally thereof to the head. 40. The improved prime mover and carriage combination set forth in claim 39 in which each set of non-yieldably mounted rollers comprises a rearward pair and at least one forward pair, each such last-mentioned forward pair and rearward pair being disposed on respective yokes one of which is fixedly secured on the head and the other of which is selectively positionable toward and away from the axis of the hollow bar and when selectively positioned to a desired position is locked against any further

displacement. 41. The improved prime mover and carriage combination set forth in claim 34 in which said bar is hollow throughout its entire length, said tool being mounted at the forward end of said bar, and a cap at the rearward end of said bar via which the bar attaches to the linear

motor, said linear motor being arranged coaxially with said bar. 42. The improved prime mover and carriage combination set forth in claim 41 including stops on the head disposed for abutment by the cap to define

limits of travel for the carriage on the head. 43. The improved prime mover and carriage combination set forth in claim 41 in which said prime mover comprises an armature in the form of a tubular bobbin which attaches at one axial end thereof to said cap and with the opposite axial end thereof being open, said open axial end being disposed within a circular annular free space containing a magnetic field, and said bobbin comprising a coil thereon disposed within the magnetic field of said free space, said coil being adapted for receiving control current for interaction with the magnetic field of said free space to operate said bar along its line of

travel. 44. The improved prime mover and carriage combination set forth in claim 43 in which the magnetic field of said free space is provided by a tubular magnetic having a circular annular cross sectional shape disposed concentrically around said free space.

45. A method of controlling the radial position of a tool relative to the rotational axis of a workpiece in a turning cperation whrein the surface geometry of the workpiece is defined by a data matrix of axial, angular and radial position coordinates, said method comprising the steps of:

generating an anular position signal representative of the current angular position of the workpiece and an axial position signal representative of the current aaxial position of the tool relative to the workpiece;

correlating the angular and axial position signals with the data matrix to generate a demand control signal as a function of the angular and axial position signals;

generating an actual radial position signal representative of the current radial position of the tool and a radial velocity signal representative of the current radial velocity of the tool;

generating a tool feedback signal having a velocity component derived from the radial velocity signal and a position component derived from the actual radial position signal; and

comparing the demand control signal to the tool feedback signal to produce a tool adjustment signal for controlling the radial position of the tool as both a function tool position and velocity.

46. The method of claim 45 wherein the demand control signal has a first component based on the prior demanded radial position value from the data matrix, and a second component based on the difference of the current demanded radial position value and the prior demanded radial position value.

47. The method of claim 46 wherein the second component is a feed forward signal which is a function of the difference in said values.

48. The method of claim 46 wherein the demand control signal is obtained by summing the first component and the second component.

49. The method of claim 46 wherein the first component is modified by integrating the second component and summing the integral of the second component with the first component.

50. The method of claim 45 wherein the tool feedback signal is obtained by summing the velocity component and the position component.

51. The method of claim 45 comprising the further step of modifying the tool adjustment signal by negative feedback of the radial velocity signal.

52. A system for controlling the radial position of a tool relative to the rotational axis of a workpiece whrein the surface geometry of the workpiece is defined by a data matrix of axial, angular and radial position coordinates, the system comprising:

angular position sensor means (54) for producing an angular position signal representative of the current angular position of the workpiece (42);

axial position sensor means (66) for producing an axial position signal representative of the current axial position of the tool (56) relative to the workpiece;

cnc means (58) for correlating the angular and axial position signals to the data matrix to produce a demanded radial position signal corresponding to the angular and axial position signals;

an electric linear motor coupled to the tool for radial movement of the tool in accordance with a tool control signal;

radial velocity sensor means (76) for producing a velocity signal representative of the radial velocity of the tool;

radial position sensor means (74) for producing an actual radial position signal representative of the current radial position of the tool; and

control means (80) for,

producing a tool feedback signal having a velocity component derived from the radial velocity signal and a position component derived from the actual radial position signal,

producing a demand control signal derived from the demanded radial position signal, and

comparing the demand control signal and the tool feedback signal to produce the tool control signal for controlling the radial position of the tool as

a function of both tool position and velocity.

53. The system of claim 52 wherein the second control means includes demand signal processing means for producing a demand control signal having a first component (404) based on the prior demanded radial position signal, and a second component (412) based on the difference of the current demanded radial position signal and the prior demanded radial position signal.

54. The system of claim 53 wherein the demand signal processing means further includes means (420) for operating on the difference signal to produce a feed forward signal which is a function of the difference signal.

55. The system of claim 53 wherein the demand signal processing means further includes means for summing (422) the first component and the second component to obtain the demand control signal.

56. The system of claim 53 wherein the demand signal processing means includes means for integrating (418) the second component and summing (408) the integral of the second component with the first component to modify the first component.

57. The system of claim 52 wherein the control means includes tool signal processing means for summing (460) the velocity component and the position component to obtain the tool feedback signal.

58. The system of claim 52 wherein the control means further comprises means for modifying the tool adjustment signal by negative feedback (466) of the radial velocity signal.

59. In combination with a machine tool (40) of the type having a spindle (48) for rotating a workpiece (42) to be machined, a cutting head (56), an electric linear motor (72) for moving the cutting head (56) radially relative to the spindle axis (44), control means for producing an output signal for controlling the linear motor to machine the workpiece to have a configuration that is defined by a stored part program, said control means including means (54) for sensing the angular position of said spindle, means (66) for sensing the axial position of said cutting head and means (74) for sensing the radial position of said cutting head, the improvement characterized in that:

said control means includes means (76) for sensing the radial velocity of said cutting head (56) and produces said output signal for controlling said linear motor in response to said angular position sensing means, said axial position sensing means, said radial position sensing means and said radial velocity sensing means.

60. The machine tool of claim 59 wherein the closed loop control system performs the step of comparing a demand control signal which is a function for the programmed position of the cutting head to a feedback signal which is a function of at least the radial position of the cutting head.

61. The machine tool of claim 60 wherein the output signal for controlling the linear motor is a function of the compared signals and the radial velocity of the cutting head.

62. The machine tool of claim 60 wherein the feedback signal is also a function of the radial velocity of the cutting head.

63. The machine tool of claim 62 wherein the closed loop control system develops the feedback signal by a summation (422) of signals based on the radial position and the radial velocity of the cutting head.

64. The machine tool of claim 59 further comprising cnc means (58), cooperative with the closed loop control system, for generating a prgrammed radial position signal based on a correlation of the angular position of the spindle and the axial position of the cutting head, for use in deriving the demand control signal.

65. The machine tool of claim 63 wherein the closed loop control system further includes feed forward signal processing means for producing a demand control signal which is a function of the present programmed radial position signal and the next successive programmed radial position signal.

66. An improved machine tool (40) of the type having a spindle (48) for rotating a workpiece (42) to be machined, a cutting head (56), an electric linear motor (72) for moving the cutting head radially relative to the spindle axis (44) to machine the workpiece to have configuration that is defined by a stored part program, said linear motor being controlled by closed loop control system (80) responsive to the radial position of the cutting head as derived from radial position sensing means (74) and the radial velocity of the cutting head as derived from radial velocity sending means (76), the improvement characterized in that:

the closed loop control system provides an output signal for controlling the linear motor which is a function of the present and the next successive programmed positions of the cutting head.

67. The machine tool of claim 66 wherein the closed loop control system develops a feed forward signal which is a function of the difference of the present and the next successive programmed positions of the cutting head.

68. The machine tool of claim 67 wherein the feed forward signal is combined with a signal representative of the present programmed position to develop a demand control signal.

69. The machine tool of claim 68 wherein the output signal for controlling the linear motor is a function of the demand control signal, the radial position of the cutting head and the radial velocity of the cutting head.

70. In combination with a machine tool (40) of the type including a spindle (48) for rotating a workpiece (42) to be machined about a spindle axis (44), a cutting head (56), an electric linear motor (72) responsive to a control signal for moving the cutting head (56) radially relative to said spindle axis (44), and control means (80, 58, 54, 66, 74) for providing a control signal to the electric linear motor to machine the workpiece to have a configuration defined by a stored part program, said control means including angular position sensing means (54) for sensing the angular position of the workpiece (42) about the spindle axis (44), axial position sensing means (66) for sensing the axial position of the cutting head (56) along the spindle axis (44), and radial position sensing means (74) for sensing the radial position of said cutting head (56) relative to said spindle axis (44) to develop the control signal as a function of the sensed angular, axial and radial positions, the improvement characterized in that:

the control means further comprises radial velocity sensing means (76) to sense the radial velocity of the cutting head (56) relative to said spindle axis (44) to develop an improved control signal as a function of the sensed angular, axial and radial positions and the sensed radial velocity.

71. The invention of claim 70 wherein the control means develops the control signal from a comparison of a demand control signal derived from the sensed angular and axial positions to a feedback signal derived from the sensed radial position and the sensed radial velocity.

72. The invention of claim 71 wherein the control means includes cnc means (58) for correlating the sensed angular and axial positions to a programmed position which is functionally related to the demand control signal.

73. The invention of claim 71 wherein the control means derives the feedback signal from a summation (422) of signals based on the sensed radial position and the sensed radial velocity.

74. The invention of claim 71 wherein the control means further includes feed forward signal processing means for producing a demand control signal which is a function of the present programmed position and the next

successive programmed position. 75. In a turning machine having a head on which a tool is selectively positionable toward and away from a workpiece by a prime mover and a carriage, an improved prime mover and carriage combination for selectively positioning the tool on the head characterized by low friction, low inertia, and rapid response to input commands and comprising an electric linear motor forming the prime mover wherein one end of the carriage is adapted to be coupled to the cutting tool, the other end of the carriage is coupled to the motor for transmitting linear motion and wherein said linear motor and carriage are mounted on the head of the machine, and in which said carriage is guided for reciprocable linear motion on the machine head by guide means (138,178) disposed in cooperative relation with the carriage and the machine head for facilitating sliding movement of the carriage, and spring means (148) for spring-loading the guide means with a spring force sufficient to resist displacement in any direction transverse to the radial direction and thereby minimize deflection of the carriage in any such direction. 76. The combination of claim 75 further comprising means (166,182,184) for precisely locating the tool carriage relative to the tool head at a predetermined reference position. 77. The combination of claim 75 wherein the carriage (128) is

hollow. 78. The combination of claim 75 or claim 77 wherein the carriage (128) has an exterior surface which in transverse cross section is polygonal. 79. The combination of claim 75 wherein the guide means includes plural sets of rollers. 80. The combination of claim 79 wherein at least one set of rollers includes plural non-yieldably mounted rollers and plural yieldably mounted rollers coacting on respective portions of the carriage (128). 81. The combination of claim 80 wherein the yieldably mounted rollers are pre-loaded by said spring means. 82. In a turning machine having a head on which a tool is selectively positionable toward and away from a workpiece by a prime mover and a carriage an improved prime mover and carriage combination for selectively positioning the tool on the head characterized by low friction, low inertia, and rapid response to input commands and comprising an electric linear motor forming the prime mover wherein one end of the carriage is adapted to be coupled to the cutting tool, the other end of the carriage is coupled to the motor for transmitting linear motion and wherein said linear motor and carriage are mounted on the head of the machine; and a fixed reference scale (220) in the form of a grating mounted on the carriage for movement therewith and a sensing head (222) mounted on the machine head laterally adjacent the line of travel of the scale (220), the motion of the scale (220) past said sensing head (222) causing said sensing head (222) to provide a position signal correlating the position of the scale (220), and hence the carriage on the machine head.