Apparatus for milling cams and the like, as for swiss-type screw machine cams

Abstract

The invention is directed to a novel apparatus for milling Swiss-type screw machine cams. The invention provides a highly simplified and economical numerically controlled system enabling Swiss-type screw machine cams and similar articles to be milled with an ease and precision heretofore unattainable otherwise than with highly sophisticated and costly equipment.

In its most typical application, the invention is utilized in the retro-fitting of an existing cutting machine, such as a shaping or milling machine apparatus of otherwise conventional construction. Alternatively, the invention can be applied in the first instance in connection with the manufacture of modified milling machines incorporating the new control system.

The system of the invention utilizes a conventional three axis cutting machine, such as a shaping or milling machine, which is fitted out with a rotary table. Numerically controlled stepping motors are provided for the "X" and "Y" axes of the milling machine, as well as for the rotary table. An otherwise conventional linear interpolator system, which is substantially self contained and commercially available, is connected between one of the linear axis stepping motors and the rotary table stepping motor. By appropriate control of the linear and rotary stepping motors through the linear interpolator, precise, continuous path cutting of involute cam curves is made possible. Such curves are widely utilized in cams for controlling the operation of Swiss-type screw machines, for effecting cutting tool movement at a constant linear speed.

For some Swiss-type screw machines, where the desired cam contour departs slightly from the true involute to accommodate the geometry of the tool supporting arms, the system of the invention provides for programming of the linear and rotary axes to move in the nominal involute relationship, and the "Z" axis of the machine is actuated by a simple mechanical device to introduce the necessary minor geometrical corrections.

The system of the invention provides a highly simplified and economical system for performing a complex milling cutting operation in the production of precision control cams for Swiss-type screw machines.

Description

BACKGROUND AND PRIOR ART

In the operation of Swiss-type screw machines, it is conventional practice to convert the necessary cutting and shaping operations to a contoured program cam which, as it rotates, controls the movement of one or more tools of the machine. In general, a radial inward cutting movement of a tool would be desirably programmed to proceed at a constant linear speed. To this end, the control cam for many conventional machines would have a surface contour in the form of an involute curve. In certain other conventional makes of Swiss-type screw machines, the orientation of the control cams, and the rocker arms which support the cutting tools, is such that the rocking of the arm will effect a slight repositioning of the cam follower in a circumferential direction, as well as in the desired radial direction. For such machines, the nominal involute curve normally desired is modified or "corrected" slightly to take into account the slight circumferential motion of the cam follower.

Heretofore, the laying out and machining of control cams for Swiss-type screw machines has been a slow and painstaking process, requiring highly skilled machinists. In addition, practical difficulties involved in the machining operation have limited the accuracy to which such cams could be milled.

Description of the Drawing

FIG. 1 is a simplified perspective representation of a milling machine incorporating the features of the invention, adapted especially for the milling of control cams for Swiss-type screw machines.

FIG. 2 is a simplified schematic representation of a control system according to the invention, as utilized in the apparatus of FIG. 1.

FIG. 3 is a simplified perspective representation of a modified form of milling machine according to the invention.

FIG. 4 is a block diagram reflecting a system, utilizing the principles of the invention, for operating a plurality of Swiss-type screw machines on a semi-numerically controlled basis, through the use of a single N/C programmed cam milling cutting machine, rather than in its linear-to-linear functions, for the first time enables a Swiss-type screw machine cam to be produced on an economically feasible basis with N/C programmed equipment. The use of the linear interpolation system in this unique manner enables a true involute curve to be cut in the cam blank utilizing only the beginning and ending coordinates of a slope. It is thus possible to achieve an extremely high level of cam cutting accuracy with a highly simplified form of apparatus. In this respect, while the theoretical possibility of N/C controlled cam cutting for Swiss-type screw machines has long been apparent, the practical difficulties of accomplishing the task with conventional N/C equipment were so formidable that N/C cam cutting has never been realized as a practical reality. However, by utilizing the basic principles of the present invention, the operation is suddenly reduced to requiring only simple machinery and simple controls to achieve a complex end result.

An advantageous subsidiary feature of the invention resides in the ability to utilize a correcting cam profile on one of the idle linear axes of the milling equipment. Thus, in the apparatus of FIG. 1, the cam 37 controls the otherwise idle "Z" axis for corrective cutter movement during the cam profiling operations. In the apparatus of FIG. 3, corresponding corrective cam means (not shown) would act between the machine bed 111 and "Y" axis slide 121 to produce a "Y" axis correction as a function of linear movements of the slide 124 in the direction of the "X" axis.

The apparatus of the invention also advantageously may be utilized for both rough cutting and precision cutting, by the provision of a selector switch 41 in conjunction with the "X₁ " and "X₂ " axis, or the "X" and "Y" axis stepping motors as shown in FIG. 1 and FIG. 3 and by switching from the lower to the higher ratio stepping motor in FIG. 1. In this respect, it will be understood that, in a typical N/C controlled system, the stepping motors have preset maximum stepping rates and thus there is no practical arrangement for driving the motors 26, 126 at a rate high enough to perform rough cutting on an economical basis. In the system of the present invention, an otherwise conventional milling machine such as a shaping or milling machine, for example, is either retro-fitted or modified in the manufacture so that only one ("X₁ " or "X" ) of the linear axes includes a high gear reduction between the stepping motor and the associated linear slide. At least one of the other linear axes ("X₂ " or "Y" ) may include the standard gear and thread ratios, and this axis then is available for high speed, low precision linear control.

It should be understood, of course, that the specific forms of the invention herein illustrated and described are intended to be representative only, as certain changes may be made therein without departing from the clear teachings of the disclosure. Accordingly, references should be made to the following appended claims in determining the full scope of the invention.

Claims

1. An n/C controlled system for cutting involute and/or corrected involute cam profiles for Swiss-type screw machine control cams, which comprises,

a. a milling machine having a cutting head and a work supporting slide,

b. said slide having at least one linear axis of movement,

c. a work-holding rotary table mounted on said slide,

d. said cutting head mounting a milling cutter engageable with a cam blank on said rotary table,

e. n/C controlled motors driving said rotary table through rotary movements and said slide through linear movements, and

f. an n/C program control, including a linear-to-linear continuous path interpolator, connected to said table driving motor and said slide driving motor to effect integrated linear and rotary movements of a cam blank relative to said cutter.

2. An n/C controlled system according to claim 1, further characterized by

a. means interconnecting said motors and the respective slide and rotary table for translating incremental rotary movement of said motors into incremental linear movement of said slide and incremental rotary movement of said table,

b. the incremental movement of the slide being not more than 0.0001 inch per rotary increment of the motor, and

c. the incremental movement of the rotary table being not more than 0.01 degree per rotary increment of its motor.

3. An n/C controlled system according to claim 2, further characterized by

a. said milling machine having a second slide mounted along a linear axis disposed at right angles to the first linear axis,

b. an n/C controlled motor for said second slide,

c. means interconnecting said second slide and its motor providing for a linear increment of second slide movement on the order of 0.001 inch per rotary increment of its motor, and

d. selector switch means for connecting the motors for the first or second slides alternatively in association with said rotary table through said interpolator.

4. An n/C controlled system for cutting involute and/or corrected involute cam profiles for Swiss-type screw machine control cams, which comprises,

a. a milling machine having a cutting head and a work supporting slide,

b. said slide having at least one linear axis of movement,

c. a work-holding rotary table mounted on said slide,

d. said cutting head mounting a milling cutter engageable with a cam blank on said rotary table,

e. n/C controlled motors driving said rotary table through rotary movements and said slide through linear movements.

f. an n/C program control, including a linear-to-linear continuous path interpolator, connected to said table driving motor and said slide driving motor to effect integrated linear and rotary movements of a cam blank relative to said cutter,

g. a second slide having a second linear axis of movement at right angles to said first linear axis, and

h. correcting cam means being provided, operative to effect tangentially directed movement of the cutter relative to the circumferential edge of the cam blank, independent of the rotary movement of the rotary table and in accordance with linear movements of said work supporting slide.

5. An n/C controlled system for cutting involute and/or corrected involute cam profiles for Swiss-type screw machine control cams, which comprises,

a. a milling machine having a cutting head and a work supporting slide,

b. said slide having at least one linear axis of movement

c. a work-holding rotary table mounted on said slide,

d. said cutting head mounting a milling cutter engageable with a cam blank on said rotary table,

e. n/C controlled motors driving said rotary table through rotary movements and said slide through linear movements,

f. an n/C program control, including a linear-to-linear continuous path interpolator, connected to said table driving motor and said slide driving motor to effect integrated linear and rotary movements of a cam blank relative to said cutter,

g. means interconnecting said motors and the respective slide and rotary table for translating incremental rotary movement of said motors into incremental linear movement of said slide and incremental rotary movement of said table,

h. the incremental movement of the slide being not more than 0.0001 inch per rotary increment of the stepping motor,

i. the incremental movement of the rotary table being not more than 0.01° per rotary increment of its stepping motor,

j. a second n/C controlled stepping motor providing for a linear increment of slide movement on the order of 0.001 inch per rotary increment of the stepping motor, and

k. control means for selectively rendering effective one or the other of the linear movement-producing stepping motors.