Video probe aligning of object to be acted upon

Abstract

An aligning system includes an object to be acted upon at predetermined locations, such as a circuit board to receive solder paste. There is a device, such as a stencil, characterized by the pattern for acting upon the object. A video probe is arranged to look at both the device and the object for providing image signals representative of both. A comparator compares the image signals to provide an error signal representative of misalignment between the device and object. A positioner responsive to the error signal relatively positions the device and object to reduce the error. An operator causes the device to operate upon the object at the predetermined locations.

Description

11loos looks at the stencil. This next prompt instructs the operator to rotate the vision probes throu through 180° to look at the stencil. The operator then rotates mirror tubes 32 through the 180° established by the rotate clamps 42. The operator then drives the screen into position above the board with joy stick and θ push button controls on the ASP-24 machine. The operator positions the overhead structure in x, y and θ into a position such that the vision probes observe the pattern on the screen or stencil that matches the pattern on the circuit board previously aligned centered within the field of view of the probes. In response to each actuation of button 14A the menu prompts the operator to teach the pattern that is desirable after manually locating the stencil. The operator may be required to make fine adjustments in the window by moving trackball 14D and changing the window size until the object is clearly defined and boxed in a square on monitor 15. The operator then depresses push-button 14B and thereby teaches the system the pattern it is looking for with the first probe. The operator follows the same procedure for the second probe. Then the operator pushes button 14C to indicate teaching is complete.

The screen printer then makes a number of automatic moves to learn the geometry associated with this particular setup and this particular type board.

The x stepper motor first moves the screen printer a predetermined number of steps in the x direction. This movement defines the world coordinate system for the cameras 33. Because of this feature the cameras may be placed at any angle anywhere along the front of the circuit board. The y stepper motors then move the screen printer a predetermined number of steps in the orthogonal y direction to confirm the world coordinate system. The system also recognizes the number of steps per pixel during these x-y moves. These moves enable recognition of how much the image moves for every step of the stepper drive system. Then the stepper motors move the screen printer through pure rotation a predetermined number of steps to determine how the object translates in x and y coordinates during a pure rotation. The printer repeats these translational and rotational movements.

The system has thus recognized how the object moves in x and y and how it translates in x and y during a rotational move. This information on these moves allows the system to learn trigonometric solutions of several triangles.

Referring to FIG. 6, there is shown a diagrammatic representation of moves in x, y and θ helpful in understanding the principles of the invention involved in learning the geometry of the circuit boards and stencils. The pattern is characterized by a center of rotation 111. The apparatus may learn from looking at the stencil or screen driven by the stepping motors with reference to two points, such as 112 and 113, that are some vector distance away from the center of rotation 111. First performing a move in the x direction facilitates learning the world coordinate system and steps per pixel confirmed by a movement in the y direction. The following rotational moves involves taking a picture of the objects, such as 112 and 113, after an incremental move in one direction, typically counterclockwise, followed by a move from the initial position in the opposite direction by the same increment from the initial position, typically clockwise. The moves in the x and y direction basically define right triangles having a hypotenuse of magnitude corresponding to the square root of the sum of the squares of the incremental displacements in the x and y directions. The angular displacements effectively create two isosceles triangles from the shifts about points 112 and 113 with the center of rotation 111 being the common vertex for both isosceles triangles. The invention facilitates learning the geometry of the board by looking at only two points and making moves in x, y and θ directions for each of these points.

An operator may select any target point that appears unique on the board such that it may be distinguished from other target points around it, choose a second target point similarly distinguishable from other surrounding targets, and teach the apparatus the geometry of the board such that when any circuit board enters the apparatus out of line with the stencil, the video probes looking at the board automatically download the proper x, y and θ moves for the stencil to bring stencil and board into alignment.

The operator then rotates both probes to look down at the board. Looking now at the board, the system learns the pattern on the board which correlates with a pattern on the screen. The operator has then completed the automatic setup.

It may be desirable to modify this procedure slightly. For example, it may be desirable to rotate the probes to look up again after the system has learned the circuit board pattern to better correlate circuit board and screen or stencil images.

With the probes then looking at the board, the operator may then select auto print on the main menu, and the apparatus is then ready for a production run. During a production run, both probe assemblies index into position after the board has been brought in, recognize the patterns that is learned on each of the probes and automatically moves the screen relative to the board to align the stencil very accurately with the board. The probes then moves into the retracted position, printing occurs and the board just properly printed exits the machine. A new board enters, set down against the vacuum stop, the probes move to the extended position, the apparatus recognizes the patterns, downloads to the stepper motors the proper movements to align the stencil with the circuit board, print, exits, and the process repeats.

As an alternative, the operator may edit a setup. If an operator notices that the screen printer is printing consistently off the pad in one direction or other, the operator may select edit setup from the menu and modify where the screen printer is printing by selecting a predetermined direction and distance of correction. Thereafter, the apparatus will automatically print consistently in the new location and continue to print in that location until modified again.

A feature of the invention is the lighting arrangement for back lighting the stencil. Stencils and screens are usually shiny or have objects on the bottom which may be confused with object features to be taught. By laying the translucent material on the stencil and providing a light behind it, back lighting occurs which prevents this problem. This arrangement disperses the light in a manner that clearly defines each hole in the stencil relative to any type of reflective background that might occur.

The invention has a number of features. The vision probes enter between circuit board and stencil and perform the alignment as distinguished from looking at the board outside the screen printer.

There has been described novel apparatus and techniques for aligning. It is evident that those skilled in the art may now make numerous other uses and modifications of and departures from the apparatus and techniques herein disclosed without departing from the inventive concepts. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in or possessed by the apparatus and techniques herein disclosed and limited solely by the spirit and scope of the appended claims. ##SPC1##

Claims

1. Aligning apparatus comprising,

an object to be acted upon at predetermined locations defining a pattern,

a device characterized by said pattern for acting upon said object,

a video probe arranged to look at both said device and said object for providing image signals representative of both,

means for comparing both image signals to obtain an error signal representative of misalignment between the device and object,

means responsive to said error signal for relatively positioning translating and rotating said device and said object to reduce said error,

and means for operating upon said object with said device upon said predetermined locations.

2. Aligning apparatus is accordance with claim 1 wherein said video probe comprises a mirror tube having a mirror at one end intersecting the mirror tube axis at an angle of substantially 45° and exposed through an opening in the wall of said mirror tube,

a video camera located at the other end of said mirror tube for receiving images reflected from said mirror,

said mirror tube being rotatable about the mirror axis between at least a first position exposing said mirror to said device and a second position exposing said mirror to said object.

3. Aligning apparatus in accordance with claim 1 and further comprising,

an object to be acted upon at predetermined locations defining a pattern,

a device characterized by said pattern for acting upon said object,

a video probe arranged to look at said device and said object for providing image signals representative of both,

means for comparing both image signals to obtain an error signal representative of misalignment between the device and object,

means responsive to said error signal for relatively positioning said device and said object to reduce said error,

and means for operating upon said object with said device upon said predetermined locations,

a second of said video probes spaced from the first-mentioned video probe arranged to look at both said device and said object for providing image signals representative of both at areas thereof different from the areas viewed by said first-mentioned video probe,

and means for relatively displacing said video probes while in fixed relative relation and one of said object and device predetermined incremental distances in first and second orthogonal directions and a rotational directional to provide a reference image signal characterizing said pattern.

4. Aligning apparatus is accordance with claim 3 and further comprising:

for each of said video probes video probe support means for selectively moving the associated video probe between a first position located between said device and said object and a second position outside the region between said object and said device,

and means for locating the associated video probe in said first position before acting upon said object and then displacing said video probe to said second position after relatively positioning said device and said object to reduce said error and operating upon said object with said device upon said predetermined locations with the associated video probe in said second position.

5. Aligning apparatus in accordance with claim 4 wherein each of said video probe support means comprises,

a movable probe support carrying said video probe,

a fixed base having vertical walls each formed with front and rear slots with each slot having a horizontal leading portion and a depending angled trailing portion,

said movable probe support having elements for riding in said slots to allow said video probe to move between said first position with said video probe extended and said second position with said video probe retracted.

6. Aligning apparatus in accordance with claim 8 5 wherein said movable probe support comprises a main clamp supporting said video probe substantially at its center of gravity and further comprising,

ball-and-cone pieces and reference balls,

said fixed base comprising a vertical bracket carrying one of said reference balls and said ball-and-cone pieces,

said main clamp carrying the other of said reference balls and ball-and-cone pieces arranged so that engagement of said ball-and-cone pieces with mating reference balls defines a reference position of said video probe.

7. Aligning apparatus in accordance with claim 1 and further comprising,

video probe support means for selectively moving said video probe between a first position located between said device and said object and a second position outside the region between said object and said device,

and means for locating said video probe in said first position before acting upon said object and then displacing said video probe to said second position after relatively positioning said device and said object to reduce said error and operating upon said object with said device upon said predetermined locations with said video probe in said second position.

8. Aligning apparatus in accordance with claim 7 wherein said video probe comprises a mirror tube having a mirror at one end intersecting the mirror tube axis at an angle of substantially 45° and exposed through an opening in the wall of said mirror tube,

a video camera located at the other end of said mirror tube for receiving images reflected from said mirror,

said mirror tube being rotatable about the mirror axis between at least a first position exposing said mirror to said device and a second position exposing said mirror to said object.

9. Aligning apparatus in accordance with claim 7 wherein each of said video probes comprises a mirror tube having a mirror at one end intersecting the mirror tube axis at an angle of substantially 45° and exposed through an opening in the wall of said mirror tube,

a video camera located at the other end of said mirror tube for receiving images reflected from said mirror,

said mirror tube being rotatable about the mirror axis between at least a first position exposing said mirror to said device and a second position exposing said mirror to said object.

10. Aligning apparatus in accordance with claim 7 wherein said video probe support means comprises,

a movable probe support carrying said video probe,

a fixed base having vertical walls each formed with front and rear slots with each slot having a horizontal leading portion and a depending angled trailing portion,

said movable probe support having elements for riding in said slots to allow said video probe to move between said first position with said video probe extended and said second position with said video probe retracted.

11. Aligning apparatus in accordance with claim 2 wherein said video probe comprises a mirror tube having a mirror at one end intersecting the mirror tube axis at an angle of substantially 45° and exposed through an opening in the wall of said mirror tube,

a video camera located at the other end of said mirror tube for receiving images reflected from said mirror,

said mirror tube being rotatable about the mirror axis between at least a first position exposing said mirror to said device and a second position exposing said mirror to said object.

12. A method of aligning an object to be acted upon at predetermined locations defining a pattern with a device characterized by said pattern for acting upon said object which method includes the steps of,

positioning a video probe to look at first one of said device and said object and then the other for providing image signals representative of both,

comparing both said image signals to provide an error signal representative of misalignment between said device and object,

relatively positioning translating and rotating said device and said object while sensing said error signal to reduce said error,

and operating upon said object with said device upon said predetermined locations with said object and said device then being in alignment.

13. A method in accordance with claim 12 and further including the steps of moving said video probe between an inside position located between said device and said object,

then locating said video probe in an outside position outside the region between said object and said device,

and operating upon said object with said device only with said video probe in said outside position.

14. A method in accordance with claim 13 and further including the steps of of aligning an object to be acted upon at predetermined locations defining a pattern with a device characterized by said pattern for acting upon said object which method includes the steps of,

positioning a video probe to look at first one of said device and said object and then the other for providing image signals representative of both,

comparing both said image signals to provide an error signal representative of misalignment between said device and object,

relatively positioning said device and said object while sensing said error signal to reduce said error,

operating upon said object with said device upon said predetermined locations with said object and said device then being in alignment,

looking first at one of said device and said object and then the other with a second video probe spaced from the first-mentioned video probe to provide a second set of image signals representative of said device and said object different from the image signals provided by said first-mentioned video and the areas representative thereof,

and relatively displacing said video probes while in fixed relative relation with respect to one of said object and device predetermined incremental distances in first and second orthogonal directions and a rotational direction to provide a reference image signal characterizing said pattern.