Pick and place machine with improved workpiece inspection

• US 20050123187A1
• Filed: 11/01/2004
• Published: 06/09/2005
• Est. Priority Date: 11/07/2003
• Status: Active Grant

• Current Assignee: CyberOptics Corporation (Nordson Corporation)
• Original Assignee: CyberOptics Corporation (Nordson Corporation)
• Inventors: Case, Steven K., Haugen, Paul R., Bushman, Thomas W., Madsen, David D., Madsen, M. Hope, Gaida, John D.
• Granted Patent: US 7,706,595 B2
• Time in Patent Office: Days
• US Class Current: 382/141
• CPC Class Codes: H05K 13/0812 the monitoring devices being integrated in the mounting machine, e.g. for monitoring components, leads, component placement

Abstract

Embodiments of the present invention improve upon component level inspection performed by pick and place machines. Such improvements include measuring the travel of a pick and place machine placement nozzle and the motion characteristics of the workpiece through the placement process. Since the component is placed on the workpiece with some force to ensure proper adhesion to the workpiece, some deflection of the workpiece is expected during the placement cycle. The placement force is adjusted to ensure that the component is safely placed into the solder paste or adhesive. Placement force is adjusted through a number of characteristics including: choice of spring tension in the nozzle; the length of the nozzle and the amount of over-travel into the board; the rigidity of the board and design; and the placement of the board support mechanisms. With proper adjustment of these characteristics and parameters, high quality placements onto the workpiece can be ensured. To properly adjust these parameters, a method of measuring the workpiece motion and nozzle travel is provided.

Claims

1. A pick and place machine for placing a component upon a workpiece, the machine comprising:

a placement head having at least one nozzle for releasably holding the component;

a robotic system for generating relative movement between the placement head and the workpiece;

an image acquisition device disposed to obtain a plurality of images of a placement location of the component;

an image processing device for analyzing the images generated by the image acquisition device;

wherein image process analysis measures at least one characteristic of the workpiece movement during a placement cycle.

2. The pick and place machine of claim 1, wherein workpiece movement is vertical movement.

3. The pick and place machine of claim 2, wherein the image processing device measures vertical movement by applying image correlation to the plurality of images.

4. The pick and place machine of claim 3, wherein a position of a correlation peak is indicative of the workpiece movement.

5. The pick and place machine of claim 1, wherein the pick and place machine is a Cartesian pick and place machine.

6. The pick and place machine of claim 1, wherein the pick and place machine is a turret pick and place machine.

7. The pick and place machine of claim 1, wherein at least one of the plurality of images is a blurred image acquired using an exposure time that is longer than a period of a natural frequency of the workpiece.

8. The pick and place machine of claim 7, wherein the measured movement is a function of a blur length in the blurred image.

9. An image acquisition system for use in a pick and place machine, the device comprising:

an image acquisition device for acquiring an image of the workpiece at an intended placement location;

an image processing device operably coupled to the image acquisition device to process the image of the placement location; and

wherein the image processing device determines at least one characteristic of the movement of the workpiece during a placement cycle.

10. The image acquisition system of claim 9, wherein workpiece movement is vertical movement.

11. The image acquisition system of claim 10, wherein the image processing device measures vertical movement by applying image correlation to the plurality of images.

12. The image acquisition system of claim 11, wherein a position of a correlation peak is indicative of the workpiece movement.

13. The image acquisition system of claim 9, wherein at least one of the plurality of images is a blurred image acquired using an exposure time that is longer than a period of a natural frequency of the workpiece.

14. The image acquisition system of claim 13, wherein the measured movement is a function of a blur length in the blurred image.

15. An image acquisition system for use in a pick and place machine, the system comprising:

an imaging device for acquiring an image of the workpiece at an intended placement location;

an image processing device disposed to process the image of the placement location; and

wherein the image processing device determines at least one characteristic of a placement nozzle during a placement cycle.

16. The image acquisition system of claim 15, wherein the at least one characteristic is a position of the placement nozzle at its maximum downward stroke.

17. A method of detecting motion of a workpiece during a pick and place operation the method comprising:

sensing a position of the workpiece before the placement of a component;

sensing the position of the workpiece at least once after the placement of the component; and

comparing the position of the workpiece before and after placement to determine the movement of the workpiece due to the placement operation.

18. The method of claim 17, and further comprising:

sensing motion blur of at least one image of the workpiece; and

detecting the amount of motion from the amount of the sensed blur.

19. A method of detecting a position of a placement nozzle during a pick and place operation, the method comprising:

sensing a position of the workpiece before placement of a component;

sensing the position of the workpiece at least once after the placement of the component; and

comparing a position of the nozzle tip at a maximum stroke to determine a correct position of the nozzle.

20. A method of detecting a position of a placement nozzle during a pick and place operation, the method comprising:

sensing a position of a workpiece before placement of a component;

sensing the position of the workpiece at least once after the placement of the component; and

comparing a position of the placement nozzle tip at a maximum stroke to determine force applied to the component by the nozzle tip.