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Student
Posts: 21 Apprentice
Finding a hole |
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Answered | |
/ Most recent by Karine_Simard |
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Hi! I am working on an application where the cobot has to take a gauge with the gripper and then go to a hole in an engine to measure. I am using to find the hole a camera from Cognex. The problem is that when I send the coordinates to the cobot and moves to the hole to measure, I loose some precision, so sometimes it is impossible to enter into the hole.
Do you know how can I improve the application finding the hole? I know the best solution is to use a force torque sensor (with spiral search or so) but I don't have any actually...
Thanks!
Do you know how can I improve the application finding the hole? I know the best solution is to use a force torque sensor (with spiral search or so) but I don't have any actually...
Thanks!
Best Answer
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matthewd92 Founding Pro, Tactile Sensor Beta Testers Posts: 1,252 Handy
@Student So here are a couple of examples of using a pin to gauge a hole. The first image is of a standard type pin gauge, where there is a nice square corner which you as a human can still easily handle. The second shows the gauge having some lead-in, quite exaggerated in this example.
As you can imagine its much easier to get the second one started in the hole. By using the Force wizard you can place a waypoint inside of a force node and allow the robot to float in the XY directions if you are for example moving in the Z direction to insert the pin.
As far as how to implement the spiral search in polyscope refer to this post. The difference is you will need to place into a background thread a feature to find the forces on the robotThread forceOnArm = get_tcp_force() #This returns a list of forces in X,Y,Z, Rx, Ry, Rz on the TCP Fx = forceOnArm[0] Fy = forceOnArm[1] Fz = forceOnArm[2] sync()
You could the just substitute this into program that @Tyler_Berryman produced. The thread where the idea Tyler did came from is located here
Hope this helps
How repeatable/precise is is the measurement coming from the camera? Understand the robot only has a precision of .004"/0.1mm so if your hole tolerance is less than that the robot will have a hard time anyways.
Another option without seeing your gauge is to provide some lead-in on the edge of the gauge and then allow the robot to float in the XY directions while you move the gauge in the Z direction allowing the gauge to find its own way into the hole. You would use the force wizard and a frame motion type to achieve this.
I don't know exactly what you mean in your third paragraph. And how can I implement the spiral search in Polyscope?
Thanks!
Just one more question. Can I move in X and Y axis while applying a force in the Z axis? I mean, I want to do the spiral search keeping the force in Z axis until the cobot finds the hole, so the Z axis will change.
To answer your other question, yes you can do that. Just use the Forze wizard and make the z-axis compliant using the tool frame, then give it the amount of force to use. Also, one tip, reduce the amount of speed that it uses from the default amount down to something like 25 mm/sec and then work up in speed until it does what you want.
I have implement the script and edited and now I can use it. But I have a big problem, I need to measure different holes of a block (from an engine) but to do the spiral search I need to contact the gauge and the block, so doing the spiral search the gauge scratches the block while finding the hole. Is it other way to do it without contact?
Its really hard hard to know what to tell you without being able to see the actual application.
So I need to find exactly the center of the hole but the spiral search sractches the block... @matthewd92
To get a better precision with your optic system without changing your camera, you can try to reduce the field of view (if it's possible...) but you'll probably have to change/add a lense to your camera.
Another option could be using a force sensor like the FT300. You'll still scratch the block but as you'll get a better precision with this kind of sensor you'll be able to apply less pression.
Thanks to everyone!
Karine Simard
Proud member of the DoF Crew
Director of Marketing
Robotiq
[email protected]
https://streamable.com/bgwtl
Karine Simard
Proud member of the DoF Crew
Director of Marketing
Robotiq
[email protected]