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I am working with a position-controlled manipulator. However, I want to implement a torque-controlled method on this robot. Is there any way to convert a torque command to a position command?

I try to find research papers on this but I have no idea where I should start or which keywords I should use in searching. Do you have any suggestion?

Petch Puttichai
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  • Can you describe the problem in more detail? You might want to look into 'impedance control' technique. – Eugene Sh. Dec 01 '14 at 18:32
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    @EugeneSh. Actually impedance control is what I want to implement on the robot. The problem is that I can calculate a set of input joint-torque commands but the robot is joint-position controlled. So I would like to know if there is any way to translate joint-torque commands to joint-position commands. – Petch Puttichai Dec 02 '14 at 03:15
  • Use PID controller. Your input will be the desired position. PID controller generates a torque that moves the manipulator to the desired position. – CroCo Dec 02 '14 at 18:40
  • @PetchPuttichai But what the arm should actually do? Follow some trajectory? Point to point movement? Movement with maximum exerted external force? If you need a torque/force or impedance control, you will need torque/force feedback from sensor or from observer based on your motors feedback. Are you able to provide it? – Eugene Sh. Dec 03 '14 at 15:08
  • @EugeneSh. The task may be to assemble furniture parts, or something like that. I think I have to implement impedance control in some way but now I still do not have concrete understanding or clear picture about it. Feedback information is available. – Petch Puttichai Dec 06 '14 at 09:11
  • In stack exchange, it is better to edit your question to add information requested in comments, rather than adding more comments. Comments are for helping to improve questions and answers, and are distracting, so we try to keep them to a minimum. If all of the information needed to answer the question is contained within it, the comments can be tidied up (deleted). – Mark Booth Jun 22 '15 at 13:26
  • Dear friends did you find a good solution for Implementing a torque-controlled strategy on a position-controlled robot? – milad Jun 18 '15 at 15:12
  • Hi milad. Welcome to Robotics Stack Exchange. Please do not answer a question with another question like this. If the answers in this thread don't satisfy you, please consider posting your own question as a new thread. – Ben Jun 18 '15 at 23:32
  • Thinking about your question @PetchPuttichai, can you confirm that you have a robot which takes position inputs only, and you have no control over the torques to the motors? If so, then I presume that you are attempting to simulate torque control by stepping to a position just short of or just beyond the actual desired position. This sounds like a difficult problem, fraught with dangers. Is there any reason why you can't switch your motors into toque control mode? Are your motors steppers for instance? – Mark Booth Jun 22 '15 at 13:32

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We find this recent paper by Andrea Del Prete, Nicolas Mansard, Oscar Efrain Ramos Ponce, Olivier Stasse, Francesco Nori quite interesting:

Implementing Torque Control with High-Ratio Gear Boxes and without Joint-Torque Sensors

The authors presented a framework for implementing joint-torque control on position controlled robots.

Petch Puttichai
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  • Thanks for your answer Petch Puttichai, but we prefer answers to be self contained where possible. Links tend to rot so answers which rely on a link can be rendered useless if the linked to content does rot. If you add more context from the link, it is more likely that people will find your answer useful. – Mark Booth Jun 22 '15 at 13:21
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Robotic arm are basically controlled using torque input to reach a position reference. Most common control techniques for such robot are computed torque (also called inverse dynamics approach), and P-D controller with gravity compensation.

You can find all the information you need on the bible of robot modeling and control, Robot Modeling and Control, Spong W. and al., 2005.

PS: searching papers about that subject is a very bad idea since this is no new controller that you are looking for, this is well established control techniques.

Alexandre Willame
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Many robotics textbooks should have descriptions on control algorithms for arm. Typically, you will wrap position or velocity control around torque control. You can use PID control for this, but i think there are other methods.

Ben
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Check out this paper by Oussama Khatib, Peter Thaulad, Taizo Yoshikawa and Jaeheung Park from the Stanford Artificial Intelligence Laboratory:

Glorfindel
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EdibleRobot
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  • Thanks for your answer EdibleRobot, but we prefer answers to be self contained where possible. Links tend to rot so answers which rely on a link can be rendered useless if the linked to content does rot. If you add more context from the link, it is more likely that people will find your answer useful. – Mark Booth Nov 30 '15 at 17:35