Torque Current Relationship


In the process of developing a new controller for the UR5 robot arm, we need to know with good accuracy the equations that describe its behaviour. One of the main parameters that is necessary for the control of the robot, is the coefficient of the current-torque relationship. Usually, for an electric motor, the torque that it produces is directly proportional to the current that is running through its windings, following an equation:


The purpose of this study was to try to identify what is the value of the parameter α, so that we can use it when designing out controller.

We are currently still working on it, but we thought of showing you a simple experiment to determine this parameter: We add a known weight at a known distance from a joint of the robot, we can therefore know what is the torque applying at the joint. By measuring the current, and by varying the amount of weight/torque that is being applying, we can find which value for α creates a better correspondance with the measured data.

The UR5 carrying a shopping bag with weights in it

The UR5 carrying a shopping bag with weights in it

Of course, this is a very simple methodology that is not considering neither static nor dynamic friction, but we are working on this as well. You will read some news here soon about it.

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