Expert: David Story - 9/12/2009

Question
how dose industrial robots hold their position under loads ?
what are the gears and mechanisms used beside motors
what type of sensors do they have do they use sensors or encoders to read the movement of motors?

Answer
Thanks for the question.

Robots hold their positions entirely by servo motors. The motors have encoders which send the feedback to the controller. Depending on the manufacturer there are many different types of mechanical power transmission for the arms. Some axes, typically axis 1, or the axis that controls circular movement of the robot are direct drive but that is not always the case as well.

There is also a possibility to use program control to allow a specified amount of travel deviation. This is done to allow the robot a slight amount of freedom of movement to allow for greater speeds from one point to another. Typically this deviation is less than 10mm but can be as great as 100mm if the amount of free air space is there. This can cause beginning programmers a great amount of frustration in areas where the motion is limited. Many robots have been crashed in an attempt to gain cycle time by allowing greater range of motion. Precision and speed are constant enemies when dealing with robotics. It is very difficult to attain both.

I hope this answers your questions.

Very best regards,
David E. Story