Method for monitoring the track generated by the control of the drives of computer controlled machine tool or an industrial robot

In a computer-controlled machine tool or industrial robot having first and second drives for movement along a track plottable in a Cartesian coordinate system defined by two axes, first and second controllers for controlling said first and second drives, respectively, in response to first and second corresponding reference values generated by a system program according to a predetermined track velocity, a method of controlling said drives comprising the steps of:

• A. supplying said first and second reference values to a respective first and second system model to obtain corresponding first and second predicted position values indicative of the actual track of the drives;
• B. comparing said first and second predicted position values, respectively, to said first and second reference values;
• C. generating first and second position error signals corresponding to the differences of said firts reference value and first predicted position value, and second reference value and second predicted position value, respectively;
• D. taking the square root of the sum of the squares of said position error signals to form a square root error signal;
• E. comparing said square root error signal to a threshold value;
• F. reducing said first and second reference values by predetermined amounts if said square root error signal exceeds said threshold;
• and
• G. supplying said reference value to said controllers when the corresponding squrae root error signal is below said threshold value.