Positional control method and system utilizing same

In a PD type of controller for controlling the position of a joint of a robot through its respective motor by providing a first control signal related to a position error signal, a method for increasing the positional accuracy of the controller comprising the steps of:

• generating a function of the velocity signal related to the velocity of the load;
• integrating the position error signal multiplied by the function of the velocity signal to obtain a second control signal;
• and
• combining the first and second control signals to obtain an equivalent resultant control signal wherein when the value of the load velocity is sufficiently high to overcome the effects of sticktion on the motion of the load, the contribution of the second control signal to the resultant control signal is negligible and wherein the second control signal only makes a significant contribution to the resultant control signal when the value of the load velocity is at such a low level that sticktion impinges on the motion of the load.

A positional control system to control a motor for driving a load in response to a position command signal which defines a desired load position, the system comprising:

• first generating means for generating a position feedback signal related to the position of the load;
• second generating means for generating a velocity signal related to the velocity of the load;
• first combining means for combining the position command signal and the position feedback signal to obtain a position error signal;
• calculating means for calculating a first control signal related to the position error signal;
• integrating means for integrating the position error signal multiplied by a function of the velocity signal to obtain a second control signal;
• and
• second combining means for combining the first and second control signals to obtain an equivalent resultant control signal wherein, when the value of the load velocity is sufficiently high to overcome the effects of sticktion on the motion of the load, the contribution of the second control signal to the resultant control signal is negligible and wherein the second control signal only makes a significant contribution to the resultant control signal when the value of the load velocity is at such a level that sticktion impinges on the motion of the load.

In a control system including a PD type of controller for controlling a motor for driving a joint of a robot by providing a first control signal related to a position error signal, the improvement comprising:

• first generating means for generating a velocity signal related to the velocity of the load;
• integrating means for integrating the position error signal multiplied by the function of the velocity signal to obtain a second control signal;
• and
• combining means for combining the first and second control signals to obtain an equivalent resultant control signal, wherein when the value of the load velocity is sufficiently high to overcome the effects of sticktion on the motion of the load, the contribution of the second control signal is negligible and wherein the second control signal only makes a significant contribution to the resultant control signal when the value of the load velocity is at such a low level that sticktion impinges on the motion of the load.