Disclosed is a method for estimating angular errors of coders for a looped system including a rotating actuator and an angle coder producing a position measurement signal, and including a calculation device controlling the actuator, the calculation device receiving a setpoint signal, as well as the measurement signal, for looping, the calculation device calculating in a corrector a control signal. In a test phase, a specific corrector C.sub.ω.sub.rj(q) is synthesised for constant rotation speed ω.sub.rj, the corrector having substantially zero gain at the frequency and harmonics, resulting in opening the loop at the frequencies, a matrix relation is established between position measurements and a function of parameters characterizing the coder errors and the torque ripples, the test phase repeats with different speeds, the matrix relations are concatenated producing an identifiable global matrix relation, the encoder error and torque ripple parameters are estimated by resolution of the global matrix relation.

An instant correction method for an encoder includes the following steps. The motion of a device under test is sensed to obtain a first wave signal and a second wave signal. The first and second wave signals are sampled to generate N first digital signal values and N second digital signal values. N positioning positions are generated according to the N first and second digital signal values, and the N positioning positions are added to a calculation group. A regression analysis is performed for the calculation group to generate a regression curve. The (N+1)-th prediction position is predicted using the regression curve. The ideal position of the device under test is determined at a time point of the (N+1)-th prediction position according to an ideal position curve. An error value between the (N+1)-th prediction position and the ideal position is applied to correct the device under test.

An instant correction method for an encoder includes the following steps. The motion of a device under test is sensed to obtain a first wave signal and a second wave signal. The first and second wave signals are sampled to generate N first digital signal values and N second digital signal values. N positioning positions are generated according to the N first and second digital signals, and the N positioning positions are added to a calculation group. A regression analysis is performed for the calculation group to generate a regression curve. The (N+1)-th prediction position is predicted using the regression curve. The ideal position of the device under test is determined at a time point of the (N+1)-th prediction position according to an ideal position curve. An error value between the (N+1)-th prediction position and the ideal position is applied to correct the device under test.

The present invention provides a configuration which enables an improvement in the workability of wiring of a sensor in a servo system. An encoder detects the operation of a motor driven by a servo driver, and generates a feedback signal indicating the detected operation. Further, the encoder receives detected signals output from sensors for detecting an object driven by the motor via sensor cables. The encoder outputs the feedback signal and the input detected signals to the outside.