Servo system employing a tracking digital angle encoder

A servo positioning system for moving a shaft to a desired angular position in response to a digital command input signal comprising:

• a resolver connected to the shaft providing an output signal in trigonometric form indicating the position of the shaft;
• analog to digital converter means, connected to said resolver output, providing a digital response signal which is dependent on the output signal of said resolver;
• comparator means connected to receive the digital command input and the digital response signal for providing a digital error signal equal to the difference;
• primary control means connected between said comparator means and the shaft to move the shaft to a position where the error signal of said comparator means approaches zero;
• said analog to digital converter means providing a trigonometric representation of the difference between the trigonometric output of said resolver and the digital response signal;
• and
• analog lock means, activated when the digital error signal is within a predetermined distance from zero, connected between said analog to digital converter means and the shaft to maintain the shaft near the desired position so that the trigonometric representation of the difference between the trigonometric output of said resolver and the digital response signal is maintained below a predetermined small value.

A positioning servo for positioning a shaft in response to a digital command input signal comprising:

• resolver means connected to the shaft giving an analog signal indicating the position of the shaft;
• a digital counter providing a digital output signal determined by an input signal;
• translator means receiving the analog signal from said resolver and the digital signal from said counter and providing an analog difference signal which represents the difference between the analog signal from said resolver and the digital output signal from said digital counter;
• detector feedback means connected between said counter and said translator and utilizing the analog difference signal to keep said counter within one bit of the angular position represented by said analog signal;
• subtractor means connected to receive the digital command input signal and the digital output signal from said counter and providing a digital difference;
• and
• positioning means connected between said subtractor means and the shaft to rotate the shaft to a position where the digital difference is zero.

A servo positioning system for positioning an item in response to an absolute digital input command comprising:

• a servo motor for positioning the item;
• a servo motor controller for controlling operation of said servo motor in response to an analog input signal;
• a resolver for providing an analog indication of the position of an item to be positioned;
• a digital angle encoder connected to said resolver providing both a digital representation of the item position, and an analog difference signal of the difference between the resolver analog indication of the item position and the digital representation of the item position;
• a digital to analog converter connected to said servo motor controller for supplying an analog control signal thereto in response to a digital input;
• digital control means for supplying a digital input signal to said digital to analog converter for moving the item to be positioned to a desired position indicated by a digital command input signal;
• and
• analog lock means connected to said digital angle encoder to be activated when said digital control means moves the item to a position separated from the desired position by a predetermined distance from the digital command input signal position utilizing the analog difference signal for operating the servo motor controller to maintain the item within a predetermined position of the desired position.