Digital robot control having an improved pulse width modulator

A digital control for a robot having a plurality of arm joints, said control comprising:

• an electronic motor for driving each of the robot arm joints;
• a power amplifier for each of said motors having power switching devices operable by sensing the current in an external sense resistor for each motor and power amplifier pair, to supply current to the motor for forward, non-forcing and reverse operation;
• a digital pulse width modulator circuit for operating the power amplifier switching devices for each aarm joint;
• said modulator circuit including up/down counter means for generating a sawtooth waveform, and congruently imposing a time interval centered on an apex of said sawtooth waveform defining a control pulse width for a current sensing measurement, by counting up to and down from predetermined endpoints as a function of time;
• means for comparing the count of the counter means for the sawtooth waveform to a signal representing a control command so as to define a time span needed to operate a power amplifier and energize an associated joint drive motor in accordance with the control command;
• means for generating a first output control pulse for power amplifier switching when one drive polarity is commanded, said first output control pulse having a width corresponding to the defined time span and based on a count comparison referenced to the upper endpoint of the sawtooth waveform;
• and
• means for generating a second output control pulse for power amplifier switching when the other polarity is commanded, said second output control pulse having a width corresponding to the defined time span and based on a count comparison referenced to the lower endpoint of the sawtooth waveform;
• and
• feedback control loop means for each arm joint and including at least digital position, velocity and current control loops looping through and operating the associated pulse width modulator circuit.

A robot having:

• an arm with a plurality of joints;
• each of said joints having an electric drive motor associated therewith;
• a power amplifier for operating each of said motors by sampling the motor current in a sense resistor remotely sensitive to each associated said motor;
• digital pulse width modulator circuit means for operating each power amplifier;
• each pulse width modulator circuit means including up/down counter means for generating a sawtooth waveform by counting to upper and lower endpoints, each endpoint is adapted to be symmetrically straddled by respective upper and lower control pulse intervals for defining a sensing interval for sampling motor current as a function of time;
• means for comparing the counter means count for the sawtooth waveform to a signal representing a control command so as to define a time span needed to operate a power amplifier and energize an associated joint drive motor in accordance with the control command;
• means for generating a first output control pulse for power amplifier switching when one drive polarity is commanded, said first output control pulse having a width corresponding to the defined time span and based on a count comparison referenced to the upper endpoint of the sawtooth waveform;
• and
• control loop means for each arm joint and including at least digital position, velocity and current control loops looping through and operating the associated pulse width modulator circuit.

A system for energizing and controlling a robot arm joint motor comprising:

• at least one winding for said motor;
• a power amplifier for energizing said motor winding;
• said power amplifier having first switching means for energizing said motor winding in the forward direction and second switching means for energizing said motor winding in the reverse direction and a sense resistor responsive to the current in both of said motor winding directions;
• a digital pulse width modulator circuit having up/down counter means for generating a counting period as a function of time;
• means for comparing the counter means counting period to a signal representing a control command so as to define a time width of at least a first output control pulse for operating said first switching means and a time width of at least a second output control pulse for operating said second switching means according to the control command magnitude and a command polarity;
• and
• means for generating respective signals for operating said first and second switching means to force current to be conducted through said motor winding in each direction for a short period of time stationed at the count extremities, in each cycle of said counter.

A digital pulse width modulator circuit for operating power amplifiers and joint motors during positive and negative drive polarity as well as non-forcing request commands, by measuring the motor current during a sensing interval in an associated sense resistor for each joint motor in a robot control comprising:

• up/down counter means for generating a sawtooth waveform, having positive and negative apexes adapted for control pulse positioning for defining the sensing interval in which to measure the current from each joint motor through said associated sense resistor, by counting up to and down from an upper endpoint to a lower endpoint as a function of time;
• means for comparing the count of the counter means for the sawtooth waveform to a signal representing a control command so as to define a time span needed to operate a power amplifier and energize an associated joint drive motor in accordance with the control command request and for sampling the motor current in the sense resistor at a point in time midway between the beginning and end of the control pulse sensing intervals, the current sampling time occurring only at the apexes of said sawtooth waveform having one predefined polarity;
• means for generating a first output control pulse for power amplifier switching when one drive polarity is commanded, said first output control pulse having a width corresponding to the defined time span and based on a count comparison referenced to the upper endpoint of the sawtooth waveform;
• and means for generating a second output control pulse for power amplifier switching when the other polarity is commanded, said second output control pulse having a width corresponding to the defined time span and based on a count comparison referenced to the lower endpoint of the sawtooth waveform, said pulse width modulator circuit thereby measuring the motor current synchronously to control said robot, including at those times when the motor is regenerating while a non-forcing command is requested.