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US 4,902,944 AGranted
Digital robot control having an improved current sensing system for power amplifiers in a digital robot control
AssigneeStaubli International AG.
InventorsKenneth E. Daggett, Eimei M. Onaga, Richard J. Casler, Jr., Richard A. Johnson, Leonard C. Vercellotti
Life of this patent
Estimating the term…
Abstract
A digital control for a multiaxis robot includes position, velocity and torque controls that drive a motor voltage control loop. Pulse width modulated control signals operate power switches in a power bridge to control the current to each robot joint motor. A single resistor is connected in the bridge circuit to supply motor current feedback needed for control loop operation.
Claims13
A system for energizing a robot arm joint motor and for sensing motor current for feedback control, said system comprising:
- a power amplifier including a bridge circuit with a plurality of legs each having one end thereof connected to supply drive current to the motor from a power supply connected across said bridge circuit to the other ends of said legs;
- a semiconductor switch having a control terminal, one said switch connected in each bridge leg with a control signal being applied to the control terminal to make that bridge leg switchably conductive;
- digital control means for cyclically generating switch control signals that are pulse width modulated to operate said power switches and produce motor drive current having direction and magnitude required by cyclically generated robot drive control commands;
- said digital control means generating said switch control signals to make each motor supply current path through said bridge circuit conductive over at least a short portion of each control cycle, according to forced switching patterns, the direction and amplitude of the current through the motor being adapted to be sampled with a single sense resistor, independent of the number of legs in the power bridge;
- means for cyclically sampling the current from the power supply to said bridge circuit via the single sense resistor, at a predetermined time interval during the forced patterns of semiconductor switch conduction in each controlled cycle of the motor supply path and in synchronism with the digital control means cycle and within said short cycle portion, so that the sampled current is forced to flow through the single sense resistor at a time when it accurately indicates the magnitude and polarity of average current flowing in the motor;
- and
- said sampling means further coupling signals representing the current samples to said digital control means to provide feedback control over the generation of said robot drive control commands.
4 more elements
A system for energizing a robot arm joint motor and for sensing motor current for feedback control, said system comprising:
- a power amplifier including a bridge circuit with a plurality of legs each having one end thereof connected to supply drive current to the motor from a power supply connected across said bridge circuit to the other ends of said legs forming a terminal junction;
- a semiconductor switch having a control terminal, one said switch being connected in each bridge leg with a control signal to make that leg conductive when the control signal is applied to said switch control terminal;
- central resistance means serially connected between said bridge circuit and the power supply at the external junction of the plurality of legs in the plural leg bridge circuit;
- digital control means for cyclically generating switch control signals that are pulse width modulated to operate said power switches and produce motor drive current having direction and magnitude required by cyclically generated robot drive control commands;
- said digital control means generating forced patterns of said switch control signals to make each motor supply current path through said bridge circuit conductive over at least a short portion of each control cycle;
- means for cyclically sampling the direction and magnitude of the current through said central resistance means, at a predetermined time interval during the forced patterns of semiconductor switch conduction in each controlled cycle of the motor supply path and in synchronism with the digital control means cycle and within said short cycle portion, the direction and magnitude of the current through the motor being adapted to be accurately indicated by the current through said central resistance;
- and
- said sampling means coupling signals representing the current samples to said digital control means to provide feedback control over the generation of said robot drive control commands.
5 more elements
A robot having:
- an arm with a plurality of joints;
- each of said joints having an electric drive motor associated therewith;
- each of said motors coupled to a power amplifier including a bridge circuit with a plurality of legs each having one end thereof connected to supply drive current to the motor from a power supply connected across said bridge circuit to the other ends of said legs;
- a semiconductor switch having a control terminal, one said switch being connected in each bridge leg to make that leg to be conductive when a control signal is applied to said switch control terminal;
- resistance means adapted for central sampling, serially connected between said bridge circuit and the power supply, independent of the number of legs in the plural leg bridge circuit;
- digital control means for cyclically generating patterns of switch control signals that are pulse width modulated to operate said power switches and produce motor drive current having direction and magnitude required by cyclically generated robot drive control commands;
- means for cyclically sampling the current through said resistance means at a predetermined time interval, during the patterns of semiconductor switch conduction in each controlled cycle of the motor supply path, in synchronism with the digital control means cycle and within said short cycle portion;
- said digital control means generating the patterns of said switch control signals to force each motor supply path through said bridge circuit to be conductive over at least a short portion of each control cycle, the direction of the current through the motor adapted to be sampled, the sampled current through the resistance means flowing therethrough, at a time when it accurately indicates the polarity and average of the current flowing in the motor;
- said sampling means coupling signals representing the current samples to said digital control means to provide feedback control over the generation of said robot drive control commands;
- one of said power amplifiers with its resistance means and current sample coupling means being provided for each joint motor;
- and
- said digital control means generating switch control signals for switches in each of said power amplifiers.
9 more elements
Dependencies are inferred from the claim text.