Multi-axis motion generator utilizing feedforward control

• US 4,093,904 A
• Filed: 02/04/1976
• Issued: 06/06/1978
• Est. Priority Date: 02/04/1976
• Status: Expired due to Term

• Current Assignee: Contraves Goerz Corporation
• Original Assignee: Contraves Goerz Corporation
• Inventors: McNally, Paul F., Burig, Robert G.
• Primary Examiner(s): Schaefer, Robert K.
• Assistant Examiner(s): Feldhaus, John J.
• Application Number:
  US05/655,072
• Time in Patent Office: 853 Days
• Field of Search: 318/561, 318/632, 318/616, 318/618, 318/85, 318/675, 235/150.1, 364/116
• US Class Current: 318/616
• CPC Class Codes: G05B 19/353 with speed feedback only
• CPC Class Codes: G05B 2219/41434 Feedforward FFW
• CPC Class Codes: G05B 2219/41437 Feedforward of speed
• CPC Class Codes: G05B 2219/42186 Master slave, motion proportional to axis

Abstract

Apparatus for generating synchronized multi-axis intermittent motion utilizing electronic encoding, memory and a position control system having feed-forward control. A plurality of slave shafts are rapidly and accurately positioned in response to the positioning of a rotatable master shaft, without mechanical interconnections therebetween. An analog transducer is attached to the master shaft providing an analog position output which is fed to a master encoder which feeds a digital output to a plurality of independent digital memory devices. Each digital memory device provides, in response, an output digital signal indicative of the desired position of an associated slave shaft. The output of each memory device, through an appropriate digital-to-analog converter, is fed to a position controller which positions the associated slave shaft as desired. The servo controller includes a feedforward input to speed positioning and reduce system lag. The feedforward velocity signal is obtained by calculating the difference between the present position of the associated slave shaft and the desired future position of the slave shaft to obtain the desired change in the slave shaft position. This difference is multiplied by the absolute value of the master axis velocity to obtain the necessary velocity feedforward signal. The velocity feedforward signal, which is a function of the change in slave shaft position and the velocity of the master shaft represents the velocity at which the slave shaft must be rotated to achieve the desired position while the master shaft moves through one digital increment.

Claims

1. An electrical positioner for positioning a slave shaft in response to the position of a continuously rotating master shaft comprising:

a master shaft encoder providing a digital master shaft position indication;

position determining means connected to said master shaft encoder and providing a digital slave shaft position in response to the digital master shaft position;

a first digital storage connected to and storing the digital output of the associated position determining means;

a second digital storage device;

a shifting means for shifting the digital signal stored in said first storage device to said second storage device when said master axis position changes by one digital increment;

a pair of digital-to-analog converters connected to said first storage device and said second storage device for converting the digital outputs to analog outputs;

multiplying means for multiplying the outputs of said digital-to-analog converters by the signal related to the velocity of the master axis;

subtractor means for subtracting the analog signals out of said digital-to-analog converters providing a velocity feedforward signal;

the velocity feedforward signal is calculated for each incremental change in the digital master shaft position; and

,

positioning means connected for positioning the slave shaft to the digital slave shaft position from said position determining means as function of the velocity feedforward signal.

2. An electrical positioner as claimed in claim 1 comprising:

roll over compensating means connected to said pair of digital-to-analog converters for providing an appropriate correction signal when the indication in said first digital storage means or said second digital storage means goes through the zero transition.

3. Apparatus for positioning a slave shaft in response to the position of a master shaft comprising:

a sequentially changing absolute non-ambiguous master shaft encoder providing a digital master shaft position indication;

a memory device having an input address, connected to receive the digital master shaft position indication, and an output, providing a stored digital position indication in response to the input, which represents a desired slave shaft position;

positioning means connected between said memory device and the slave shaft for positioning the slave shaft comprising;

servo control means utilizing position feedback from the slave shaft to position the slave shaft at the position indicated by the output of the memory device, and

feedforward velocity control means utilizing the change in slave shaft position indicated by the output of said memory device and the velocity of the master shaft to determine velocity to move the slave shaft toward the position indicated by the output of the memory device.

4. Apparatus for positioning a slave shaft in response to the position of a master shaft comprising:

a master shaft encoder providing a digital master shaft position indication;

a memory device having an input address, connected to receive the digital master shaft position indication, and an output, providing a stored digital position indication in response to the input, which represents a desired slave shaft position;

positioning means connected between said memory device and the slave shaft utilizing position feedback from the slave shaft to position the slave shaft at the position indicated by the output of the memory device;

a first storage means for storing the present output of said memory device;

a second storage means for storing the preceding output of said memory device;

master axis velocity means for multiplying the output of said first storage device and said second storage device by the velocity of the master axis;

digital to analog converter means for converting the output of said first storage device and said second storage device from a digital representation to an analog representation;

subtractor means for subtracting the outputs of said first storage device and said second storage device to provide a velocity feedforward signal; and

,

feedforward velocity control means utilizing the velocity feedforward signal to control the velocity at which the slave shaft is moved toward the position indicated by the output of the memory device.

5. Apparatus as claimed in claim 4 comprising:

roll over compensating means for providing correcting compensation when said first storage device or said second storage device goes through a zero transition.

6. An electrically controlled positioning system for synchronously positioning a plurality of slave shafts in response to the position of a rotatable master shaft comprising:

master transducer means connected to said master shaft for supplying an electrical output signal representative of the master shaft position;

an electronic memory device associated with each slave shaft having an input, connected to receive the output signal from said master transducer means, and each electronic memory device is independently programmed to provide simultaneously an individual output signal representative of the desired position of the associated slave shaft with respect to the master shaft position;

servo control means associated with each slave shaft connected between the slave shaft and said electronic memory device for positioning the slave shaft to the position indicated by said electronic memory device so that the plurality of slave shafts are simultaneously positioned in response to the master shaft position; and

feedforward signal means connected to operate each servo controller means to position the associated slave shaft as a function of the desired change in slave shaft position and the velocity of the rotatable master shaft.

7. An electrically controlled positioning system for synchronously positioning a plurality of slave shafts in response to the position of a rotatable master shaft comprising:

master transducer means connected to said master shaft for supplying an electrical output signal representative of the master shaft position;

an electronic memory device associated with each slave shaft having an input, connected to receive the output signal from said master transducer means, and an output, supplying a signal representative of the desired position of the associated slave shaft with respect to the master shaft position;

servo control means associated with each slave shaft connected between the slave shaft and said electronic memory device for positioning the slave shaft to the position indicated by said electronic memory;

storage means for storing the present desired slave shaft position signal and the preceding slave shaft position signal;

subtractor means for subtracting the present desired slave position signal from the preceding slave shaft position signal;

multiplier means for multiplying the difference signal between the preceding desired slave shaft position signal and the present desired slave shaft position signal by a signal representative of the velocity of the master shaft to provide a velocity feedforward signal; and

,

said servo control means associated with each slave shaft utilizing the velocity feedforward signal to position the associated slave shaft as a function of the desired change in slave shaft position and the velocity of the rotatable master shaft.

8. An electrical controller as claimed in claim 7 comprising:

roll over compensation means to provide for the correct calculation of the velocity feedforward signal during zero transition cross over.

9. Apparatus for positioning a plurality of output shafts in response to the position of a master shaft comprising:

a resolver connected to the master shaft providing an analog electrical output indicative of the position of the master shaft;

an encoder having an input connected to the output of said resolver and an output providing a signal in digital form corresponding to its analog input;

a plurality of memory devices each of which can be independently programmed, and each having an input connected to the output of said encoder and having an output which provides a digital signal, determined by the digital input, representative of the desired output shaft position;

a translator associated with each memory device having an analog input, and an analog output providing the algebraic difference between the signals on said digital input and said analog input;

amplifier means connected to the output of said translator;

a servo motor connected to be driven by the output of said amplifier to position one of the plurality of output shafts;

a slave resolver connected to the associated output shaft supplying an analog signal representative of the position of the associated output shaft to the analog input of said translator; and

,

a feedforward network having a tachometer connected to the master shaft and digital storage connected to an associated memory device providing an output signal to the servo motor which is a function of the master shaft speed and the desired change in slave shaft position as determined by the difference between the present digital output signal from the memory device and the preceding digital output signal from the memory device.

10. A positioning system for positioning a plurality of slave shafts in response to the position of a rotatable master shaft comprising:

an analog transducer for sensing the master shaft position and providing an analog output signal representative of the master shaft position;

an analog-to-digital converter connected to said analog transducer providing a digital output signal representative of the master shaft position;

a plurality of independently programmable digital memory devices connected to said analog-to-digital converter each associated with one of the slave shafts and providing a digital output signal representative of the desired slave shaft position with respect to the master shaft position;

digital-to-analog converter means associated with each of said plurality of digital memory device providing an analog signal representative of the desired slave shaft position with respect to the master shaft position;

servo drive means associated with each digital-to-analog converter for driving the associated slave shaft to the desired position in response to the analog signal from said digital-to-analog converter means; and

,

feedforward drive means associated with each digital-to-analog converter for driving the associated slave shaft to the desired position as a function of the difference between sequential output signals of the associated digital memory device and the velocity of the rotatable master shaft.

11. Position control apparatus for positioning a plurality of slave members comprising:

master digital signal means for providing a sequentially changing digital signal;

position determining means associated with each sleeve shaft, each including an independently programmed memory for providing simultaneously a desired position for each slave member from the memory which is addressed by the digital signal from said master digital signal means; and

,

positioning means associated with each programmed memory device for positioning the associated slave member at its desired position comprising servo control means utilizing position feedback from the slave shaft to position the slave shaft at the position indicated by the output of the memory device, and feed forward velocity control means or positioning the slave shaft as a function of the rate of change of the sequentially changing digital signal and the required change in slave shaft position.

12. Position control apparatus as claimed in claim 11 comprising:

digital comparing means for storing and comparing the present desired digital position of a slave shaft and the preceding desired digital position of a slave shaft to determine the required change in slave shaft position; and

roll over compensating means for providing correct computation of the required change in slave shaft position when a zero transition occurs between the preceding and present digital slave shaft position.