Sensing motor current

Patent metadata

Field	Value
Publication number	US-10976353-B2
Application number	US-201716465650-A
Country	US
Kind code	B2
Filing date	Dec 1, 2017
Priority date	Dec 2, 2016
Publication date	Apr 13, 2021
Grant date	Apr 13, 2021

Abstract

A circuit for sensing the driving current of a motor, the circuit comprising: a driver configured to generate a driving current for each phase of a multiple-phase motor, the instantaneous sum of all the driving currents being zero; a current sensor for each phase of the multiple-phase motor, each current sensor configured to measure the driving current of that phase and comprising a plurality of current sensor elements arranged with respect to each other such that each current sensor element has the same magnitude of driving current systematic error due to magnetic fields external to the driving current to be measured; and a controller configured to, for each phase of the multiple-phase motor, generate an estimate of the driving current of that phase to be the measured driving current of that phase minus 1/n of the total of the measured driving currents for all phases, n being the number of phases of the multiple-phase motor.

First claim

The invention claimed is:

1. A circuit configured to sense the driving current of a multiple-phase motor, the circuit comprising:
a driver configured to generate the driving current for each phase of the multiple-phase motor, the instantaneous sum of all the driving currents being zero;
a current sensor for each phase of the multiple-phase motor, each current sensor configured to measure the driving current of that phase wherein each current sensor comprises two current sensor elements, each current sensor element configured to measure the driving current of the phase thereby generating a driving current reading, the measured driving current of that phase being a combination of the driving current readings of the current sensor elements, and the current sensor elements of each current sensor are arranged with respect to each other such that each current sensor element has the same magnitude of driving current systematic error due to magnetic fields external to the driving current to be measured; and
a controller configured to, for each phase of the multiple-phase motor, generate an estimate of the driving current of that phase to be the measured driving current of that phase minus 1/n of the total of the measured driving currents for all phases, n being the number of phases of the multiple-phase motor,
wherein the current sensor elements of each current sensor are arranged in an opposing orientation and are one of: (i) arranged back to back on a circuit board, and (ii) arranged side by side on a circuit board and wired in parallel.

2. The circuit as claimed in claim 1 , wherein the driver is configured to generate a succeeding driving current of each phase of the multiple-phase motor in response to a control input, the control input comprising the estimate of the driving current of each phase.

3. The circuit as claimed in claim 1 , wherein the controller is configured to generate an estimate of the error of each measured driving current to be equal to 1/n of the total of the measured driving currents for all phases.

4. The circuit as claimed in claim 1 , wherein the current sensor elements of each current sensor are arranged back to back on the circuit board and the controller is configured to calculate the measured driving current of that phase to be half the sum of the driving current readings of the two current sensor elements.

5. The circuit as claimed in claim 1 , wherein the current sensor elements of each current sensor are arranged side by side on the circuit board and wired in parallel and the controller is configured to calculate the measured driving current of the phase to be the sum of the driving current readings of the two current sensor elements.

6. The circuit as claimed in claim 1 , wherein each current sensor element is a Hall sensor configured to output a Hall voltage, the driving current reading being a function of the Hall voltage.

7. The circuit as claimed in claim 6 , further comprising a temperature sensor configured to measure the circuit temperature, and output a measured circuit temperature to the controller.

8. The circuit as claimed in claim 7 , wherein the controller is configured to:
receive a first calibration temperature measurement from the temperature sensor and a first calibration Hall voltage from a current sensor element of a phase of the multiple-phase motor, both measurements taken concurrently during circuit disconnection;
receive a second calibration temperature measurement from the temperature sensor and a second calibration Hall voltage from the said current sensor element, both measurements taken concurrently during circuit connection; and
derive a thermal calibration profile of the Hall voltage of the said current sensor element from the received calibration measurements.

9. The circuit as claimed in claim 8 , wherein the controller is configured to calibrate the measured driving current of a phase prior to generating an estimate of the driving current of that phase.

10. The circuit as claimed in claim 9 , wherein the thermal calibration profile is linear, and the controller is configured to calibrate the measured driving current of a phase by deducting a linear offset from each driving current reading of the current sensor elements of that phase in accordance with the thermal calibration profiles of those current sensor elements.

11. The circuit as claimed in claim 8 , wherein the controller is configured to receive the first calibration temperature measurement and the first calibration Hall voltage which were taken during circuit disconnection at start-up.

12. The circuit as claimed in claim 8 , wherein the controller is configured to receive the first calibration temperature measurement and the first calibration Hall voltage which were taken during a period of motor disconnection during use.

13. The circuit as claimed in claim 8 , wherein the controller is configured to receive the second calibration temperature measurement and the second calibration Hall voltage which were taken during circuit connection when the driving current of that phase was momentarily driven to zero by the driver following a period of higher driving current of that phase.

14. The circuit as claimed in claim 1 , further comprising a magnetic shield which encompasses all the current sensors.

15. The circuit as claimed in claim 14 , wherein the magnetic shield comprises two shield layers arranged on either side of the current sensors.

16. The circuit as claimed in claim 14 , wherein the magnetic shield comprises a further shield element located between the motor and the current sensors.

Assignees

• Cmr Surgical Ltd

Inventors

• Roberts Paul Christopher
• Mottram Edward John

Classifications

• H02P21/22

  Current control, e.g. using a current control loop · CPC title

• H02P6/28

  Arrangements for controlling current (H02P6/10 takes precedence) · CPC title

• G01R35/005

  Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references (G01R33/0035, G01R35/002 take precedence) · CPC title

• G01R35/00

  Testing or calibrating of apparatus covered by the other groups of this subclass · CPC title

• G01R33/0082

  Compensation, e.g. compensating for temperature changes · CPC title