# US 2019/0317136 A1 · Sensing motor current

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 2019/0317136 A1
- Document ID: US20190317136A1
- Status: Published application
- Kind: A1
- Application number: 16/465,650
- Filed: 2017-12-01
- Published: 2019-10-17
- Earliest claimed: 2016-12-02
- Assignees: Cmr Surgical Limited
- Applicants: Cmr Surgical Limited
- Inventors: Paul Christopher Roberts; Edward John Mottram
- Web page: https://patentgrep.com/patent/US20190317136A1

## CPC

- G01R 15/202: {using Hall-effect devices (Hall elements in arrangements for measuring electrical power G01R21/08)}
- G01R 19/32: Compensating for temperature change
- G01R 33/0005: {Geometrical arrangement of magnetic sensor elements; Apparatus combining different magnetic sensor types (G01R33/0206 takes precedence)}
- G01R 33/0017: {Means for compensating offset magnetic fields or the magnetic flux to be measured; Means for generating calibration magnetic fields}
- G01R 33/0076: {Protection, e.g. with housings against stray fields}
- G01R 33/0082: {Compensation, e.g. compensating for temperature changes}
- G01R 35/00: Testing or calibrating of apparatus covered by the other groups of this subclass
- H02P 6/28: Arrangements for controlling current (H02P6/10 takes precedence)
- H02P 21/22: Current control, e.g. using a current control loop
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- H02P: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS

## 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.

## Claims

### Claim 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.

### Claim 2 (depends on 1)

A 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.

### Claim 3 (depends on 1)

A 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.

### Claim 4

(canceled)

### Claim 5 (depends on 1)

A 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.

### Claim at position 6

-8. (canceled)

### Claim 9 (depends on 1)

A 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.

### Claim 10 (depends on 1)

A 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.

### Claim 11 (depends on 10)

A circuit as claimed in claim 10, further comprising a temperature sensor configured to measure the circuit temperature, and output a measured circuit temperature to the controller.

### Claim 12 (depends on 11)

A circuit as claimed in claim 11, 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.

### Claim 13 (depends on 12)

A circuit as claimed in claim 12, 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.

### Claim 14 (depends on 13)

A circuit as claimed in claim 13, 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.

### Claim 15 (depends on 12)

A circuit as claimed in claim 12, 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.

### Claim 16 (depends on 12)

A circuit as claimed in claim 12, 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.

### Claim 17 (depends on 12)

A circuit as claimed in claim 12, 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.

### Claim 18 (depends on 1)

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

### Claim 19 (depends on 18)

A circuit as claimed in claim 18, wherein the magnetic shield comprises two shield layers arranged on either side of the current sensors.

### Claim 20 (depends on 18)

A circuit as claimed in claim 18, wherein the magnetic shield comprises a further shield element located between the motor and the current sensors.

### Claim at position 19

-22. (canceled)