Closed-loop control of linear resonant actuator using back EMF and inertial compensation

Patent metadata

Field	Value
Publication number	US-10601355-B2
Application number	US-201816147434-A
Country	US
Kind code	B2
Filing date	Sep 28, 2018
Priority date	Sep 29, 2017
Publication date	Mar 24, 2020
Grant date	Mar 24, 2020

Abstract

A system for providing closed-loop control of a linear resonant actuator using Back Electromotive Force (EMF) and inertial compensation is disclosed. In an embodiment, one or more inertial sensors are used to estimate low frequency motion of a haptic engine moving mass and compensate for the motion using a feedforward model, thus providing a more robust closed-loop control system for controlling the moving mass when subjected to low frequency disturbances by a user, for example, shaking or swinging the device.

First claim

What is claimed is:

1. A system comprising:
a linear resonant actuator (LRA) including a frame, one or more coils mounted to the frame and operable to generate a magnetic field, and a mass including magnetic portions positioned within the frame and configured to move within the frame along a movement axis;
drive electronics coupled to the linear resonant actuator (LRA) and to the one or more coils;
one or more inertial sensors;
a closed-loop controller coupled to the one or more inertial sensors and the drive electronics, the controller configured to:
estimate a coil resistance of the one or more coils;
compute an estimated linear acceleration of the mass based on signals from the one or more inertial sensors;
compute a disturbance rejection feedforward compensation signal based on the estimated linear acceleration, the estimated coil resistance and a motor constant;
compute a position feedforward compensation signal based on a reference position of the mass;
compute an estimated velocity of the moving mass based on output signals of the drive electronics and the estimated coil resistance;
compute an actuator control signal based on a difference between the estimated mass velocity and a reference mass velocity;
compute a compensated actuator control signal by compensating the actuator control signal with the disturbance rejection feedforward compensation signal and the position feedforward compensation signal; and
provide the compensated actuator control signal to the drive electronics, the compensated actuator signal causing the drive electronics to adjust coil current in the one or more coils.

2. The system of claim 1 , wherein the one or more coils are mounted to the mass and the magnetic portions are mounted to the frame.

3. The system of claim 1 , wherein the one or more inertial sensors include at least one accelerometer.

4. The system of claim 1 , wherein the LRA includes one or more temperature sensors and the coil resistance is computed from temperature readings provided by the one or more temperature sensors.

5. The system of claim 4 , wherein the LRA includes one or more magnetic sensors and the temperature readings are derived from signals output by the one or magnetic sensors in the LRA.

6. The system of claim 1 , wherein the estimated linear acceleration is filtered using a low-pass filter to remove low frequency disturbances.

7. The system of claim 1 , further comprising:
a frequency shaping module configured to receive a gain adjusted reference position and output a band-limited position feedforward compensation signal.

8. The system of claim 1 , wherein the controller is configured to implement a state observer for computing the estimated mass velocity based on a coil voltage, the coil current, the estimated coil resistance and the compensated actuator control signal.

9. The system of claim 1 , wherein the output signals from the drive electronics include a measurement of the coil current.

10. The system of claim 1 , wherein computing the compensated actuator control signal includes compensating the actuator control signal with the disturbance rejection feedforward compensation signal, the position feedforward compensation signal and a resistance tone.

11. A method comprising:
estimating, by a closed-loop controller, a coil resistance for one or more coils of a linear resonant actuator (LRA);
computing, by the closed-loop controller, an estimated linear acceleration of a mass in the LRA based on signals from one or more inertial sensors;
computing, by the closed-loop controller, a disturbance rejection feedforward compensation signal based on the estimated linear acceleration, the estimated coil resistance and a motor constant;
computing, by the closed-loop controller, a position feedforward compensation signal based on a reference position of the mass;
computing, by the closed-loop controller, an estimated velocity of the moving mass based on output signals of drive electronics coupled to the one or more coils, and the estimated coil resistance;
computing, by the closed-loop controller, an actuator control signal based on a difference between the estimated mass velocity and a reference mass velocity;
computing, by the closed-loop controller, a compensated actuator control signal by compensating the actuator control signal with the disturbance rejection feedforward compensation signal and the position feedforward compensation signal; and
providing, by the closed-loop controller, the compensated actuator control signal to the drive electronics, the compensated actuator signal causing the drive electronics to adjust coil current in the one or more coils.

12. The method of claim 11 , wherein the one or more coils are mounted to the mass and magnetic portions are mounted to a frame of the LRA.

13. The method of claim 11 , wherein the one or more inertial sensors include at least one accelerometer.

14. The method of claim 11 , wherein temperature readings are provided by a temperature sensor in the LRA.

15. The method of claim 11 , wherein temperature readings are derived from signals output by one or magnetic sensors in the LRA.

16. The method of claim 11 , wherein the estimated linear acceleration is filtered using a low-pass filter to remove low frequency disturbances.

17. The method of claim 11 , further comprising:
a frequency shaping module configured to receive a gain adjusted reference position and output a band-limited position feedforward compensation signal.

18. The method of claim 11 , wherein the closed-loop controller is configured to implement a state observer for computing the estimated mass velocity based on a coil voltage, the coil current, the estimated coil resistance and the compensated actuator control signal.

19. The method of claim 11 , wherein the output signals from the drive electronics include a measurement of the coil current.

20. The method of claim 11 , wherein computing the compensated actuator control signal includes compensating the actuator control signal with the disturbance rejection feedforward compensation signal, the position feedforward compensation signal and a resistance tone.

Assignees

• Apple Inc

Inventors

• Vasudevan Hari
• Mazzochette Eileen A
• Hajati Arman
• Yoneoka Shingo

Classifications

• H02P23/14

  Estimation or adaptation of motor parameters, e.g. rotor time constant, flux, speed, current or voltage · CPC title

• H02K33/18

  with coil systems moving upon intermittent or reversed energisation thereof by interaction with a fixed field system, e.g. permanent magnets · CPC title

• H02K29/08

  using magnetic effect devices, e.g. Hall-plates, magneto-resistors (H02K29/12 takes precedence) · CPC title

• H02P23/12

  Observer control, e.g. using Luenberger observers or Kalman filters · CPC title

• H02P25/034 Primary

  Voice coil motors (voice coil motors driven by DC H02P7/025) · CPC title