Button providing force sensing and/or haptic output

1. A module, comprising:

a permanent magnet biased electromagnetic haptic engine, comprising:

a first stator;

a second stator; and

a rotor sandwiched between the first stator and the second stator;

a constraint coupled to the first stator and the rotor; and

a force sensor at least partially attached to the permanent magnet biased electromagnetic haptic engine and configured to sense a force applied to the rotor; wherein:

the constraint is configured to,

constrain closure of a pair of gaps between the rotor and the first stator, and between the rotor and the second stator, and bias the rotor toward a rest position in which the rotor is separated from the first stator and the second stator by the pair of gaps; and

cause the rotor to move about an axis of the constraint when the rotor is moved by the permanent magnet biased electromagnetic haptic engine.

2. The module of claim 1 , wherein the rotor comprises:

a core;

at least one coil wound around the core; and

at least one permanent magnet on a surface of the core.

3. The module of claim 1 , further comprising a button, mechanically coupled to the permanent magnet biased electromagnetic haptic engine.

4. The module of claim 3 , wherein the button is mechanically coupled to the rotor.

5. The module of claim 3 , wherein the constraint is attached to the permanent magnet biased electromagnetic haptic engine along the axis of the constraint, and the axis of the constraint is disposed on a same side of the rotor as the button.

6. The module of claim 3 , wherein the constraint is attached to the permanent magnet biased electromagnetic haptic engine along the axis of the constraint, and the axis of the constraint is disposed on a side of the rotor opposite the button.

7. The module of claim 1 , wherein the constraint comprises a metal flexure having rotor attachment portions on either side of a stator attachment portion.

8. The module of claim 1 , wherein the constraint comprises an elastomer disposed between the first stator and the rotor.

9. The module of claim 1 , wherein the force sensor comprises a capacitive force sensor.

10. The module of claim 1 , wherein the force sensor comprises a strain sensor.

11. A module, comprising:

a haptic engine having a movable portion sandwiched between a first stationary portion and a second stationary portion, the movable portion configured to move non-linearly when the haptic engine is stimulated by an electrical signal;

a force sensor at least partially attached to the haptic engine and configured to sense a force applied to the module; and

a constraint configured to constrain movement of the movable portion relative to the first stationary portion and the second stationary portion and bias the movable portion toward a rest position in which the movable portion is separated from the first stationary portion and the second stationary portion by a pair of gaps.

12. The module of claim 11 , wherein the constraint is configured to provide a first stiffness opposing the non-linear movement of the movable portion.

13. The module of claim 11 , further comprising:

a button attached to the movable portion of the haptic engine; wherein:

the force applied to the module comprises a force applied to the button; and

the constraint is configured to provide a second stiffness opposing a force applied to the button.

14. The module of claim 11 , wherein the constraint constrains movement of the movable portion to movement about a pivot axis.

15. The module of claim 11 , wherein the constraint comprises an elastomer.

16. The module of claim 11 , wherein the constraint comprises a metal flexure.

17. A method of providing a haptic response to a user, comprising:

using a flexure attached to a haptic engine along an axis to,

constrain relative motion between a stationary portion and a movable portion of the haptic engine;

bias the movable portion toward a rest position in which the movable portion is separated from the stationary portion by a gap; and

constrain closure of the gap;

determining a force applied to a button using a force sensor, the button mechanically coupled to the movable portion;

determining the determined force matches a predetermined force;

identifying a haptic actuation waveform associated with the predetermined force; and

applying the haptic actuation waveform to the haptic engine; wherein:

the application of the haptic actuation waveform to the haptic engine causes the movable portion of the haptic engine to move non-linearly about the axis along which the flexure is attached to the haptic engine.

18. The method of claim 17 , wherein:

the force sensor comprises at least two force sensing elements positioned at different locations relative to a user interaction surface of the button;

the force is determined using different outputs of the different force sensing elements;

determining the force comprises determining an amount of force; and

determining the determined force matches the predetermined force comprises determining the determined amount of force matches a predetermined amount of force.

19. The method of claim 17 , wherein:

the force sensor comprises at least two force sensing elements positioned at different locations relative to a user interaction surface of the button;

the force is determined using different outputs of the different force sensing elements;

determining the force comprises determining a force location; and

determining the determined force matches the predetermined force comprises determining the determined force location matches a predetermined force location.

20. The method of claim 17 , wherein:

determining the force comprises determining a force pattern; and

determining the determined force matches the predetermined force comprises determining the determined force pattern matches a predetermined force pattern.