Resonant actuator assembly
A resonant actuator assembly ( 1 ) comprising: a support structure ( 3 ); a movable part ( 5 ) that is capable of relative motion with respect to the support structure; and an actuator arrangement ( 7 ) arranged to drive relative motion of the movable part, the resonant actuator assembly being arranged to provide a restoring force to the movable part on displacement from an equilibrium position with respect to the support structure, and the actuator arrangement being arranged to drive the relative motion of the movable part at a resonance of the resonant actuator assembly, the restoring force being non-linear with the displacement.
1 . A resonant actuator assembly comprising:
a support structure;
a movable part that is capable of relative motion with respect to the support structure; and
an actuator arrangement arranged to drive relative motion of the movable part at a resonance of the resonant actuator assembly,
the resonant actuator assembly being arranged to provide a restoring force to the movable part with a stiffness that increases when a magnitude of displacement of the movable part from an equilibrium position with respect to the support structure increases, so as to flatten a histogram of position against time over the resonance period compared to an equivalent system where the restoring force has a constant stiffness, and the actuator arrangement being arranged to drive the relative motion of the movable part at a resonance of the resonant actuator assembly, the restoring force being non-linear with the displacement.
2 . The resonant actuator assembly according to claim 1 , wherein the actuator arrangement comprises at least one SMA wire and the actuator assembly further comprises a drive circuit arranged to supply drive signals to the at least one SMA wire, and wherein the drive signals comprises pulses at a resonant frequency of the resonance.
3 . The resonant actuator assembly according to claim 2 , wherein the at least one SMA wire is inclined at an acute angle with respect to a movement axis of the relative motion of the movable part.
4 . The resonant actuator assembly according to claim 2 , wherein the resonant actuator assembly further comprises at least one intermediate part that is capable of relative motion with respect to the support structure and the movable part, and
the actuator arrangement comprises plural stages of at least one SMA wire each arranged to drive relative motion between two parts of the support structure, the at least one intermediate part and the movable part in mechanical series so as to additively drive the relative motion of the movable part with respect to the support structure.
5 . The resonant actuator assembly according to claim 2 , wherein the actuator arrangement comprises opposed SMA wires arranged to drive the relative motion of the movable part in opposite directions along a movement axis, wherein the opposed SMA wires are inclined at an acute angle so as to provide components of force perpendicular to the movement axis in the same direction.
6 . The resonant actuator assembly according to claim 2 , wherein the actuator arrangement comprises at least one SMA wire arranged to drive the relative motion of the movable part in a first direction along a movement axis and no SMA wires arranged to drive the relative motion of the movable part in a second direction opposite to the first direction.
7 . The resonant actuator assembly according to claim 2 , wherein the resonant frequency is at least 10 Hz, and/or
wherein the range of displacement is at least 10 μm.
8 . The resonant actuator assembly according to claim 1 , wherein the actuator arrangement comprises opposed pairs of SMA wires, the SMA wires of each pair being inclined at equal and opposite acute angles with respect to the movement axis of the relative motion of the movable part so as to provide balanced components of force perpendicular to the movement axis.
9 . The resonant actuator assembly according to claim 1 , wherein the resonant actuator assembly further comprises a resilient element connected between the movable part and the support structure, and arranged to provide at least part of said restoring force.
10 . The resonant actuator assembly according to claim 1 , further comprising a bearing arrangement arranged to guide relative motion of the movable part with respect to the support structure, wherein the bearing arrangement is arranged to provide no restoring force, or
wherein the bearing arrangement is arranged to provide a restoring force that is at least an order of magnitude less than the restoring force provided by the actuator arrangement, or wherein the bearing arrangement is arranged to provide a restoring force that is at least an order of magnitude more than the restoring force provided by the actuator arrangement.
11 . The resonant actuator assembly according to claim 1 , further comprising a position detection circuit arranged to derive a measure of the relative position of the movable part with respect to the support structure,
wherein the resonant actuator assembly further comprises a position sensor arranged to sense the relative position of the movable part from the position sensor, and the position detection circuit is arranged to derive the measure of the relative position of the movable part from the output of the position sensor, or
wherein the actuator arrangement comprises at least one SMA wire, the resonant actuator assembly further comprises a resistance measurement circuit arranged to measure the resistance of the at least one SMA wire, and the position detection circuit is arranged to derive the measure of the relative position of the movable part from the output of the measured resistance.
12 . The resonant actuator assembly according to claim 1 , wherein the movable part is an optical component, and
wherein the resonant actuator assembly is arranged to scan a beam of light.
13 . The resonant actuator assembly according to claim 1 , wherein the resonant actuator assembly is arranged to provide the restoring force with an increase in stiffness when a magnitude of the displacement from the equilibrium position increases above a predetermined threshold.
14 . The resonant actuator assembly according to claim 13 , wherein the resonant actuator assembly comprises a resilient bumper between the movable part and the support structure, the resilient bumper being arranged to be disengaged when the magnitude of the displacement from the equilibrium position is below the predetermined threshold and to be engaged to provide the restoring force with the increase in stiffness when the magnitude of the displacement from the equilibrium position increases from the predetermined threshold.
15 . A resonant actuator assembly comprising:
a support structure;
a movable part that is capable of relative motion with respect to the support structure; and
an actuator arrangement comprising at least one SMA wire arranged to drive the relative motion of the movable part, wherein the at least one SMA wire is inclined at an acute angle with respect to a movement axis of the relative motion of the movable part,
the resonant actuator assembly being arranged to provide a restoring force to the movable part on displacement from an equilibrium position with respect to the support structure, and the actuator arrangement being arranged to drive the relative motion of the movable part at a resonance of the resonant actuator assembly.
16 . A system comprising:
a sensor for sensing light, the sensor being configured to provide data dependent on the sensed light; and
a resonant actuator assembly comprising:
a support structure;
a movable part that is capable of relative motion with respect to the support structure; and
an actuator arrangement arranged to drive the relative motion of the movable part over a movement range,
the resonant actuator assembly being arranged to provide a restoring force to the movable part on displacement from an equilibrium position with respect to the support structure, and the actuator arrangement being arranged to drive the relative motion of the movable part at a resonance of the resonant actuator assembly, the restoring force being substantially linear or non-linear with the displacement; and
wherein the sensor is configured to cease providing data when the movable part has moved within less than 10% of the movement range towards each end of the said movement range.
17 . The system according to claim 16 , wherein the sensor is configured to cease providing data when the movable part has moved within less than 8%, or less than 5%, of the movement range towards each end of the said movement range.
18 . The system according to claim 16 , wherein the system is a Time of Flight (TOF) system, comprising an illumination source for illuminating a subject, wherein the sensor is configured to sense light scattered by the subject, and wherein the movable part having an optical component for focusing or reflecting illumination onto the subject.