Integrated planar SMA device and method
This disclosure relates generally to a reusable actuating device utilizing multiple integrated planar shape memory alloy elements integrated with independent driver circuits and at least one return spring integrated onto a single multi-layer PCB with a novel layout to create an electrically and mechanically redundant integrated actuator solution uniquely suited for use in low-profile devices that can be utilized by themselves or as an initiator in a staged device to release higher loads. The apparatus of the invention is particularly useful for spacecraft and other vehicular actuation devices.
1 . An integrated planar shape memory alloy (SMA) device, comprising:
a multi-layer printed circuit board (PCB);
SMA elements;
an output latch;
bridge components;
a return spring; and
driver circuits;
where said SMA elements, said output latch, said bridge components, said return spring and said driver circuits are mounted on said PCB, and wherein said SMA elements cause said output latch to actuate when a current is applied to said SMA elements,
wherein said integrated planar SMA device mounts in a housing having a secondary output latch connected by a secondary spring,
and wherein said secondary output latch connects said output latch;
and
wherein said secondary output latch is pressed against said output latch with the help of said secondary spring to press said output latch causing said SMA elements to heat to or beyond their transition temperature by current applied through said driver circuits.
2 . The integrated planar SMA device of claim 1 , wherein said output latch is split into at least two output latch halves to mount said PCB and to capture said return spring between said two output latch halves and said bridge components.
3 . The integrated planar SMA device of claim 2 , wherein said bridge components comprise bridge wires and bridge plates.
4 . The integrated planar SMA device of claim 3 , wherein said bridge plates clamp fixed ends of said SMA elements to said PCB fixing them and causing them to contact conductive patches which in turn connect said SMA elements to said driver circuits.
5 . The integrated planar SMA device of claim 3 , further comprises end-of-travel pins, wherein said end-of-travel pins attach to said PCB, and wherein said bridge wires attach to said output latch halves.
6 . The integrated planar SMA device of claim 1 , wherein said SMA elements are collocated with said PCB such that each SMA element of said SMA elements is a mirror of the other, resulting in two SMA elements that retract the same amount when heated to their transition temperature electrically through said driver circuits and actuate said output latch.
7 . The integrated planar SMA device of claim 2 , wherein said return spring is pre-compressed to a predetermined load and sized such that said return spring applies a nearly constant load to said SMA elements during cooling to re-stretch said SMA element to its original length, causing said integrated planar SMA device to reset itself once power is no longer applied or once said driver circuits are in a latched state.
8 . The integrated planar SMA device of claim 2 , wherein said return spring sits in a cut-out in said PCB such that said return spring pushes said output latch halves tensioning said SMA elements.
9 . The integrated planar SMA device of claim 3 , wherein said SMA elements are heated to or beyond their transition temperature by current applied through said driver circuits.
10 . The integrated planar SMA device of claim 9 , wherein said output latch halves retract due to the force exerted by said SMA elements when said SMA elements reach their transition temperature.
11 . The integrated planar SMA device of claim 9 , wherein said bridge wires contact end-of-travel pins attached to said PCB and close a switching circuit in said driver circuits and cut power to said SMA elements to prevent annealing.