SMA Haptic Assembly Control for Fast Actuation With Smaller Capacitors
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Solution Overview
Problem
Existing SMA haptic assemblies in mobile devices face challenges in delivering high power quickly enough to produce tactile feedback without requiring large capacitors, which are physically impractical and inefficient.
Innovation Solution
A method of driving SMA haptic assemblies by dividing the heating process into a pre-heating period and an actuation period, allowing for different power profiles and reducing the strain on the power supply, using a combination of current source and capacitive element to optimize energy delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a capacitor circuit is used to provide sustained power output for SMA actuation, then the power delivery capability is improved, but the device size becomes too large for mobile devices
Solution Approach 1:
The heating process is divided into two distinct phases: a pre-heating period at lower power to raise the SMA temperature接近 the transition point, and an actuation period at high power to complete the phase transition. This segmentation allows the capacitor to be smaller because it only needs to supply energy during the brief actuation period, not the entire heating process.
Solution Approach 2:
The pre-heating period performs preliminary action by raising the SMA temperature close to the transition point before the actual actuation. This preliminary heating reduces the energy that needs to be delivered during the actuation period, allowing for a smaller capacitor while still achieving rapid actuation.
2Speed
If high power is delivered to the SMA to achieve rapid actuation, then the haptic response time is improved, but the battery cannot sustain the required power output
Solution Approach 1:
The system uses periodic action by alternating between a low-power pre-heating phase and a high-power actuation phase. The pre-heating phase prepares the SMA over a longer period at lower power, enabling the subsequent actuation phase to deliver high power for rapid response without requiring the battery to sustain high power continuously.
Solution Approach 2:
The power delivery parameters are changed over time: initially delivering lower power during pre-heating, then switching to high power during actuation. This dynamic parameter change allows the battery to meet the high power demand during actuation while maintaining sustainable average power consumption.
3Loss of time
If the SMA is heated as fast as possible to provide haptic feedback, then the response time is improved, but the design flexibility of other components is reduced
Solution Approach 1:
By segmenting the heating process into pre-heating and actuation phases with different power levels, the system maintains fast haptic response during actuation while allowing greater design flexibility during the pre-heating phase. Other components can be optimized for the lower power pre-heating conditions while still achieving rapid actuation when needed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient and rapid actuation of SMA haptic assemblies, reducing the need for large capacitors and minimizing energy consumption while maintaining a satisfactory haptic experience.
Implementation Method 1
the SMA must be heated until it makes a transition between two crystalline states
Implementation Method 2
the contraction of an SMA wire to cause relative motion of two components. The SMA wire is in contact with parts of two opposing bodies which are forced apart due to the change in length of the SMA wire as it contracts
Implementation Method 3
supplying drive current to the actuator successively during a pre-heating period in which the temperature of the shape memory alloy is raised
Data Source
AI summary
There is provided a method of driving a shape memory alloy haptic assembly comprising an actuator comprising shape memory alloy that is arranged on actuation to provide a haptic effect, the method comprising supplying drive current to the actuator successively during a pre-heating period in which the temperature of the shape memory alloy is raised without causing the shape memory alloy to provide the haptic effect and during an actuation period in which the temperature of the shape memory alloy is raised so as to cause the shape memory alloy to provide the haptic effect. A shape memory alloy haptic assembly is also provided.