Chasm Is a Compact Haptic Actuator Based on a Leadscrew and DC Motor

The linear actuator offers expressive haptic feedback to enhance human-computer interaction in virtual and augmented environments.

Cabe Atwell
4 years agoWearables / 3D Printing
Chasm renders expressive haptic feedback on wearable and handheld devices. (📷: Preechayasomboon et al)

A new development in human-computer interaction, Chasm is a compact linear actuator designed to render expressive haptic feedback on wearable and handheld devices. Chasm is a screw-based actuator that uses screw drives to directly convert the high rotational speed of a motor to linear motion without requiring an intermediate transmission mechanism.

The core of the actuator is a motor coupled directly to a leadscrew. This design employs a minimal number of components: a DC motor without an integrated gearhead, a custom leadscrew and nut, two bearings, and a housing. A proportional-integral (PI) feedback control law is used to maintain high bandwidth and reduced finger loading effects. The resulting compact haptic actuator is usable in a variety of wearable and handheld configurations.

The position of the leadscrew is tracked via a magnetic encoder placed directly underneath the leadscrew assembly. Closed-loop control is achieved by reading the magnetic encoder as an input and sending correction commands to the motor driver. In testing, a microcontroller was used to maintain an interrupt-driven 1000 Hz proportional-integral controller on up to two Chasm units. The gains of the controller are selected to compensate for skin-loading disturbance and reduce structural and resonant harmonics.

A robust software framework enables Chasm units to adapt to various scenarios and use cases. The USB HID device class is used for communication between the rendering device and the microcontroller due to two major benefits: plug-and-play capability for most gadgets on the market and that it requires the host device to reserve bandwidth for HID. Protocol buffers are used as a serialization layer to increase scalability and aid development time.

Compared to other devices, Chasm has broad bandwidth, achieved through the use of smaller and fewer components and optimization of the actuator response through a PI feedback control law. It’s small casing also allows it to be directly integrated into a variety of hardware with relative ease. The actuator can even be configured to exert force in multiple directions. Typically, it can be used to shear or stretch skin by sliding against it, but the addition of a coupling adaptor can translate the carriage motion to indent the skin.

Applications include handheld devices, where Chasm’s linear motion is interfaced with the palm or fingers, such as in a controller or cellphone case, or wearable devices where the actuator stretches the skin to provide haptic cues. The device is configured to be lightweight, compact, and scalable such as to provide feedback in multiple applications. Currently, the device has been tested in a headband to provide haptic cues at the temples and a handheld pointing device to enhance interaction between a user and virtual objects. Still, the research team envisions future work to determine Chasm’s capacity in other wearable devices.

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