Home

C-tactile Robotic Brusher

Background:

Dr. Laura Case is currently researching C-tactile afferents with the UCSD School of Medicine, sponsored by the National Institute of Health. C-tactile afferents are nerve fibers primarily found under hairy skin such as the forearm that researchers believe are responsible for feelings of pleasure and pain. Previous lab experiments were performed by research assistants who were trained to manually brush patients' arms. The project seeks to replicate and automate human brushing.

Objectives:

The primary objective of this project is to replicate the pleasant sensations generated by manual brushing. To achieve stimulation of the C-tactile afferents, a specific set of parameters is required of the brusher. These are: a brushing force of 0.3 - 0.4 N and brushing speeds of 3 cm/s and 30 cm/s over a length of 12 cm.

Ideally, the device will minimize noise and vibrations to isolate the effects of these nerve fibers.

This device will be used by Dr. Laura Case and the UCSD School of Medicine for use in patient trials.

Final Design:

The final design for the robotic brusher uses a series of brushes mounted to a motor driven belt and pulley system. Mounting multiple brushes allows for truly continuous brushing of the arm as they are spaced so when a brush finishes the 12 cm long stroke, another brush immediately makes contact with the arm. The brushes are attached to the belt through a 3D printed brush holder that clamps onto the bristles and is attached to the belt via wires.

The size of the belt-pulley system is made minimal and then mounted on top of a larger frame that supports the brushing sub assembly. This design serves to increase the modularity of the device and allow Dr. Case to detach the brusher for potential future use in other projects. The arm support subassembly is also attached to the lower frame. This modified lab jack allows for adjustment of the patient's arm vertically, and at an angle with respect to the horizontal in order to get the top of the arm parallel to the brushing path.

Left: Skeleton View of Belt and Pulley Systems, Right: Full Assembly Including Arm Support and Casing

Other Side of Full Assembly including Casing

Performance Results:

The primary means of determining performance will be to measure the pressure and speed of the brush stroke to ensure they fulfill the functional requirements defined.

For the speed of the brush stroke, the output will be verified through video replay to ensure that the brush extension satisfies the 3 cm/s and 30 cm/s speeds. The speed will be additionally verified through motor encoders used to measure the speed of the motor, which can be used to calculate the speed of the brush.

The force of the brush stroke will be measured by using a standard postage scale. The brush stroke will be measured at the start, middle, and end of the brush stroke to ensure that a uniform 0.3-0.4 N is applied throughout the full brush stroke.

Robustness of the robotic brusher will be tested by running the brushing subsystem continually for 10 minutes on 3 cm/s and for 5 min on 30 cm/s for multiple trials. Satisfactory performance is defined as continual brushing for the full time period without need for adjustment and passing of the first speed and force tests at the end of the period.

The final performance results are included below:

The robotic brusher is capable of operating at 30 cm/s and 3 cm/s without difficulty. The device can operate for over 10 minutes at 30 cm/s without stalling or overheating from the motor. The brush stroke has been described as seemingly continuous and qualitatively pleasant by all members of the team. The arm jack is comfortable and can easily be adjusted to meet the required uniform force. Noise is negligible, with the only noteworthy sound being a light hum from the motor. Vibration is also negligible and does not impact the overall enjoyability of using the device.