Retractable Head Pointer

Designers: Alexei Kambalov
Client Coordinators: Judy Stroupe, Antonia Pedroza
Supervising Professor: Dr. Larry N. Bohs

The client has cerebral palsy, no use of his right arm, and only limited use of his left arm. His job involves moving, sorting, and otherwise manipulating small, light objects such as sheets of paper, plastic tags, and pens. Currently, this is accomplished with his left arm, with considerable difficulty. Because he has good head control, we designed a cap-mounted pointer. In contrast to most commercial products, this device uses a small and relatively unobtrusive mounting system. An electric motor, mounted to the client’s wheelchair, extends and retracts the pointer.  The user controls the telescoping pointer using a single lever switch.

How this project helped
After 2 months of use, Antonia Pedroza, one of the client’s supervisors, remarks that, “The head pointer allows an individual who is really interested in working do more jobs. The head pointer allows this person to work with paper, something he was not able to do before without destroying the paper.”  His other supervisor, Judy Stroupe, comments, “The head pointer has enabled a gentleman to perform his work independently and the smile on his face says it all.”

The Retractable Head Pointer, shown in Figure 1, uses a commercial automotive power antenna for both the motor and the pointer.  The motor uses 12V power from the client’s wheelchair battery. To allow for a full range of relative motion, a length of vinyl tubing is inserted between the motor and the antenna, housing the motor-to-antenna controlling cable. The tubing is attached to the motor, on one end, and to the antenna, on the other, with compression fittings. This allows the tubing to be removed and replaced easily.

The original motor control circuitry was removed, leaving only a DC motor whose direction of rotation was easily controlled. This control is accomplished by varying the polarity of the voltages of the power leads, using a SPDT switch with a long lever. The circuit uses two DPST relays to isolate the switch itself from the motor current, which can reach 1.5A. A 2A fuse between the control circuit and the battery provides short circuit protection.

Figure 2 shows the pointer mounted to the client and his wheelchair. Two modified binder clips attach the pointer to the client’s hat. The clip attached to the bill of the cap uses a piece of heat-shrink tubing, while the clip at the back of the hat holds an eye bolt that extends slightly outward. The positioning of the attachment points provides optimal position of the pointer relative to the head. Padding at the rear attachment point maximizes comfort.  A spring mechanism connects the motor to the wheelchair to improve range of motion (see Figure 1).

Electrical connectors attach at three points: the battery, the control box, and the motor. To ensure that no chance for confusion exists, each point uses a different type of plug and jack; interlocks within the connectors prevent misconnection. The battery cable connects to the main cable via an axial 2-lead jack. The main cable plugs into the control box with a 6-lead plug. Finally, the control cable connects to the motor with a 4-lead plug. All connectors are easy-off, protecting the components from accidental jerks.

The pointer tip consists of a piece of soft rubber cut in a cross shape and wrapped around the end of the antenna. The rubber is held in place with a cable tie.  This design provides excellent friction for moving sheets of paper and for other manipulation, and is very inexpensive and easy to replace.

The cost of parts for the project was $120.

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