Input Devices (Touch Pads, Electrodes, Linear Transducer, Switches)

Remote Myoelectrodes Touch Pads™ Linear Transducers Switches In-Socket Myoelectrodes

Input devices are like translators that communicate the user’s wishes to the motors of the prosthesis. We offer a variety of input devices, because different users have different abilities. Myoelectrodes pick up the signals generated by muscle contractions, whereas Touch Pads, Servo Transducers, and Switches are all actuated by movement of the residual limb. The choice of input device depends not only on the user’s abilities, but also on the device being controlled, and the type of control circuit.

In many cases, the user may be able to use more than one input device. If this is true, then the convenience of the patient should be the deciding factor. For example, if the residual limb has good muscle sites, myoelectrodes are often the best choice because they are convenient and usually require less training. If the limb does not have good muscle sites, one of the other input devices might better suit the patient’s needs.

Myoelectrodes can regulate both the speed and the direction of the prosthesis. The speed is directly proportional to the strength of the input muscle signal. Proportional speed gives the most precise control of a prosthesis.

Touch Pads™ are pressure-sensitive pads that adhere to the inside of the socket. As their name implies, Touch Pads are operated by touch. The user simply moves the residual limb to push lightly on the Touch Pad to operate the prostheses. These input devices are a cost-effective alternative to myoelectrodes. Like myoelectrodes, Touch Pads provide proportional speed control, since the amount of pressure applied determines the speed of the prosthesis. Touch Pads are normally supplied in a ¾” diameter, but are also available in smaller and larger sizes.

LTI Linear Transducer Linear Transducers turn relative body motion into electrical signals. The LTI Transducer generates an electric voltage that increases from zero to maximum as the cord on the unit is pulled either a half inch (13mm) or an inch (26mm). The voltage looks the same as the varying voltage from a typical electrode amplifier and can be used in the same way. However, the preferred use is with a positional servo circuit. With it the user controls the position of the prosthetic joint by controlling how far the transducer is pulled. Thus body motion translates directly into prosthetic joint motion. If the users pulls the transducer a half-inch (full excursion), the prosthesis goes through its full range of motion. A smaller movement of the transducer produces a smaller movement of the prosthesis. The user’s abilities determine what body movement is used to actuate the Linear Transducer. A typical arrangement is to mount the Linear Transducer into the prosthetic support harness, so that chest expansion moves the transducer and results in movement of the prosthesis. Users can accurately position the prosthesis with these transducers. The circuits used with these transducers usually contain a sleep circuit. By pausing, the user can leave the prosthesis in a fixed position. Linear Transducers provide proportional speed control.

Switches, a more basic option, are available in various styles. Switches command the prosthesis motors to operate in one direction or the other at a fixed speed. Switches do not provide proportional control; they simply turn the motors on or off. Dual action switches control motion in two directions. With a simple switch to do device selection a dual action switch can be used to operate multiple devices. Switches are usually incorporated into the harness, but each mounting configuration is slightly different.

Additional Information Product Catalog: Input Devices (PDF) Linear Transducer Instructions (PDF) Promotional Information: Remote Electrodes - Boston Arm (PDF) Remote Electrodes - DC (PDF)