Wrist-hand controller

For prosthetic arms to be more than just position controllers for portable vices, multifunctional mechanisms that have the ability to have multiple degrees of freedom controlled simultaneously (in parallel) in a subconscious manner need to be developed. Current commercially available multifunctional controllers are generally sequential in nature and take the form of two site, three state multifunctional controllers. Motion Control, Inc., in the ProControl hand-wrist controller, uses rapid cocontraction of the forearm extensors and flexors to switch control between hand opening and closing to wrist rotation. Otto Bock uses a similar control strategy in its wrist-hand controller. Motion Control, Inc., in its elbow controller, uses dwell time (parking) to switch from elbow flexion and extension to hand opening and closure and cocontraction of biceps and triceps to switch control from the hand back to elbow. 

Figure 1. The Zymate (Zymark Corp., Hopkinton, MA) showing the main robot module (center) with universal wrist and "gripper" hand attached. In the upper right is the controller with programming keyboard and soft keys (right hand side of display screen). The soft keys can be duplicated in a "teach/learn" pendant (not shown).

Bending the wrist excessively in any direction causes extreme pain. Use a wristlock when attacking this area. Place both your thumbs on the back of your opponent s hand. Bend the wrist at a right angle to his forearm (fig. 30). You can control your opponent when you get him in this position. 

Perhaps the most transparent (to the user) artificial arms are the ones that use electrical activity generated by the muscles remaining in the stump to control the actions of the elbow, wrist and hand [Stein et al., 1988]. This electrical activity is known as myoelectricity, and is produced as the muscle contraction spreads through the muscle. Note that these muscles, if intact, would have controlled at least... 

Externally powered prostheses use electrical power to provide function. The electrical power is applied via motors located in the terminal device (hand or hook), wrist, and elbow. The grip force of the hand can be in excess of 100 N. Command signals are generated either by voluntary contraction of muscles, so-called myoelectric control, or by using switches of different kinds. For apphcations that are more complex, both the command signals are used for different operations (e.g., control of several degrees of freedom). 

FIGURE 70.6 The Utah arm is a self-contained battery powered artificial arm-hand complex. The system comprises myoelectric control of the elbow, wrist, and grasping movements. 

With the expanded use of computers, keyboards have become extremely common control and data entry devices. There are many different models available. Some models have each half of the keyboard slightly bent from horizontal. This feature positions the keys to be in line with the arms and hands. Arms and hands at one s side are at an angle and not perpendicular to a keyboard. An ergonomic goal is to keep wrists straight, not bent. A slightly bent keyboard accommodates this natural position of a wrist. 

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