*2.2.3. Display system*

The tasks depicted in Figure 3(c1) to (c4) were implemented in a program that used OpenGL graphical library to represent the virtual arm and prosthetic hand by the wire-frame drawing shown in Figure 3(d). The refresh rate was 25 frames/s, which was sufficient to give the impression of smooth motion. In addition, the GW displayed the processed EMG signals used as input. During the experiments, supplementary information was displayed to guide the subject to achieve the proposed goal.

maximum detected value). The EMG signals of each subject were normalized to the range of

Simulator of a Myoelectrically Controlled Prosthetic Hand with Graphical Display of Upper Limb and Hand Posture

To familiarize the subject with the equipment and functioning of the simulator, the subject was firstly instructed to freely move the virtual hand contracting his forearm muscles. When he felt comfortable with the system, the different sessions of experiments were performed. In order to avoid fatigue, a rest was scheduled between tasks, and the subject was not asked to keep any of the postures for more than a few seconds (Basmajian and Deluca, 1985; Kampas,

After the experiments, a short questionnaire was given to the amputee volunteer to gather feedback on the *Osaka Hand* and on its simulator. Some questions were based on the surveys described by Sears and Shaperman (1998) as well as Atkins *et al.* (1996). This gathered infor‐

Two types of experiments were carried out; the ones of the first block (3.1) were oriented to check whether the behavior of the simulator corresponded to the behavior of the *Osaka Hand*. The experiments of the second block (3.2) checked the controllability of the simulator.

EMG signals were acquired from one subject as explained in the previous section and given as input to the simulator and, simultaneously, to the *Osaka Hand*. In this way, we were able to compare their respective output, which is the angle of the fingers, when both were given the

Figure 5 shows the result of one of these experiments, carried out with a non-amputee subject freely moving the simulated hand. Figure 5(a) shows the inputs of the system: processed EMG signals of the wrist extensor muscle (dashed line) and those of the wrist flexor muscle (solid line). Figure 5(b) shows a comparison between the finger angle of the *Osaka Hand* (thick line) and the one given by the simulator (thin line). The average of the error (difference between the

(s.d. 0.39), with

http://dx.doi.org/10.5772/55503

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angle given by the simulated hand and that of the real *Osaka Hand*) was 0.85o

stiffness of the virtual hand fingers can be controlled in that same way.

, which we consider acceptable for our purpose.

As one of the main features of the *Osaka Hand* is that the subject can control its stiffness by antagonist muscles co-contraction, we performed another experiment to corroborate that the

To simulate different levels of co-contraction, we fed the simulator with different levels of *Ae* and *Af* under the condition (*Ae* = *Af* ) (see Figure 3(b) and (c1)). We sinusoidally modulated the

mation allowed us to plan the direction of our future research.

0-1 by their respective MVC values.

**3. Experiments and results**

**3.1. Behavior of the simulator system**

*3.1.1. Validation of the input-output relationship*

2001).

same input.

a maximum of 3.54o

*3.1.2. Variable stiffness*
