*4.4. Safety System Implementation*

As discussed in the methodology section, an array of ultrasonic sensors was needed to cover the all mobility range of the wheelchair. Two assumptions were made when choosing the number and positions of proximity sensors: the stopping distance is 1 m away from detected objects and that the electric wheelchair stops instantaneously. The electric wheelchair moves only forwards and rotates. Thus, the sensors were placed in front of the wheelchair to detect outward objects. An aluminum frame was built and mounted on the wheelchair to hold the sensors.

The three outward sensors, as shown in Figure 17, provided a horizontal detection range of 1 meter, with gaps of 8 centimeters between the covered regions ata1m distance from the aluminum frame. Moreover, the three sensors provided a 43 degrees detection angle. Two sensors were placed in between the three previous sensors, but slanted downwards. These sensors detected obstacles shorter than the aluminum frame.

**Figure 17.** Implemented proximity sensor design.

#### **5. Results and Discussion**

The complete system prototype is presented in Figure 17. This section provides the details of the metrics which can show the performance of real time wheel chair movement for disabled people using eye gazing.
