**4.5 Autonomous elevation control**

The design incorporates intelligence in its elevating mechanism to detect when the user wants to stand. Strain gauge sensors are embedded on the lower back area of the wheelchair seat and when the user is seated, these sensors are in contact with the back area. They convert force, pressure, tension, weight, etc., into a change in electrical resistance which can then be measured. When external forces are applied to a stationary object, stress and strain are the result. The strain is defined as the displacement and deformation that occur. When the user needs to elevate to standing posture, they only need to bend their upper body, leaning forwards. This results in the displacement applied on the sensors (when greater than an average) and an electrical signal sent to the Arduino microcontroller which activates:

• The braking system of the wheelchair simply by covering the front ultrasonic sensor hence triggering the object avoidance system which cuts off power to

*Development of an Intelligent Standing Wheelchair with Reclining Characteristics DOI: http://dx.doi.org/10.5772/intechopen.96110*

the electric motors hence braking the wheelchair. Preventing the wheelchair from moving will aid to the stability of the user and reduce chances of falling over.

• The linear hydraulic actuators and hence the wheelchair lifts the user to a standing posture.

This is illustrated in the 5 steps shown in **Figure 8** below.

When the wheelchair reaches the maximum height, a signal is sent to the actuators to stop and remain bearing the weight of the user in standing posture. When the user needs to change from standing to seated posture, they can easily press the sit button on the joystick module. This reverses the direction of actuation of the lifting mechanism hence lowering the wheelchair back to its nominal position (**Figure 9**).

**Figure 10** shows the algorithm followed in elevating the user to standing posture.

### **4.6 Autonomous reclining control**

The design incorporates an autonomous intelligent reclining mechanism that is assisted by strain gauge sensors that are embedded on the top area of the wheelchair

**Figure 7.** *Decision making algorithm flow.*

**Figure 8.** *Screenshots of simulation steps taken in lifting the user.*

**Figure 9.** *Linear actuator lift and recliner concept in seated and standing posture.*

head rest. When the user needs to recline the seat, they lay their head on the head rest and apply a minimum force (greater than 45 N the force applied by the weight of an average head) on the headrest (assuming the user condition allows them to do move their head). When the minimum head force is received by the stress sensors and converted to electric impulses which are sent to the control unit. This will unlock the wheelchair back rest and allow it to move backwards slowly (as

*Development of an Intelligent Standing Wheelchair with Reclining Characteristics DOI: http://dx.doi.org/10.5772/intechopen.96110*

#### **Figure 10.**

*Algorithm followed to elevated posture.*

permitted by the actuators) until it reaches an angle of tilt desired by the user. When this angle is reached, the user stops applying the force on the headrest and this sends signals to the control unit, commanding the actuators to stop reclining the seat and lock the mechanism (as the actuators will bear the load applied). The range of the reclining angles of tilt is shown in **Figure 11** shown below.
