Sensor - Research Paper Example

The feedback system is designed so well that it updates the status of input torque in fraction of a second and as a result exoskeleton keeps working accordingly; and works well with frequent torque changes. A heel pressure sensor is required that produces an electrical signal whenever heel touches the ground or force is sensed on the heels because of its interaction with the ground. Signal from this sensor helps in regulating the sequential movement of the exoskeleton. These force sensors are usually generated by making use of a couple of force sensors but in our design use of a simple piezoelectric or capacitive device works well as a heel sensor and is placed on the heel of the exoskeleton design on the side that is directly in touch with the ground.

In order to accurately track the force applied by the user to the legs on the exoskeleton distributed force sensors will be used. These sensors help in measuring distributed forces being applied by the human body over a specified area rather than collective force applied to the entire leg. This approach of distributed force helps to track the applied force at any given point on the leg during the gait to check for proper rehabilitation of the leg. Sensors placed under each heel will sense whether the foot is in contact with the ground, signaling to the leg that the motion should come back to a standing phase.

Myographic Sensors Electro-Myographic sensors are used to directly measure the electrical activity of human muscles. In case of exoskeleton, myographic sensors can be placed on the belly of muscle. In this case, electrical activity of human muscles is directly translated to force that is being exerted by the leg onto the exoskeleton, by measuring the amplitude of the force. There is a limitation in using EMG technique in the design of lower limb exoskeleton. If EMG is incorporated in the design of exoskeleton then wearing this device would not remain convenient for the patients as electro-myographic sensors need direct interface to the skin.

This can be avoided by making use of acoustic myographic techniques. In short these sensors are used to keep record of the current muscular activity of the lower limb and helps in detecting whether or not the lower limb is capable of recovering to its original state. Other than that these sensors can also be incorporated to replace strain gauges that are being used in our design to measure the force being applied by the leg on the exoskeleton. This can be done by simply applying acoustic sensors between the knee and ankle of the human leg and the resulting signals can be transformed into energy magnitude.

From this force being exerted on the lower limb can be determined easily. Acoustic sensors are not able to provide direct signal to the control system as the signal is too low when observed in terms of voltage. Therefore, we need pre-processing circuitry to reduce hardware induced noise as well as improve signal quality. BU-7135 is an accelerometer based acoustic myographic sensor. It is covered with a silicon case and accelerometer is placed within this cover. It is then protected by a layer of PCB and air chamber is also provided before having contact either the skin through silicone membrane.

Here is the detailed diagram showing the internal structure of the device. The AMG sensor is not used individually within the circuit, rather pre-amplification circuit is provided along the sensor to get better signal. Here is the design of