In the third week, i had research about the main sensor that i want to use such as ultrasonics sensorand also force sensor. The description of this sensor as below:
Ultrasonic sensors
Ultrasonic sensors work on a principle similar to radar or sonar which
evaluate attributes of a target by interpreting the echoes from radio or sound
waves respectively. Ultrasonic sensors generate high frequency sound waves and
evaluate the echo which is received back by the sensor. Sensors calculate the
time interval between sending the signal and receiving the echo to determine
the distance to an object.Maxsonar-EZ1 is operating at 5VDC voltage. It can
detect any object between 6 inches to 255 inches. The output of the sensor can
be serial, PWM or analogue. In this project analogue output is used, the
accuracy of the output is 10mV/inch. No
calibration required before using this sensor.
Force sensor / membrane potentiometer
Membrane potentiometers consist of thin layers, each with a specific
function, sealed inside a very thin protective envelope. Within the protective
envelope are the membranes; a resistive strip and a conductive strip. The
primary operational difference between a conventional potentiometer and a
membrane potentiometer is in the wiper mechanism.A conventional potentiometer
incorporates a resistive track and mechanical wiper. The wiper is spring loaded
and moves along the resistive track thereby providing for a variable
resistance. Tracks can be either linear or radial and various resistive
materials such as wire, conductive plastic, Cermet, etc. are used. Linear
motion potentiometers incorporate a wiper attached to a shaft that moves in
straight path. A rotary potentiometer has a wiper attached to a rotating shaft
which moves along the radial resistive track. Again, in a conventional
potentiometer, the wiper is in direct contact with the resistive material.
In a membrane potentiometer, the wiper does not make direct contact with
the resistive material but instead exerts a force through the top membrane
layer through to the conductive layer which in turn contacts the resistive
layer. This approach yields a much higher life cycle (in the millions) all
within an environmentally sealed package (IP65 or better).
Membrane potentiometers are also available in designs that totally
eliminate any mechanical contact between the wiper and resistive material
altogether. This is accomplished by using an external magnet and integrating a
metallic layer into the membrane potentiometer. The conductive layer of the
membrane potentiometer is pulled into contact with the resistive layer by the
magnetic force between the magnet and metallic layer. The result is the total
elimination of any actuating force on the potentiometer which yields 20+ million
life cycles .
Another design feature of a membrane potentiometer is its physical
package. The overall thickness of a typical membrane potentiometer is < 1
mm, well under the physical limitation of a conventional potentiometer which is
roughly 8 mm. A flat package also allows for a self-adhesive backing thereby
accommodating a wide variety of mounting options.
