DESCRIPTION OF FORCE SENSOR & ULTRASONIC SENSOR

WEEK 17


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.