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SENSORS (Future Trends and Factors
Affecting Sensors and Automation
in…
SENSORS
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CHARACTERISTICS
Size and Weight
Depending on application of the sensor, the size may be of primary importance for example joint replacement sensors have to be adopted into the design of joints and move with the robot body element. The weight of sensor is also very important. A heavy sensors adds to the inertia of the arm and reduces its overall payload.
Type of Output
The output of the sensor may be digital or analog.
Depending on the application this may be used directly
or to be converted. The output of potentiometer is analog whereas that of an encoder is digital.
Interfacing
Sensors must be interfaced with other devices such as microprocessors and controllers. The interfacing between the sensor and the device can become an important issue if they do not match or if other add on components and circuits become necessary.
Resolution
Resolution is the minimum step size within the range of measurement of the sensor. In wire wound potentiometer it will be equal to the resistance of one turn of the wire. In digital device it is equal to (Full range/(2n))
Sensitivity and Linearity
Sensitivity is the ratio of change in output in response to a change in input and linearity represents the relationship between input variations and output variations. Highly sensitive sensors will show large fluctuations of output as a result of fluctuation in input.
Response Time
Response time is the time that a sensor’s output requires to reach a percentage of total change. It is usually expressed in percentage of total change such as 95%.
Reliability and Accuracy
Reliability is the ratio of how many times a system
operates properly divided by how many times it is used.
While accuracy is defined how close the output of the
sensor is to the expected value
TYPE OF
SENSORS
2. Position Sensors
Used to measure displacements,
both angular and linear as well
as movements
Types
Potentiometer
Converts position information into
a variable voltage through a resistor.
As the sliding contact slides on the resistor
due to change in position the proportion of
the resistance varies
Linear Velocity Differential Transducer (LVDT)
It is actually a transformer whose core moves with the distance measured and that outputs a variable analog voltage as a result of his displacement
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3. Visible Light and Infrared Sensors
React to the intensity of light projected onto them by
changing their electrical resistance. If intensity of light is zero,
the resistance is at maximum. As the light intensity increases
the resistance decreases and consequently current increases.
These sensors are very useful and can be used in making
optical encoders.
4. Torque Sensors
Torque can be measured by pair of strategically placed forced sensors. Suppose the two sensors are placed on shaft, opposite to each other, on opposite sides. If a torque is applied to the shaft, it generates two opposite forces on the shaft body, causing strains in opposite direction. The two sensors an measure the forces that can be converted into the couple.
Definition
a device that detects and responds to some type of input from the physical environment. The specific input could be light, heat, motion, moisture, pressure, or any one of a great number of other environmental phenomena. The output is generally a signal that is converted to human-readable display at the sensor location or transmitted electronically over a network for reading or further processing.
In robotics, sensors are used for both
internal feedback control and external
interaction with the outside environment
There are huge array of sensors available for measuring
almost every phenomenon. We will limit our discussion to
sensors used in conjunction with robotics, automation and
manufacturing industry.