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Low Cost Automation Tutorial

#038 Motion Mechanism Design - 8 : Sensor Usages - 2

Category : Drive mechanism design
April16, 2010

There are various sensors used in LCA such as: micro switches that make physical contacts with work (MISUMI P/N MZW822, MZQ1, etc.); non contacting photo sensors (beam sensor: PEX11, photo-micro sensor: FPM24, etc.); and proximity sensor (PGXL8, etc.). Sensors must have environmentally extremely reliable outputs since the outputs determine the outcome of the control sequences to follow. Typical sensors and performances are introduced below. Select according to application specific needs.

(1) Characteristic comparisons of detection sensors

Switch typeMicro switch
Limit switch
Proximity sensorPhoto sensorPhoto sensor
Detection methodContactingNon-contactingNon-contactingNon-contacting
Detection principleMechanical switchMagnetic field detectionThrough beamReflective
Detection accuracy
Detection distance
Response time
Noise immunity
Environmental immunity (dust, water, etc.)

(2) Outline of various sensors

Contacting sensors (micro switches/limit switches) are disadvantaged in response time and operational life, but are often used where their superior noise immunity and actuation reliability are needed. Also, they are constructed to withstand many environmental adversities such as external forces, water, oil, dust, and wide temperature variations.
The proximity sensors that operate on magnetic field detection principle have sensing distance limitations. It is recommended to use within 70% of the maximum detection distance specification considering environmental temperature variations.

Photo sensors can be categorized into three groups based on the type of light receptor elements used.

Opposing through beam type
Reflex reflector through beam type
Two part construction with a reflector plate and a emitter/receptor element.
Reflective type
Single unit type containing emitter and receptor.

The through beam type is actuated when an object block the beam. The reflective type is actuated by a reflection from an object.