Linear Encoder vs Rotary Encoder | difference between Linear Encoder and Rotary Encoder

This page compares Linear Encoder vs Rotary Encoder and mentions difference between Linear Encoder and Rotary Encoder.

Both of these encoders are used as position encoders.

What is a position encoder?
A highly accurate ruler or protractor which converts position into coded electrical signal is known as position encoder. They are available in wide range of sizes and specifications.

Encoders are used in wide range of industries electronics, aerospace, medical, scientific, motion control, semiconductor (for wafer handling robotics) , robotics, flat panel display, CMM, renewable energy, solar PV, print, metrology and so on. They are used in wire bonding, pick and place technology,

➤There are two types of encoders based on type of motion viz. linear and rotary.
➤Encoders can measure either incremental motion or absolute position.
➤Incremental encoder indicates relative motion where as absolute encoder indicates actual position.

Linear Encoder

• Linear encoder measures linear motion. The figure-1 depicts linear encoder from Renishaw plc.
• It measures the position directly on the axis slide. It is referred as closed loop.
• The spindle temperature has no effect as position is directly measured at the axis slide.
• Direct position measurement with linear encoders lead to precise machining results.

Rotary Encoder

• Rotary encoder measures rotary motion. The figure-2 depicts rotary encoder from Renishaw plc.
• It measures the rotary motion of the spindle.
• From the rotary motion and the screw pitch, the control calculates the position of the axis. It is referred as semi-closed loop. There is axis drift as spindle becomes warmer and expands slightly.
• In this type thermal expansion leads to position deviations.

Use of encoders in controlling moving axis of machines has following benefits or advantages.
➤It reduces manufacturing cost and time.
➤It reduces risk of axis losing control or crashing.
➤It provides instant position information on power up.

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