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FEEDBACK DEVICES

FEEDBACK DEVICES. FEEDBACK DEVICES. Feedback is required in closed loop system These devices provide position and velocity signals Generally these are rotary devices Devices are – Rotary encoders – Incremental & Absolute Linear encoders Resolver Tachometers. Incremental Rotary Encoder.

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FEEDBACK DEVICES

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  1. FEEDBACK DEVICES

  2. FEEDBACK DEVICES • Feedback is required in closed loop system • These devices provide position and velocity signals • Generally these are rotary devices • Devices are – • Rotary encoders – Incremental & Absolute • Linear encoders • Resolver • Tachometers

  3. Incremental Rotary Encoder • Most common in robots & NC systems • Shaft driven device produces electrical pulses as output • Pulse frequency α shaft speed • Contains glass disk marked with clear & opaque segments alternately on periphery • This disk is connected to the lead screw • Light source is placed one side of disk & a photocell on another side • As disk rotates, light falls periodically on photocell which produces sinusoidal output signal in mV.

  4. Incremental Rotary Encoder • Output signal is amplified and converted in square-wave signal by Schmitt – trigger circuit • A rotary encoder with 360 lines can give 360 pulses per revolution and if a lead screw with 3.6 mm pitch is connected to such an encoder, it will give one pulse for every 0.01 mm linear movement of slide.

  5. Linear Encoders • Instead of disc, glass scales with line grating are used • This glass scale is connected to slides so have sliding motion • Relative movement b/w glass scale & photocell results in alternate light pulses which generates electric pulse same way as in rotary encoder

  6. Absolute Rotary Encoder • Uses a multiple – track disk using binary or grey code concept • It gives more accurate shaft position • Working is same as incremental rotary encoder

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