Chapter 8. Digital and Analog Interfacing Methods

Transcription

1 Chapter 8 Digital and Analog Interfacing Methods

2 Lesson 11 Optical Rotatory Incremental Encoder

3 Outline Incremental Rotatory Encoder Disc, tracks and index hole Encoder Interface Circuit Pulses from a rotating encoded disc on a shaft

4 Incremental Rotatory Encoder System, which notes the increments or decrements at each step change in the angle when a shaft rotates by one step-angle, clockwise or anticlockwise, respectively.

5 Parts of an Incremental Rotatory Encoder Circular disc- two tracks with equally spaced slots and index-hole Disc index-hole marks the 0 w.r.t. an assumed axis around which the disc rotates

6 Parts of an Incremental Rotatory Encoder Three LED-phototransistor pairs, one pair is for the hole and two are for the two tracks a and c slots Tracks a and c slots have slight offset (angular displacement) to enable noting the increments by one and the direction of motion by phase detection

7 Parts of an Incremental Rotatory Encoder Each track on the disc has the slots at successive steps on the circumference over angle 0- to 360- A track, a or c counter notes the movements stepwise. Counter a or c counts the movements stepwise.

8 Outline Incremental Rotatory Encoder Disc, tracks and index hole Encoder Interface Circuit Pulses from a rotating encoded disc on a shaft

9 track c 64 slots in 6-bit output encoder Index hole track a 64 slots in 6-bit output encoder Incremental Rotatory Encoder Disc

10 n-bit incremental rotatory encoder 1. Counts the clockwise and anticlockwise angular rotational steps 2. When the shaft rotates clockwise or anticlockwise, the numbers of occurrences of either 1 s (or 0 s) are counted. Counting is upwards for clockwise rotation and downward for

11 n-bit incremental rotatory encoder 3. Resolution is (360 /n) when there are n slots 4. For a resolution of (360 /64), each track has 64 arcs, which are dark and 64 slots or transparent areas. Six bit counter can be external or internal timer-counter in MCU

12 n-bit incremental rotatory encoder 5. Counts reset to 0 on active input when index-hole passes trough the LED radiation

13 Outline Incremental Rotatory Encoder Disc, tracks and index hole Encoder Interface Circuit Pulses from a rotating encoded disc on a shaft

14 Incremental Rotatory Encoder LED-PT Pairs R +5V hole Rc GND GND +5V Port bit

15 Incremental Rotatory Encoder LED-PT Pairs +5V R Rc track a Rc GND GND GND +5V track c Port bit Phase detector

16 Incremental Rotatory Encoder LED-PT Pairs R +5V track a Rc Counts counts up or down as per phase detector input GND GND +5V Counter Port bits Phase detector

17 Outline Incremental Rotatory Encoder Disc, tracks and index hole Encoder Interface Circuit Pulses from a rotating encoded disc on a shaft

18 Pulses for Inputs from a and c and hole track a slots track c = slots Phase difference Pulses of index hole on each full rotation

19 Summary

20 Incremental rotatory encoder Enables the measurement of a shaft angular position at an instant with respect to an origin (at a fixed initial angular position). Enables measurement of the rotational speeds also from number of input pulses per second.

21 End of Lesson 11 Optical Rotatory Incremental Encoder

22 THANK YOU