slides-04

(1)

DIGITAL ENCODERS AND

RESOLVERS

(2)

FALL 2002 MKM503E: Mechatronic System Components

2

Shaft Encoder Types:

• Incremental Encoders

• Absolute Encoders

Encoder Shaft Connection to power

supply and output terminals

(3)

Encoder Types:

• Incremental Encoders

As the transducer disk rotates, the encoder generates a train of pulses as a result of motion to be measured. By counting the pulses using the clock signal, both angular dislacement and velocity can be determined.

• Absolute Encoders

There are many pulse tracks on the transducer disk. As the absolute encoder disk rotates, several pulse trains equal in number to the tracks on the disk are generated

simultaneously. At an instant, the magnitude of each pulse signal level is a binary number. The pulses of tracks are organized so that each position of the shaft gives a coded digital signal.

(4)

4

Signal Generation Methods:

•Optical (photosensor)

•Sliding Contact

•Magnetic Reluctance

•Proximitty Effect

(5)

Optical Encoder

Magnetic Encoder

Sliding Contact Encoder

Proximity Probe Encoder

(6)

6

(7)

Internal Hardware of Incremental

Encoder

(8)

8

Shaped Pulse Signals

Clockwise Direction

Counterclockwise Direction

(9)

Quadrature Signal Addition to Improve Physical Resolution

(10)

10

Data Acquisition System for

Incremental Encoders

(11)

1 max min

2

−

θ

=

θ

r

1

2 resolution

digital

1 min max

−

θ

−

θ

=

₋ r

1

2

1

−

=

r−

M

maximum

possible counts data size in _bits

max

θ

=

θ

M

n

range of encoder angular dislacement

DISPLACEMENT COMPUTATION

(12)

12

Methods for determining angular velocity

• Pulse Counting Method

There is a lower speed limit. Not very accurate at low speeds!

• Pulse Timing Method

The time for one encoder cycle is measured using high-frequency clock signal. Accurate at low speeds.

VELOCITY COMPUTATION

NT

n

π

=

ω

2

number of windows sampling period number of pulses counted

PULSE COUNTING METHOD PULSE TIMING METHOD

Nm

f

π

=

ω

2

number of windows cycles of the clock signal clock frequency

(13)

PHYSICAL RESOLUTION

DISPLACEMENT RESOLUTION

one-pulse signal

N

p o

360 =

θ

∆

N

p

4

360

o

=

θ

∆

quadrature signal DIGITAL RESOLUTION r d

2

360

o

=

θ

∆

(14)

14

Absolute Encoder Disk Patterns

Gray Code Binary Code 1 bit switching 4 bits switching

(15)

Digital Resolver

Pulse Tachometer Hall Effect Shaft Encoder

Hall Effect Sensor