HEDS-9200360 查看數據表（PDF） - HP => Agilent Technologies

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HEDS-9200360

Two Channel High Resolution Optical Incremental Encoder Modules

HP => Agilent Technologies 

Block Diagram

2

Output Waveforms

Theory of Operation

The diagram shown on the fol-

lowing page is a block diagram of

the encoder module. As seen in

this block diagram, the module

contains a single LED as its light

source. The light is collimated

into a parallel beam by means of a

single polycarbonate lens located

directly over the LED. Opposite

the emitter is the integrated

detector circuit. This IC consists

of multiple sets of photodetectors

and the signal processing

circuitry necessary to produce the

digital waveforms.

The codewheel/codestrip passes

between the emitter and detector,

causing the light beam to be

interrupted by the pattern of

spaces and bars on the code-

wheel. The photodiodes which

detect these interruptions are

arranged in a pattern that

corresponds to the codewheel/

codestrip. These detectors are

also spaced such that a light

period on one pair of detectors

corresponds to a dark period on

the adjacent pair of detectors. The

photodiode outputs are then fed

through the signal processing

circuitry resulting in A, A, B, and

B. Comparators receive these

signals and produce the final

outputs for channels A and B. Due

to this integrated phasing

technique, the digital output of

channel A is in quadrature with

that of channel B (90 degrees out

of phase).

Definitions

Count (N): The number of bar

and window pairs or counts per

revolution (CPR) of the

codewheel.

1 cycle (C): 360 electrical degrees

(°e), 1 bar and window pair.

1 Shaft Rotation: 360 mechanical

degrees, N cycles.

Pulse Width (P): The number of

electrical degrees that an output

is high during 1 cycle. This value

is nominally 180°e or 1/2 cycle.

Pulse Width Error (∆P): The

deviation, in electrical degrees of

the pulse width from its ideal

value of 180°e.

State Width (S): The number of

electrical degrees between a

transition in the output of channel

A and the neighboring transition

in the output of channel B. There

are 4 states per cycle, each

nominally 90°e.

State Width Error (∆S): The

deviation, in electrical degrees, of

each state width from its ideal

value of 90°e.

Phase (φ): The number of elec-

trical degrees between the center

of the high state of channel A and

the center of the high state of

channel B. This value is nominally

90°e for quadrature output.

Phase Error (∆φ): The deviation

of the phase from its ideal value

of 90°e.

Direction of Rotation: When the

codewheel rotates in the direction

of the arrow on top of the

module, channel A will lead

channel B. If the codewheel

rotates in the opposite direction,

channel B will lead channel A.

Optical Radius (Rop): The dis-

tance from the codewheel’s center

of rotation to the optical center

(O.C.) of the encoder module.

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