Chapter 14 - LIDA Encoder Information

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ERA 780 (Chara) Angle Encoders

User's Manual

Contents

1.- Description of the Angle Encoders

1.1.- Description of Scale

1.2.- Description of Scanning Head

2.- Mounting the Angle encoder

2.1.- Mounting of the Scale Tape

2.2.- Mounting the Scanning Heads

3.- Components of each Angle Encoder

4.- Specifications

4.1.- General Information

4.2.- Electric Data

4.3.- Mechanical Data


1.- Description of the Angle Encoders

An angle encoder consists of

- 1 scale

- 1 scanning head with cable 3 m in length

1.1.- Description of scale

The measuring standard in the exposed angle encoder is a single AURODUR steel scale tape whose length is exactly matched to the inside diameter of the cylindrical bearing surface.

Scale tape slot floor diameter: 1123,95 mm
Tape cross section: 13.2 mm x 0.3 mm
Tape material: Stainless steel
Grating period: 40 um
Number of grating periods: 88260
Reference marks: Distance coded, one reference mark track parallel to the incremental track.

The unique method of mounting the scale tape allows a measuring of 360º. Pressing the scale tape into its slot until it snaps into place ensures that the tape retains itself in the slot. The measuring error at the tape butt joint in the area of the tensioning cleat therefore remains far below the values that would result if it where necessary to use fasteners. The scale is glued in the scale carrier in order to prevent it from slipping.

1.2 Description of Scanning Head

The Angle Encoder functions according to the reflected-light principle. As the scale rotates the periodic light fluctuation in the scanning head is transformed into electrical signals by photovoltaic cells. The two sinusoidal signals produced in this way from the incremental track are shifted with respect to each other by one fourth of a signal period. The reference signal is a signal peak that crosses zero at half amplitude, at which level it has a width of approx one signal period of the incremental signal.

2.- Mounting the Angle Encoders

2.1.- Mounting the Scale Tape.

First, the scale tape slot must be centrered and aligned.

Clean the scale tape slot with alcohol (or acetone) using a soft, lint-free cloth.

Spread a thin coat of adhesive in the scale tape slot and then level it with a suitable tool (e.g. a razor blade) to produce a thin and even coating approex 0.01 mm thick. The area near the tape butt joint (approx +/- 2 mm) should be free of adhesive so that none can come between the ends of the tape.

Recommended adhesive:

UHU plus endfest 300, a two component epoxy resin adhesive, article number 45640, made by UHU GmbH in 77813 Buhl (Baden), Germany.

Lay the scale tape, which has been cleaned by HEIDENHAIN, in the prepared slot. Make sure that the position of the reference mark relative to the scanning head. Using your hands, lay the two ends of the tape together and, starting from the butt join, press the tape into the slot as far as it will go. A wave in the tape should result which should be located at 180º from the butt joint. Now press the wave into the slot until the tape snaps into place.

Press the tape along its entire circumference against the edge of the slot, which was manufactured with an axial runout of 0.2 mm. Remove any adhesive residue and clean the tape . The working time of the adhesive is aprox 2 hours at 20ºC (68ºF). The hardening time of the adhesive is approx 12 hours at 20º C. Ensure particularly that the scale tape ends lay exactly flat on the curvature of the slot floor during the hardening process.

2.2.- Mounting the Scanning Heads

Remove the reticle shipping protection.

Clean the reticle with alcohol or acetone using a lint-free cloth.

Clean the mounting surfaces

To fasten the scanning head you will need:

 

- 1 mounting bracket

- 2 cap screw (M4 x 10 as per ISO 4762)

- 2 cap screw (M4 x 6 as per ISO 4762)

- 4 washers (4.3 as per DIN 433)

- 0.5 mm and 0.2 mm spacer foil.

Align the mounting bracket and tigthen it loosely with the two M4 x 10 screw and washers. Before setting the scanning gap, find a position on the circunference of the scale that lies at the mean value of radial motion.

To set the scanning gap, lay the spacer foil between the scale and the mounting bracket, and lightly press the mounting bracket against the spacer foil and its bearings surface. Both edges of the mounting bracket must lie evenly against the spacer foil.

Tighten the mounting bracket with both M4 x 10 screws. Then gently pull the spacer foil out in a tangential direction.

The scanning head is then screwed loosely onto the mounting bracket with the two M4 x 6 screws and washers and at the same time aligned parallel to the mounting surface. From this settingthe amplitudes of the 0º and 90º incremental signals are set and the exact reference mark position is defined by moving the scanning head relatively to the scale. It is necessary here that the scanning head be rotated in the mounting bracket.

For the best possible adjustment, we recommend the HEIDENHAIN Encoder Diagnostic Kit with the PWM 7 Phase Angle Measuring Unit. Also, an oscilloscope is needed for X-Y operation. Connect the output socket of the PWM 7 with an oscilloscope. Set the sensitivity of the oscilloscope to 0.5 V/cm or 1 V/cm and DC.

Set selector switch 2 of the PWM 7 to position (reference mark signal). The trigger point of the oscillograph must be set to the negative edge of the reference mark signal. Now move the reference marks past the scanning head several times unad, using a size 7 screw driver, turn the threaded sleeve until the peak of the reference pulse settles at the peak.

When the setting is correct, screw the scanning head firmly into position. Repeat this procedure for the second scanning head.

3.- Components of each Angle Encoder

 

1. 1 scale tape

2. 1 scanning head with cable length 3 m

3. 1 mounting bracket

4.0.5 mm and 0.2 mm spacer foil

5. User Manual

4.- Specifications

4.1 General Information

Incremental angle encoder system with the following features:

- 5 V power supply

- LED illumination

- Symetrical 11 uA current interface (incremental signals)

- Rated frequency range 0 to 200 Khz.

- Incremental, sinusoidal output signals

4.2 Electrical Data

The encoder supplies signals to the "incremental analog output" interface 011 AE 262 714 00

Additional Data and Deviations

4.2.1 Scanning Illumination

One light unit, consisting of an LED and condenser lens, drives all sensors.

Note: The use of only one light unit for all sensors ensures minimum signal drift.

4.2.2 Electronics

- Functional groups: Silicon planar photovoltaic cells

4.2.3.1 Cable Mounted on Scanning Head

- Cable Length:

3 m

- Designation: Polyurethane cable PUR sw 4.5 x 2 x 0.05 + 1 x 0.05 (double shielding)
- Type of connection:

- in the encoder: leads are soldered on directly
- at the output: connector

- Assignment: See Drawing 011 AE 280 772 00 (Electronic Laboratory)

4.2.3.2 Connecting Cable

- ID number: 262 004

4.2.4 Output Signals

The encoder supplies three differential signals

I1 = 0º

I = 90º

I = RP

Positive direction: The positive counting direction is clockwise. seen from the mounting surface side of the scanning head housing (see dimensional drawing)
Equivalent circuit: Approx. <2nF without cable

Signal values

Only deviations to 010 AE 261 114 00 are indicated

Up = 5V

f = 1Khz

Measurement at scanning head output.

Signal Values
Minnimum
Maximum
Phase |D1 + D2|:2
85º
95º
90º +/-5º
Phase Angle at Scale butt Joint
80º
100º
90 +/-10º

- Recommended receiver circuit and shielding concept

Permissible reference voltage of the receiver circuitry: Uo1 = 0V to + 7.5 V

4.3 Mechanical Data

4.3.1.- These data apply for the scale holder at the inside diamenter of the scale carrier. The scale is fastened in a corresponding slot and without tensioning cleat. The entire diameter is covered with one scale (1 butt joint/360º)

4.3.1.1

Line counts (N)

The line counts depend on the Scale Tape Mount Diameter (Dia. D), since the grating period of the AURODUR steel scale is always 40 µm.

Int (integer): whole number part of the expression in brackets.

4.3.1.2 Scale Tape Mount Diameter (Internal)

4.3.2.- Mechanical Data

Scale: AURODUR Grating on Steel Strip
Coefficient of expansion of the AURODUR scale tape: 10.5 ppm/K
Grating Period: 40µm

Maximum Scanning Frequency:

200 Khz
Reference Marks: Distance Coded, Next to the Incremental track
Type of Protection:

Scanning Head: IP 54 (IEC 529)
Scale: Unprotected

Corrosion Protection: Scanning Head: Anodized Aluminium
Scale: Stainless Steel
Measuring Range: 360º (1 butt)
Operating Temperature Range: -10ºC to +50ºC
Storage Temperature Range: -20ºC to +70ºC
Relative Humidity: 85% (condensation not permitted)
Mass: Scanning Head: Approx. 0.23 Kg (12.346 oz)
With cable and connector.

Mounting Images

 

 

 

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