WYFFOS - SLIT TRANSLATION DC MOTOR DRIVER

SLIT TRANSLATION DC MOTOR DRIVER

Contents:

1. Introduction:

This motor drive card has been specifically designed to power the WYFFOS slit translation dc motor. Being a simple mechanism to operate the requirements for this mechanism are met in hardware for velocity, but software for translation distance, direction and enable.

1.1 Document history:

1.2 Version notes:

1.3 Mnemonics used throughout the text:

2. Circuit card:

The circuit card is the standard 3U x 160 eurocard with a DIN 41612 edge connector and is mounted vertically in the WYFFOS LIMPIT sub-rack. A free flow of air around the card is required, forced cooling is unnecessary.

3. Circuit description:

The circuit drives a dc motor from an enable, step-pulse and set-direction inputs. This simple design saves the cost of an expensive VME dc motor controller when operating a mechanism such as the slit translation dc motor-mike. The circuitry cannot determine step-pulse frequency to alter motor velocity, so the set-speed potentiometer on the card must be calibrated against the EPICS record for this mechanism in steps per millimetre travelled. This is especially important for any mechanism that is absolute encoded such as the slit translation drive. Accurate speed calibration will minimise the number of attempts the software takes to reach final position.

The actual motor driver is a four quadrant, linear output motor driver from RS (stock no. 715 005) which employs an armature feedback technique to maintain speed regulation. For the slit translation drive the motor load varies depending on direction, so this feedback technique aides setting accuracy and minimises under or overshoot of the demanded position.

The remaining circuitry consists of opto inputs as a standard interface to a VME driver output and a Exclusive OR gate (SN7486) providing signal sense selection. A retriggerable monostable (SN74LS122) configured to trigger on the Schmitt B1 input leading edge ­and with a time-out period calculated slightly longer than the input frequency of 1Khz. The Q output remains hi only whilst step pulses are on the input. Time out period £1.2ms. The Q output is connected to a dual peripheral driver Ic.(SN75452) 1A input, whose 2Y output drives a relay switch to turn on the driver module. The other input gate is used to set the direction polarity relay determined by the logic level on input 2A Inputs 1B/2B are linked and provide an enable gate to the driver module signals. The driver module powers the motor for the duration of step pulses, in the set direction and at the preset speed when enabled.

4. Circuit diagram:

5. Parts lists:

Component                 Manufacturer & part   Supplier & order   No.    Cost per
                                 number               code         off      item

100 x 160 circuit board        Bicc Vero          Electrospeed      1      £8.49
                               03-0026J             03-0026J

Connector class 2               Harting           Electrospeed      1      £4.28
W/wrap 64/96                 0903.164.6928          17-1222E

Retriggerable monostable       National                RS           1      £0.75
multivibrator  IC.             74LS122               639-305

Peripheral driver IC.      Texas Instruments           RS           1      £0.61
                               SN75452               649-302

Optocoupler IC.                 Sharp                  RS           1      £1.59
                                PC847                175-132

2 input XOR gate IC.          Motorola                 RS           1      £1.66
                             SN74LS86N               644-234

Rp1. 470R SIL package          Bourns                Farnell        1      £0.42
                            4308R-102-470R           106-179

Rp2. 4K7 SIL package           Bourns                Farnell
                            4309R-101-4K7            106-192



1
£00.431

Subminiature SPCO 5V
relay

RS
348-526
2
£01.41

Servo motor drive module
and data sheet

RS
715-005
1
£80.79

Multiturn cermet trimmer
linear 10KW

RS
160-225
1
£01.02

4K7W 0.25W M.F resistor

RS
148-663
2
SSM=10
£0.032

1KW 0.25W M.F resistor

RS
148-506
1
SSM=10
£0.032

80K6W 0.125W precision
M.F 0.1% resistor
E96 range
RS
167-591
1
SSM=5
£00.77

1N4001 1A diode
General Instrument
RS
261-148
2
SSM=10
£00.048

0.1µf decoupling capacitor
ceramic


3
from
stock

33,000pf  precision ±1%
radial lead capacitor
Philips components
RS
115-354
1
SSM=5
£00.82













3
H.M.Stevenson  Manual.doc



5
H.M.Stevenson  RGO/C  WYFFOS motr_drv.doc





6
H.M.Stevenson RGO/C WYFFOS motr_drv.doc