HD65 & HD130 STEPPER DRIVES USER GUIDE 15

MS20 Microstep Card
Description The HD65M and HD130M drives are fitted with the MS20 Microstep
Card which gives improved resolution and smoothness from a
standard motor. Microstepping is achieved by proportioning the
currents in the two motor windings so that the rotor takes up a series
of intermediate step positions. In this way a standard 200-step
motor may be made to perform 1000 steps/rev (1/5 step mode), or
2000 steps/rev (1/10 step mode).
Ideally the intermediate current levels will produce equally-spaced
step positions as well as equal dynamic torque, without exceeding
the dissi-pation limit of the motor. In practice this can be difficult to
achieve and a compromise has to be made. If the current levels are
plotted against rotor position the resulting profile resembles a
sinusoidal shape. The optimum profile varies from one type of motor
to another, and for this reason the MS20 card has a selection of 64
alternative profiles which are stored in an Eprom and selected by an
8-position DIL switch. This switch is accessible between the two
edge connectors at the rear of the drive. The card has been
programmed with a set of profiles which have been derived
theoretically.
A sinusoidally-based profile is obtained with all bit switches in the
"off" position. Switches 2 - 6 may be used to set in an increasing
binary number which will cause the profile to progressively "fill out"
from a sinewave (switch 2 is the least significant bit). By turning on
switch 7, increasing the number in switches 2 - 6 will then trim the
profile down towards a triangular shape. In practice this tends to be
more useful than the "filled out" form. Switches 1 and 8 should be
left permanently off.
A few examples are shown below - a "1" indicates that the switch is
"on" .
Switch position Profile
8 7654321
0 0 0 0 0 0 0 0 Sinewave
0 0 0 0 0 0 1 0 Slight fill-out
0 0 1 0 0 0 0 0 Moderate fill-out
0 0 1 1 1 1 1 0 Maximum fill-out
0 1 0 0 0 0 1 0 Slight trimming
0 1 1 0 0 0 0 0 Moderate trimming
0 1 1 1 1 1 1 0 Maximum trimming

Setting Up the

Microstep

Card

Link 1 on the microstep card should be left in position "a". This link
is provided for future implementation of an alternative profile in
boost.