Bosch rexroth MCL, Project Planning Manual

Page: 136 / 206

9.20.6 Short-circuit of DC bus
Most of the power supply modules of Bosch Rexroth permit the DC bus to be
shortened when the power is switched off, which also establishes a short-cir‐
cuit between the motor phases. When the motor moves, this causes a brak‐
ing effect according to the principle of induction; thereby the motor phases
are short-circuited. However, the achievable braking force is not very high
and also depends on the velocity. The DC bus short-circuit can therefore only
be used to support existing mechanical braking devices.
9.21 Position and velocity resolution
9.21.1 Drive internal position resolution and position accuracy
In linear direct drives, a linear scale is used for measuring the position. The
linear scale for linear motors supply sinusoidal output signals. The length of
such a sine signal is known as the signal period. It is mainly specified in mm
or µm.
With the drive controllers from Bosch Rexroth, the sine signals are amplified
again in the drive (see Fig. 9-32 ). The drive-internal amplification also de‐
pends on the maximum travel area and the signal period of the length meas‐
uring system. It always employs 2 n grid points (e.g. 2048 or 4096).
f
int
Multiplication factor (S-0-0256, Multiplication 1)
s
p
Linear scale system signal period in mm (S-0-0116 Resolution
of encoder 1)
x
max
Maximum travel (S-0-0278, Maximum travel)
Fig. 9-31: Multiplication factor
Fig. 9-32: Drive-internal multiplication and/or interpolation of the measuring
system signals
With a known signal period and a drive-internal multiplication, the drive-inter‐
nal position resolution results as:
128/197
Application and construction instructions
MCL Ironless Linear Motors
Bosch Rexroth AG R911330592_Edition 06