v(k)
[
X
t(k)
*
t(k
*
1)
+
X
D
T
v(k)
[
x(k)
*
x(k
*
1)
T
+
D
X
T
T
0
0.25T
0
±
0.1T
0
0.5T
0
±
0.1T
0
T
0
±
0.5T
0
QEPA
QEPB
QEPI
(gated to
A and B)
QEPI
(gated to A)
QEPI
(ungated)
Introduction
1959
SPNU563A – March 2018
Copyright © 2018, Texas Instruments Incorporated
Enhanced Quadrature Encoder Pulse (eQEP) Module
Quadrature encoders from different manufacturers come with two forms of index pulse (gated index pulse
or ungated index pulse) as shown in
. A nonstandard form of index pulse is ungated. In the
ungated configuration, the index edges are not necessarily coincident with A and B signals. The gated
index pulse is aligned to any of the four quadrature edges and width of the index pulse and can be equal
to a quarter, half, or full period of the quadrature signal.
Figure 34-3. Index Pulse Example
Some typical applications of shaft encoders include robotics and even computer input in the form of a
mouse. Inside your mouse you can see where the mouse ball spins a pair of axles (a left/right, and an
up/down axle). These axles are connected to optical shaft encoders that effectively tell the computer how
fast and in what direction the mouse is moving.
General Issues:
Estimating velocity from a digital position sensor is a cost-effective strategy in motor
control. Two different first order approximations for velocity may be written as:
(68)
(69)
where
v(k): Velocity at time instant k
x(k): Position at time instant k
x(k-1): Position at time instant k-1
T: Fixed unit time or inverse of velocity calculation rate
Δ
X: Incremental position movement in unit time
t(k): Time instant "k"
t(k-1): Time instant "k-1"
X: Fixed unit position
Δ
T: Incremental time elapsed for unit position movement.
is the conventional approach to velocity estimation and it requires a time base to provide unit
time event for velocity calculation. Unit time is basically the inverse of the velocity calculation rate.
