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
822
SPRUH22I – April 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
C28 Enhanced QEP (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 9-3. 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:
(1)
(2)
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.