by measuring the frequency of either the QEPA or QEPB output, the processor can determine the velocity of the
motor.
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.
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)
Figure 7-3. Index Pulse Example
Some typical applications of shaft encoders include robotics and 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:
v(k)
[
x(k)
*
x(k
*
1)
T
+
D
X
T
(1)
v(k)
[
X
t(k)
*
t(k
*
1)
+
X
D
T
(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
• ΔX = Incremental position movement in unit time
• t(k) = Time instant "k"
• t(k-1) = Time instant "k-1"
• X = Fixed unit position
• ΔT = Incremental time elapsed for unit position movement
event for velocity calculation. Unit time is basically the inverse of the velocity calculation rate.
Enhanced Quadrature Encoder Pulse (eQEP)
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
TMS320x2806x Microcontrollers
463
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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