Emerson EZMotion User Manual page 93

= 2279 - 1375 + 0
= 904 revs
Note that this value is NOT correct. This is because after 5000 revs, we have exceeded the absolute resolution of the encoder
in a single direction.
So you can see that when using One-Sided Mode, as long as the motor does not move more than 4096 revolutions in the
positive direction from the home position, EZMotion can correctly calculate the absolute machine position on power up.
Two-Sided Mode
Two-Sided Mode implies that once the absolute home position has been defined, the user wishes to distribute the full multi-
turn resolution of the encoder evenly in BOTH DIRECTIONS from the home point. Using the example of a 12-bit multi-turn
absolute encoder, the motor could then travel 2048 revs in either the positive or negative direction without experiencing any
problems due to absolute rollover. IMPORTANT NOTE: In Two-Sided mode, if the motor moves in excess of 2048 revs in
either direction from the home position, EZMotion cannot detect this condition, and therefore the absolute position would be
incorrectly calculated on the next power up.
Example:
The user homes the motor to a sensor. When the sensor activates, the motor is at the machine home position P
(where P is the Position feedback of the Machine). When the motor is at the home position of 0 revs, the absolute encoder
M
reads P = 1375 revs (where P
A
chosen number for demonstration purposes. Therefore, EZMotion now uses this relationship of P
position to calculate the machine position (P
Position Feedback of Machine when at Home = P
Position Feedback of Absolute Encoder when at Home = P
We then need to calculate the value equal to half the resolution of the encoder (E
encoder resolution in half. This is the position feedback of the absolute encoder at the rollover point (or P
E = Max Resolution / 2
half
= 4096 / 2
= 2048
P = P + E
AR AH half
= 1375 + 2048
= 3423
P must be within the max resolution of the encoder, so if P
AR
subtract the max resolution:
P = P - Max Resolution
AR AR
If the motor then moves 1000 revs in the positive direction, P
2375. If the machine is powered-down and then back up, EZMotion would read the position from the absolute encoder P
subtract the position of the absolute encoder at the home position P
the home position P
MH
Calculation #1: Used when P
P = P - P + P
M A AH
= 2375 - 1375 + 0
= 1000 revs
If the motor is again at the home position and then moves 1000 revs in the negative direction, P
-1000. If we power down, and then back up, P
are met, so we will use it again to find P
P = P - P + P
M A AH
= 375 - 1375 + 0
= -1000 revs
If we now start from the home position again, and move the motor 2000 revs in the negative direction, P
or P = -2000. If we power down and then back up, P
M
is a 12-bit multi-turn absolute encoder, when traveling in the negative direction, the absolute encoder rev counter will reach 0
and rollover to 4096. Therefore, we will never get a value of -625 on the absolute encoder. In this case, the absolute encoder
would read P = (P
A AH
Two-Sided Mode, EZMotion can interpret this position from the absolute encoder to calculate the correct machine position. If
the machine was powered-down, and then back up, the P
Calculation #2: Used when P
P = P - P - Max Enc Resolution + P
M A AH
EZMotion User/Programming Guide
Revision A8
is the Position feedback of the Absolute Encoder). In this example, 1375 is just a randomly
A
) on power up.
M
MH
, to get P .
M
> E AND P < P
AR half A AR
MH
would be P
A
.
M
MH
- 2000) + Max Encoder Resolution = 3471. Since the user has defined the application type to utilize
> E AND P > P
AR half A AR
MH
www.controltechniques.com
= 0
= 1375
AH
half
calculated above is > Max Encoder Resolution we need to
AR
will be P + 1000 or P
M MH
, and then add the position feedback of the machine at
AH
- 1000 or P = 375. Once again, the conditions for Calculation #1
AH A
should be P - 2000, or P
A AH A
would be calculated as follows:
M
= 0 revs
M
and P at the home
M A
), and the position that distributes the
).
AR
= 1000,and P is P + 1000 or P
M A AH
will be P - 1000 or P
M MH
will be P
M
= -625. However, we know that since this
=
A
,
A
=
M
- 2000
MH
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