Page 531 - Mechatronics with Experiments

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JWST499-Cetinkunt
JWST499-c07
ELECTROHYDRAULIC MOTION CONTROL SYSTEMS 517
X ,V d
d
PID
position
ENC
Scale
DAC
F
d
PID
P 1 force
A 1
P 2
A 2
X min X max
F Mode selector
PRX 1 min
PRX 2 logic
FIGURE 7.88: Real-time control algorithm for the EH control system using both position and
force feedback and implement a “bumpless mode transfer.”

ON/OFF sensor (i.e., proximity or photoelectric sensor) can be used to establish the absolute
reference.
Once the starting position is accurately established after power-up (home motion
sequence is completed), the system is to operate in position servo mode, followed by a
force servo mode and then followed by position servo mode again to return to the starting
position. Therefore, all that is needed is the logic to decide when to switch between the two
modes (Figure 7.88).
Let us assume that we have the parameters for motion, and the I/O registers mapped
to variables as follows,

Given: Programmable motion parameters
v d−fwd desired forward motion speed
a desired forward motion acceleration
d−fwd
v desired reverse motion speed
d−rev
a desired reverse motion acceleration
d−rev
x minimum value of cylinder position where pressure is expected to rise
min
x maximum value of cylinder position where pressure is expected to rise
max
t time period for which to apply pressure.
press
I/O signal registers:
Enc accumulated encoder counts since the end of home cycle
P pressure sensor signal 1
1
P pressure sensor signal 2
2
Prx ON/OFF sensor used to establish home reference
1
Prx ON/OFF sensor used to establish end of force cycle
2
DAC digital to analog converter register.