Page 526 - Mechatronics with Experiments

JWST499-Cetinkunt
JWST499-c07
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P.S.
SW1
SW2
E.C.U Amp
Joystick sensor
Solenoid B
Cylinder
Solenoid B
Engine/electric
motor Pump Line relief
valve
E/M P

By pass
Proportional leakage
Cooler
valve orifice
Sensor
Filter Cross-over
Tank relief
valves
Line relief
valves
FIGURE 7.84: Control system components and circuit diagram for a single axis EH control
system which operates in two modes using closed loop control: (i) speed mode, (ii) force mode.

In addition, select an operator input device (joystick for motion command) with
the proper sensor, electronic control unit (ECU) with the necessary analog–digital signal
interfaces, position and force sensors on the cylinder for closed loop control (Figure 7.85).
The range and resolution requirements for the measured variables determine the
sensor and ECU interface requirements (DAC and ADC components). Let us assume that
the maximum speed will be mapped to a maximum analog sensor feedback signal (i.e.,
10 VDC), and the required accuracy is 0.01% of the maximum value which is 1 part in
10 000. In general, the measurement resolution should be at least 2 to 3 times better than
the required regulation (control) accuracy. Therefore, we need a speed sensor with a data
acquisition component that will have 1 part in 30 000 resolution. Let us assume that we
have selected a magnetostrictive position sensor (also called temposonic sensor) from which
speed information is digitally calculated. The output of the sensor can be scaled so that it
gives 10 VDC when the speed is at 2.0m∕s. The sensor nonlinearity should be better than
0.01% of the maximum range. In addition, the analog to digital converter (ADC) must be at
least 16-bit resolution in order to give a sampling resolution of better than 1∕30 000 parts
over the whole range (Figure 7.85).

Controller
P.S.
Pump/Tank
Sensor ADC/ CPU DAC/
PWM PWM
Valve
AMP
ADC/ (VtoI) solenoids Cylinder Load
PWM A & B

Sensor
FIGURE 7.85: Components and block diagram of a single axis electrohydraulic motion control
system. The controller is a programmable embedded computer.