Page 521 - Mechatronics with Experiments

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ELECTROHYDRAULIC MOTION CONTROL SYSTEMS 507
valve can be controlled to achieve either flow or pressure regulation by simply selecting
a different software mode. The trend in valve technology is to implement the mechanical
control mechanisms by mechatronic control components, that is instead of using hydro-
mechanical control mechanisms, use electrical sensors, actuators, and embedded digital
controllers.

7.6 SIZING OF HYDRAULIC MOTION SYSTEM
COMPONENTS

Let us consider the component sizing problem for a one-axis hydraulic motion control
system shown in Figure 7.83. The question of component sizing is to determine the size
of the
1. pump(s),
2. valve(s) which includes main flow control valves, pilot valves, as well as safety
valves,
3. hydraulic motor(s) and/or cylinder(s),
4. the size of the hydraulic tank volume,
5. filtration circuit and filters,
6. hydraulic pipe diameters and their routing (minimizing bends and length),
7. hydraulic oil cooler if needed.
Over-sizing of components results in lower accuracy, lower bandwidth, and higher cost.
Under-sizing of components results in lower than required power capacity.
As a rule of thumb, a servo valve size should be selected such that the pressure drop
at the valve at maximum flow should be about 1∕3 of the supply pressure. In general, such

P = P - P -
v s T

Dm

T

FIGURE 7.83: Component sizing for a one-axis EH motion system: pump, valve, cylinder (or
rotary hydraulic motor) sizing for given load requirements.