Actuator for two-position valves
The 2-Position Valve Actuator block represents an actuator that you can use with directional valves to control their position. This actuator can drive a two-position valve. The block is developed as a data-sheet-based model and all its parameters are generally provided in catalogs or data sheets. The key parameters are the stroke, switch-on, and switch-off times.
The block accepts a physical input signal and produces a physical output signal that can be associated with a mechanical translational or rotational push-pin motion. Connect the block output to the directional valve control port.
The actuator is represented as an ideal transducer, where output does not depend on the load exerted on the push-pin and the push-pin motion profile remains the same under any loading conditions. The motion profile represents a typical transition curve for electromagnetic actuators and is shown in the following figure:
The push-pin is actuated when the input signal value crosses the threshold of 50% of the nominal input signal, where Nominal signal value is a block parameter. The motion is divided into three phases, equal in time: delay (t1), motion at constant acceleration (t2), and motion at constant velocity (t3). The motion stops when the switch-on time (ton) elapses. At this moment, the push-pin reaches the specified stroke value (xstr). To return the push-pin into initial position, the control signal must cross back through the threshold of 50% of the nominal input signal, which causes the push-pin to retract. The retract motion follows exactly the same profile but "stretches" over the switch-off time. Switching-on time and Switching-off time are the block parameters.
The transition in any direction can be interrupted at any time by changing the input signal. If motion is interrupted, the switch-on or switch-off times are proportionally decreased depending on the instantaneous push-pin position.
The push-pin is actuated only by positive signal, similar to the AC or DC electromagnets. The direction of push-pin motion is controlled by the Actuator orientation parameter, which can have one of two values: Acts in positive direction or Acts in negative direction.
Push-pin loading, such as inertia, spring, hydraulic forces, and so on, is not taken into account.
The push-pin stroke. The default value is 0.01 m.
Time necessary to fully extend the push-pin after the control signal is applied. The default value is 0.1 s.
Time necessary to retract push-pin from fully extended position after the input signal is removed. The default value is 0.1 s.
Sets the value of the nominal input signal. The output motion is initiated as the input signal crosses 50% value of the nominal signal. Other than that, the input signal has no effect on the motion profile. This parameter is meant to reproduce the rated voltage feature of an electromagnet. The default value is 24.
Specifies the initial position of the push-pin. The parameter can have one of two values: Extended or Retracted. The default value is Retracted.
In selecting the initial position, consider the following:
The steady-state push-pin position always corresponds to the control signal. In other words, zero or negative signal keeps the push-pin at Retracted, and positive signal — at Extended.
At the start of simulation, if there is a discrepancy between the initial position of the push-pin, as specified by the Initial position parameter, and the control signal, the push-pin immediately starts moving towards the steady-state position designated by the control signal.
Parameter controls the direction of the push-pin motion and can have one of two values: Acts in positive direction or Acts in negative direction. The first value causes the push-pin to move in positive direction, similarly to the action of electromagnet A attached to a directional valve. If the parameter is set to Acts in negative direction, the control signal causes the push-pin to move in negative direction from the initial position. The default value is Acts in positive direction.
The block has one physical signal input port, associated with the input signal, and one physical signal output port, associated with the output signal (push-pin displacement).
In the 2-Position Valve Actuator example, the hydraulic circuit contains two actuators. The first one is set to start from the retracted position, while the second one starts from the extended position. Both actuators are driven with a Pulse Generator. The actuators start extending at 1 s, but the second actuator first retracts from 0.01 m to zero, since it was initially extended and there was no signal keeping it there.
In the Hydraulic Circuit with Single-Acting Cylinder example, the 2-Position Valve Actuator block is used along with a 3-Way Directional Valve block to simulate an electrically operated 3-way directional valve.