Valve linearization refers to compensating for non-linear hydraulic valves.
Delta does not recommend using non-linear valves for motion control if a linear valve is available. When using a high-performance motion controller, there is usually no reason to use a non-linear valve. Linear valves will perform better than non-linear valves, even with valve linearization. Non-linear valves are typically only useful for valves directly controlled by hand controls, such as a joystick.
Single-Point Valve linearization
The RMC75 and RMC150 motion controllers provide single-point valve linearization to compensate for valves with one sharp "knee" or "kink" in the flow versus command signal diagram, as shown in the Single-Knee Valve diagram below. This valve linearization typically results in a drastic improvement in control. Using this method for other non-linear valve types will provide some improvement, but will not provide optimum control.
To Apply Single-Knee Valve Linearization
In the Valve Linearization Type cell, choose Single-Point.
In the Knee Command Voltage cell, enter the voltage value of the knee. This voltage can be obtained from the valve data sheet. For example, in the Single-Knee Valve diagram above, the voltage is 4 volts.
In the Knee Flow Percentage cell, enter the flow percentage of the valve at the knee. This value can be obtained from the valve data sheet. For example, in the Single-Knee Valve diagram above, the flow percentage is 10 %.
Download the changes and update Flash.
The valve linearization is applied only when the axis is in closed loop control.
Linear and non-linear refer to the flow versus command signal profile of a valve.
Linear valves have a profile where the flow of the valve is linearly proportional to the command signal input. The diagram should look like this:
Non-linear valves have a profile where the flow of the valve is linearly proportional to the command signal input. Common types are single-knee, and curvilinear. The RMC motion controllers provide single-point linearization for single-knee valves.
Affect on Control
The motion controller's PID control algorithm expects that the hydraulic axis will produce a velocity that is linearly proportional to the Control Output voltage, which a linear valve does. If the velocity is not linearly proportional—such as in a non-linear valve—the gains will not be able to achieve optimum control. This especially affects the Velocity Feed Forwards, which depend on a linear relationship.
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