Manual

A Digital control is either off or on, just like a light switch. A typical digital animation
movement is at either one end of its travel or the other, or moving between these two
positions
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. The speed of the action is set by the flow controls that control how fast the air
(or oil) can get into and out of the cylinder.
An analog control is like the light dimmer on the wall of your dining room. It can be off,
on, or at any point in between. The rate at which it is moving (within the maximum flow
limitations of the valve) is controlled by how fast you are turning the knob. If you stop
turning the knob half way through the rotation, the movement will stop there too. An
analog movement will follow every nuance of how you turned that knob during
programming and will be able to repeat it exactly. If something tries to push an analog
away from where it was programmed to be, it will actually fight to get back to where it
belongs.
How does it do this? Unlike open loop controls (digital movements are almost always
open loops), the command signal to an analog movement does not control the valve
directly. Instead, the command signal goes to some sort of Electronic Feed Back (EFB)
card. Examples of these are our EFB-Quad, PID-Quad and BS-EFB. Here the command is
compared with the actual position of the movement as measured by a device that is
mounted on the movement (typically a potentiometer). If the movement is off by just a
little, the EFB card will open the valve by just a little to get it back into the proper position. If
the movement is off by a lot, then the EFB card will open the valve as needed until it starts
getting close to where it should be. It then ramps the valve fully closed as the final position
is reached to slow the movement smoothly to a stop.
Despite their added complexity, analog functions tend to be more reliable than digital
moves. The reason for this is simple. Their closed servo loop allows them to adjust
themselves (within limits) to compensate for cylinder wear, leakage and pressure
variations. They are also smoother than digital functions. With less banging into the end
stops of the cylinders, there is simply less wear and tear on the mechanics of the figure.
The two most common failures in an analog movement are a break in the wires leading
to the feedback pot on the cylinder or a clogged valve. A unique feature of all of our
Electronic FeedBack cards is the ability to sense wire breaks, sound an alarm and to turn
‘off’ the affected axis until help arrives.
So why aren’t analog moves used for all animation? One reason. Price. The cost of the
cylinder and its associated hardware is virtually identical for an analog or digital
movement. The analog function does need a bit more electronic control, but this no
longer represents a major cost. The servo valve does. The cost of a solenoid valve for a
digital function might be between $20 and $30. The cost for a servo valve to do the same
movement as an analog would be in the $500 to $1000 range. In addition there needs
to be some sort of ‘feedback’ on the cylinder to tell the EFB card where the movement is at
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There are variations in digital movements that use more than a single digital valve or cylinder. These
allow some variation in speed and/or stopping mid stroke. With open loop controls, the repeatability can
not be guaranteed as it can with an analog function. It is also possible to use a pair of four way valves or
a single five way valve in a closed loop servo system. This will give you positional repeatability, but not
the smoothness you get from a real ServoValve.