Axis Types

The axis types listed in this topic are available on the RMC.

What is an axis?

An axis is a combination of inputs and/or outputs in one single entity, and includes all the necessary motion features for those inputs and/or outputs, which can include feedback scale and offset, filtering, control algorithms, output scaling, etc.

The major types of axes available in the RMC are:

Control Axis:
Has one Control Output and control either zero, one or two feedback quantities, such as Position, Velocity, Acceleration, Pressure, or Force.
A control axis with no feedback quantities is called an Output Only axis.
Reference Axis:
Has an input for transducer feedback and does not have a Control Output. A reference axis is not capable of controlling a system. Reference axes are commonly used in gearing, synchronization, or monitoring applications.
Virtual axis:
Has only a virtual target position (with velocity and acceleration) with no feedback or control loop. Typically used as a gear or cam master.
Cascading Outer Loop:
A control axis that provides a virtual Control Output, and does not use a physical Control Output. For more details, see the Cascade Control topic.

Counting Axes

Any axis in the RMC counts as one single axis, regardless of the number of inputs or outputs. For example:

A position-force application may require one analog position input, two analog pressure inputs, and 1 output, and is considered one axis.
A reference axis with only one input is considered one axis.
A virtual axis has no feedback or output and is considered one axis.

Supported Number of Axes per Controller

RMC75

RMC150

RMC200

CPU20L

RMC200

CPU40

Max Control Axes1

Max Total Axes, including Virtual, Reference, and Outer Loop

128

1 For the RMC75 and RMC150, Control Axes includes Output Only axes. For the RMC200, Control Axes does not include Output Only axes.

Note: It is possible to add more analog inputs on the RMC75 than can be assigned to axes. However, it is still possible to view the voltage of the extra analog inputs using the Analog Input Registers. Inputs that are unassigned to axes can have no status bits, error bits, scaling, filtering, etc.

Axes and Loop Time

The number of axes for each RMC is limited depending on the specified Loop Time. See the Loop Time topic for details.

Axes Physical Feedback Types

The RMC supports the physical feedback types listed below. Notice that any type of feedback (e.g. torque, temperature, etc.) can be controlled if the transducer is compatible with the RMC.

Any of these feedback types can be used as part of a Control Axis, Reference Axis, or Cascading Outer Loop axis.

Feedback Type	Transducer Type	Supported Transducer Output Types
Position Notice that a position feedback control axis can also control velocity.	position	MDT
		SSI
		Quadrature
		Resolver
		Analog Voltage or Current
Velocity	tachometer	Analog Voltage or Current
Acceleration (single- or dual-input)	1 or 2 accelerometers	Analog Voltage or Current
Pressure	pressure sensor	Analog Voltage or Current
Force (single-input)	load cell (±10V, 0-10V, ±5V, 4-20mA)	Analog Voltage or Current
Force (single-input)	load cell (mV/V)	Millivolts/Volt
Force (dual-input, differential)	2 pressure sensors	Analog Voltage or Current

Custom Feedback

An axis' feedback can be defined as custom, which requires creating a user program to continuously calculate the feedback value. This allows for using the sum, difference, or average of other transducers as feedback. It also provides for switching feedback on-the-fly, redundant feedback, and feedback linearization. For details, see Custom Feedback.

Dual Loop Control

The RMC supports dual-loop control. This is typically used for controlling two quantities, such as position and force, with a single actuator. See the Dual-Loop Axes topic for details.

Feedback Type	Description
Position-Pressure	Used for controlling both position and pressure with one actuator. Typically used with hydraulic cylinders.
Position-Force	Used for controlling both position and force with one actuator. Typically used with hydraulic cylinders.
Position-Acceleration	Used for advanced control such as active damping, which provides precision control of difficult systems, such as pneumatic systems.
Velocity-Pressure	Used for controlling both velocity and pressure with one actuator.
Velocity-Force	Used for controlling both velocity and force with one actuator.
Velocity-Acceleration	Used for advanced control applications.

Defining Axes

The user has full control over how the inputs and outputs on the Axis Module and the inputs on the Expansion Modules are assigned to axes.
See the Defining Axes topic for details on assigning axes to the hardware.

Other Axis Types

In addition to the axis types listed above, further distinction can be made between axes:

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