Using an External Target Generator

Some applications require that the target generator be external to the RMC. This target generator may be a PLC, a signal generator (such as an oscillator), or a joystick. Joysticks are discussed in more detail under Using Position and Velocity Joysticks.

Using an external target generator requires the following components:

The target generator must provide an analog signal in one of the formats supported by the RMC’s analog modules (0 to 10V, ±10V, 0 to 5V, ±5V, and 4 to 20mA).
A channel on either a 12-bit or 16-bit RMC analog module must be assigned to be the reference input (you must select position, velocity, or pressure reference).

Note: The reference input may also be any other axis type, even one that is controlling its own axis. The reference input is unaware that another axis is gearing to it.

An axis (it may use any supported transducer type: quadrature, MDT, or analog) must be configured to control the same item as the reference input (you must select position, velocity, or pressure control; MDT and quadrature axes are always in position control).
The control axis must be slaved to the reference input.

Step-by-Step External Target Generation

Follow these steps to set up a system using an external target generator:

Assign the Analog Axes

Each of the channels on the analog module(s) must be assigned to a role. The reference input must be assigned to one of the three reference types (position, velocity, or pressure). Refer to Analog Transducer Configuration for details on assigning channels.

Configure the Reference Input

Analog inputs must be configured to select the type of the input. These options include 0 to 10V, ±10V, 0 to 5V, ±5V, and 4 to 20mA. See Analog Transducer Configuration for details on setting this value.

Configure the Control Axis

See the configuration topic of the transducer type you are using.

Determine the Position Units and Limits of the Reference Input and Control Axis

Use the Scale and Offset parameters to select position units on the reference input and control axis. Remember that these position units will be used in the gearing ratio defined in step 6.

Initialize the Control Axis and Reference Input

Send the above parameters followed by a Set Parameters (P) command to the control axis and reference input.

Slave the Control Axis to the Reference Input

Use the Go (G) command to configure the control axis as a gearing slave. This is done by setting the Gearing bit in the Mode command field, and the numerator and denominator of the gear ratio in the Command Value and Speed command fields of the Go command. For details on Gearing, see Gearing Axes.

Note: This does not align the control axis with the reference axis. It just ensures that any further moves of the reference input will cause the control axis to move the same amount adjusted by the gear ratio. You must use a separate move command to align them.

Example:
Suppose you scaled the reference input so it will move between 1,000 and 10,000 position units. You want the control axis to be geared to the same range. However, after you do steps 1 through 5 the positions of the two inputs will most likely not be equal.

For example, assume the reference input's actual position is 1,500 and the control axis's actual position is 5,500. If the axes were geared together at this point with a 1:1 ratio, then the control axis's position will always remain 4,000 position units higher than the reference input's position.

Therefore, you will need to move the control axis's position back to match the reference input's position before gearing them. The simplest way is to use one of the Move Relative to An Axis (0xC0-0xCF) commands to move the command axis relative to the reference input.