Simulating Motion

The RMC can simulate motion on certain axis types. The axis simulates a physical system, including the feedback, and may be used to:

Learn how to move and tune an axis.
Develop and run user programs on your RMC before the machine is ready for motion.
Approximate a given real hydraulic system. This require advanced knowledge of system models. Set the Simulate parameters to values that correspond to your real system and then tune the simulated axis. This can provide an indication of the tuning values required for the real system.

Supported Axis Types
Position Control	✓
Position-Pressure Control	✓
Position-Force Control	✓
Velocity Control	✗
Pressure-Only Control	✗
Force-Only Control	✗
Reference Axes	✗
Virtual Axes	*

*Simulate mode does not apply to virtual axes. They have only a virtual target profile that can be commanded and have no physical inputs or outputs to simulate.

Notes:

During simulate mode, the axis' physical output is 0 V.
Simulate mode requires a physical RMC, and is not possible only within RMCTools.
If any axis is in simulate mode, the status of the Simulate Mode parameter is displayed in the Axis Status Registers Pane to clearly indicate that to the operator.
The simulated system will be limited to the limits of the simulated transducer. For example, if the Counts for a simulated MDT-feedback axis tries to go under 0 counts, or above 1048575 (16#FFFFF), a Transducer Overflow error will occur. If a voltage feedback axis tries to go below -10 Volts or above +10 V, a Transducer Overflow error will occur. To recover from a transducer overflow error, use the Direct Output (9) command to move away from the limit.

Setting up Simulate Mode

Use the Simulator Wizard to quickly set up an axis in simulate mode. It will set the simulator parameters, travel limits, and tuning gains so you can immediately move the axis in simulate mode. Axis parameters such as Linear/Rotary, SSI Data Bits, and Analog Input Type (±5V, ±10V, 4-20mA) should be set before using the wizard. Simulate mode requires a physical RMC, and is not possible only within RMCTools.

Enter Desired Position Range
Enter the desired range of position travel. For rotary axes, choose the number of position units per rotation.
Enter Maximum Velocity
Enter the desired maximum velocity. This is the velocity at which the axis will move with 100% of Control Output.
Enter Maximum Acceleration
Enter the desired maximum acceleration. This is not necessarily a true limit of the acceleration, but helps determine the response of the simulator and the tuning gains. For best results, set this value significantly higher than the acceleration rates you intend to use on the axis. This value is typically at least an order of magnitude (10x) greater than the maximum velocity.
Enter Pressure or Force Information
If the axis is position-pressure or position-force, enter the maximum force of the simulator, and the desired range of the force area at the ends of the travel.

The tuning of the pressure or force is affected by the position settings, especially the Maximum Acceleration. If the pressure or force tuning is poor, or pressure or force following errors occur, run the Simulator Wizard again and increase the Maximum Acceleration.
Review Parameters
Click Next and review the axis parameter settings in the Proposed column. Any parameters with blue text can be changed. When you are satisfied with the values, click Finish.
Download Axis Parameters
In the Axis Tools window, click the download button to apply the parameter changes to the controller.

After setting these parameters, make sure to enable the axis. This can be done by sending the Enable Controller (7) to the RMC. To do a basic move on the axis, send the Move Absolute (20) command.

Note: The simulator wizard will set the simulator to 2nd order.

Simulating a Real System

The simulator can be configured to approximate your actual system. The simulator parameters are in the Axis Tools, in the Axis Parameters, on the All tab, in the Simulator section. You will need to set the parameters listed in the table below. Use the guidelines below to calculate the Simulate parameters to approximate your real system:

Parameter	To calculate this parameter:
System Gain	The System Gain units are pu/s/V or pu/s/%, which is the speed the system moves for 1 V or 1% of control output. The RMC200 has individual Positive System Gain and Negative System Gain parameters to simulate different behavior in each direction of motion.
Simulator Order	The simulator can be set to 1st or 2nd order. A 1st order system is defined by the System Gain and Time Constant. A 2nd order system is defined by the System Gain, Natural Frequency, and Damping Factor.
Time Constant	For a 1st order system. To calculate the time constant, determine the time it should take the velocity to reach 95% of the steady state, and divide by 3.
Natural Frequency	For a 2nd order system. The Natural Frequency for a hydraulic system is normally between 1 and 30. Use the following formula to calculate the natural frequency for hydraulic system: Ω = sqrt[(4200000 A2) /(mass * volume)] where w = Natural Frequency (Hz) A = area of the piston (in2) mass = the mass moved by the system (lb) volume = the volume of trapped oil in the cylinder (in3)
Damping Factor	For a 2nd order system. The damping factor is a unitless number. Hydraulic systems typically range from 0.3 to 0.8. If the load has a lot of friction, this value will become larger. A lower value makes the system more difficult to control.
Positive Physical Limit	Specifies the maximum and minimum positions the simulator can move to. Notice that the Maximum Compression distance goes beyond these limits. Setting the limits both to zero means there is no limit. However, the RMC will simulate the feedback limit, whether it be counts, volts, or current.
Negative Physical Limit
Output Deadband	Simulates overlapped spools on hydraulic valves.
Output Null	Simulates a null offset on hydraulic valves.
Weight	Used to calculate the forces during motion.
Maximum Force	The max force of the system. Used when hitting the ends and in calculating the max speed.
Maximum Compression	The maximum compression at the positive and negative physical limits. This simulates a spring to provide pressure or force feedback.

Once you have calculated the tuning parameters, you must set the positive and negative travel limits and tune the axis according to the Tuning Position topic in order to move it.

Notice that on axes with analog feedback, if you move the simulated axis too far, it will turn on the Transducer Overflow bit.

Troubleshooting

Applying Simulator Parameters

For best results, always change the Simulator axis parameters only from Axis Tools.

RMC75 and RMC150: If the axis is in Simulate mode, and a simulator parameter is changed, the simulate model will be suspended until the last simulate mode parameter register (Max Compression [Fx:127]) has been updated. At this point, the new simulator model will be calculated and the simulator model will be activated. When the simulator model is suspended, the Actual Position will not move.

RMC200: The simulator parameters can be updated on the fly.

Simulator Unresponsive

In certain cases, the Actual Position may become unresponsive. One such case is if the Actual Position is moved such that the Counts become zero on a linear MDT, SSI, or Resolver axis.

If this occurs, you can reset the simulator by exiting and entering simulate mode:

In the Axis Tools, uncheck the Simulate Mode check box and download the axis parameters.
Check the Simulate Mode check box and download the axis parameters. The Actual Position will be set to the midpoint of the Positive and Negative Physical Limits.

Invalid Model

When the simulator parameters are changed, the RMC calculates the new simulator model for the axis. This can take several control loops to complete. The axis uses the model to simulate the motion. Due to the digital nature of the RMC, not all models are valid. It is possible for the model generation to fail due to more subtle interactions between the model parameters. Specifically, it is possible to have 2nd order models rejected if the Natural Frequency is near its maximum, especially when the Damping Factor is high.

If the simulator does not appear to be working, you may have an invalid model. Make sure the simulator parameters are within their ranges. The valid ranges are given in the help topics for each simulator parameter.