Rockwell Automation Integration

Overview:

The Kyntronics AOI was designed to make the integration of the Kyntronics actuator simple & easy. The AOI closes the loops in the PLC sending the appropriate speed signal to the drive. A virtual axis is used to provide motion commands to the SHA Axis, allowing the integration of the powerful RA motion commands.

Features:

  • Position Control
  • Force Control
  • Position or Force Control (switching at any time)
  • Position with Force Limiting
  • Multiple Gain Sets (for extend and retract)
  • Four Quadrant Control
  • Auto Tuning
  • Synchronizing Multiple Actuators
  • Integrated PanelView Press Interface (developed by Rockwell Automation)

Theory of Operation:

The SHA operates by directly coupling a motor to the bi-directional fluid pump. The motor is operated in velocity mode, and the motor encoder feedback is used to measure the velocity. Positive motor velocity MUST extend the actuator, and negative motor velocity MUST retract the actuator. The SHA_Axis->Properties->Polarity tab, Motion Polarity setting is used to change the direction, when needed. The pump pushes fluid, based on motor direction, to either extend the piston, or retract the piston. Lock Valves may be present, to act as brakes (a motor brake is not required to hold position). In other cases, Solenoid Valves are used to change the fluid path for High Speed / High Force combination products.

The actuator rod is often coupled to a position sensing feedback device, which is then provided as an input to the SHA_PositionControl block for closed loop Positional control. Pressure feedback sensors are used to calculate the Force. The SHA typically has an extend pressure sensor, or a retract pressure sensor, and sometimes both, depending on the application.

The SHA has two spring-loaded pressure relief valves (one for extend and one for retract), which will typically trip and open at around 3,000 PSI (207 bar) to protect the SHA. If the relief valve opens, the motor will continue to spin, as fluid goes through the opened relief valve, but the Force will drop, and likely the position will move “back” from the direction it was moving. If this “short circuit” pressure relief path is active, the SHA will demand excess torque and will heat up quickly and possibly damage the pump, so logic must be included to check for this condition. Some SHAs also have a thermo-switch included with the fan assembly connector, to report high temperature conditions which also needs to be integrated into the fault / shutdown logic.

Because the pressure relief valve is spring-loaded, it is also possible for high-impact situations to cause it to open, or partially open, momentarily, in these cases. This is one reason to enter the force zone slowly.

For single rod applications (majority), at the same pump speed, retract motion will move the rod faster than the extend motion, as the retract is moving fluid into the cylinder where the rod is located, so the volume is smaller than it is in the extend case.

AOI Rockwell HW interface

Recommended Hardware:

Since the SHA AOI is a motion control application, for optimal Force and Position control, Kyntronics recommends using a ControlLogix PLC, and local chassis 1756-IF4FXOF2F high-speed Analog modules for analog pressure feedback and/or analog positional feedback. Do not use network/remote analog inputs for the SHA feedback otherwise performance may be degraded.

> If a CompactLogix PLC must be used, then use one that has a 64-bit processor (not a 32-bit processor) and use local chassis mounted 1769-IF4FXOF2F fast analog input module(s).

> 1-2 millisecond Logix scan rates are recommended.

> For fastest analog input conversion times, set the digital filter time to 0 ms, and enable the Synchronize Module Inputs and set the RTS to 1 ms. Set the module for 1 ms Requested Packet Interval.

> RA rule of thumb in CIP architecture: 32 axis/ms of group update rate.

> Kinetx CIP (EtherNet/IP) drive recommended: 5700, 5500, 5300.

> Use the 5700’s ½ axis TTL input for the linear position (for higher precision requirements).