Product category:
Process and OEM Valves
News Release from: Moog Controls | Subject: DIV
Edited by the Engineeringtalk Editorial
Team on 03 December 2002
Proportional valves benefit from digital
control
Affordable processing power has been strategic in allowing the migration of digital closed loop control technology into the heart of hydraulic servo actuation products.
Affordable processing power has been strategic in allowing the migration of digital closed loop control technology into the heart of hydraulic servo actuation products The most recent developments have been within the control valve itself and are already paying dividends, for example: improved performance characteristics; rapid customisation to suit application needs; and user adjustability of key valve parameters
This article was originally published on Engineeringtalk on 17 Apr 2008 at 8.00am (UK)
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The issues of standardisation and modular design have also played a big part in shaping the valves of the future.
The Moog DIV digital interface valve provides an example of the new technology in action.
The name DIV is in reference to the CANopen communication protocol used to replace (or complement) the conventional +/-10V or +/-10mA analogue interface.
However the onboard 32bit floating process allows for much more than this.
At the core of the valve, digital technology is used to shape the motor current driver and provide smart algorithms for more effective handling of the motor and spool flow force characteristics.
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If the two hydraulic rams were allowed to operate without a control system to keep them in balance, the whole system could easily tip over.
The digital spool position loop includes improvements to the active damping control to ensure faster and more stable operation under all conditions.
The inclusion of an onboard pressure transducer (optional) and PID closed loop controller allows the same valve to be used in any one of three operating modes: Q - flow P - pressure; or P/Q - flow, with pressure limiting These features make the DIV ideally suited for the control of position, speed, load or power applications.
Further to the basic control function the DIV is equipped with many additional features including: dead-band compensation; demand ramp generation; demand level limitation; dual gain characteristic; logic interface; and error and status display.
The commissioning engineer has full authority to change the parameters related to any of the above features in addition to the usual closed loop tuning gains.
Communication via CANopen, whether from a host system in real time, or via the PC based user interface, conforms to the internationally recognised Fluid Power Device Profile.
This was first proposed by the VDMA organisation in Germany and is now covered by CiA Standard DSP 408.
At a user level the standard specifies an open architecture for valve parameter definition covering all of the features described above.
The CiA standard (via CANopen) also defines the message handling protocol over the bus link,and even gives details right down to the cable and connectors to be used in the installation.
Moog has chosen CANopen for loop closure applications because of the high integrity in message handling, the high speed of data transfer and the robust way of handling both configuration and real-time operating signal messages.
The DIV valve configuration tools are PC based and provide easy access to all of the valve parameters along with numeric and oscilloscope displays, status information and the means of saving and downloading configuration settings.
The real benefits of the DIV in operation can be seen when comparing it with more conventional installations.
For example, take the case of a closed loop pressure control installation.
Conventional pressure control applications include an external pressure sensor, external PID control card and various racks and cables.
In some cases long cable runs may be necessary introducing the additional problems of noise immunity.
All of this disappears with the fitting of a single DIV valve.
In the case of position control applications - or where other (external) sensors are involved - the CANopen approach gives further installation savings.
In this case, all of the devices may be handled over the CAN link with some closed loop functions being implemented at the host controller over CAN.
The DIV has been well received in the market and has brought the benefits of the new technology to an increasing number of installations.
For example the DIV has been successfully installed in paper machine and wind turbine applications.
In the former, multiple valves are used in pressure control mode to regulate internal roll bending as a means to achieving paper uniformity.
In wind turbine applications, the DIV is taking care of blade pitch control.
CAN message handling via slip rings is proving to be a good way of alleviating the normal problems of analogue signal transmission. Request a free brochure from Moog Controls ...
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