Bosch Rexroth: Electrohydraulic motion update
Advances in electrohydraulic drives and motion systems—enabled by digital control technology, higher resolution sensors, and open bus interfaces—were highlighted in one of several “best-in-class” technology presentations at Bosch Rexroth’s “1st Global Technology Summit” in Lohr a.M., Germany, in late-January 2005.
|Bosch Rexroth electrohydraulic proportional valves integrate intelligence and networking functions.|
Advances in electrohydraulic drives and motion systems—enabled by digital control technology, higher resolution sensors, and open bus interfaces—were highlighted in one of several “best-in-class” technology presentations at Bosch Rexroth ’s “1st Global Technology Summit” in Lohr a.M., Germany, in late-January 2005. An electrohydraulic (EH) system comprises several elements: cylinder, integrated position sensors, high-response EH valve, and motion controller—which must be treated together as a system, explained Reinhold Schneider, product management, Industrial Applications at Bosch Rexroth, in his presentation entitled “Electrohydraulic System Technology.”
Automation of electrohydraulics drives requires physical considerations that differ from electric drives. EH valves’ nonlinear behavior requires selection of electrical components specific to the application. “The‘weakest element’ in the chain determines system limits and performance,” said Schneider. Special control algorithms also are needed to compensate for various effects, such as laws of flow, differential cylinder, valve characteristics, and closed-loop alternating position/pressure control.
Moreover, simulation via software plays an important role. Electrohydraulic system design benefits from the ability to obtain accurate simulated results of dynamic behavior before building hardware parts. Bosch Rexroth’s project planning software, HYVOS, helps select system components by simulating and analyzing results of different component designs and inputs.
Controls have the same feel
A machine operator cannot tell the difference between EH and electric drive system behavior because Bosch Rexroth uses the same controller, communicating with the same digital fieldbus networks; for example, Profibus, SERCOS, CANopen, or Interbus. Motion control functions can be integrated into an EH actuator, with savings in cabinet space and sensor wiring. However, the company also supports nondistributed control architecture for applications that still need cabinet-mounted electronics, added Schneider.
Positioning accuracy is another development advancing electrohydraulic controls. With onboard electronics, measurement signals are input locally in the actuator and the control loop is closed in the drive. Resulting EH-axis accuracies can be as fine as
Related new products mentioned include a proportional valve with integrated fieldbus (IFB) interface for sending commands or parameter changes and receiving diagnostic and maintenance information. The controller works in closed-loop and the EH drive in open loop. One application is in wind generators, to control blade pitch with reduced cabling and faster start-up (or replacement, if needed).
Another product, integrated axis controller (IAC), features closed-loop control of the valve aided by up to four pressure sensors and electronics integrated onboard. Here, the drive also has closed-loop control. An interesting application of IAC is in papermaking machines to compensate bending of calendar rolls. A high-response version proportional valve (IAC-R) adds an axis controller to the valve, along with closed-loop position control and friction/buckling compensation. IAC-R can also be controlled via an analog interface.
Working together, these technology advances are helping to reduce total cost of ownership for users of electrohydraulic controls, said Bosch Rexroth. “Hydraulics is well-known for its pure force, now it’s also intelligent.”
—Frank J. Bartos, executive editor, Control Engineering, firstname.lastname@example.org