New at OTC (Offshore Technology Conference) earlier this month was a new self-contained electrohydraulic actuator from Bosch Rexroth, which reduces space and weight by eliminating external piping for heavy-duty loads.
As the device demonstrated its powerful lifting capabilities (in the short clip below), Tor E. Jensen, Director Oil & Gas and Marine, Bosch Rexroth, explained how the system is different from standard hydraulic cylinders that require an external power unit and pipes all over the place. “Here everything is integrated into one package, which means it’s a self-contained hydraulic actuator. All the oil is enclosed in the cylinder, in the accumulators, in the pump and the valves, so there is no external piping necessary. It’s closed to basically no leakage, and is servomotor driven, so only consumes energy when you need it.”
Tor explained also that for loads up to 20 tons, electromechanical solutions are best but when it comes to heavier loads greater than 20 tons, it’s a must to switch to the power density offered by hydraulics.
These stand-alone axes from Bosch Rexroth with identical servodrives for actuators with mechanical or hydraulic force transmission offer new degrees of freedom for machine manufacturers. The versions with hydraulic transmission are provided with their own, decentralized fluid circuit. The installation, commissioning and connection to controls and Industry 4.0 environments via a Multi-Ethernet interface or ProfiBus are identical on both variants.
The stand-alone self-contained electrohydraulic servo axis largely consists of electrical and hydraulic series components. They pair all the functions known from servodrives with the physical advantages of fluid power technology such as high power density and robustness. The standardized sub-assemblies—hydraulic cylinder, control block and motor/pump group—form the basis for these linear axes of modular design. They are fitted with their own, closed fluid circuit and do without a central hydraulic power unit. The leak-free fluid circuit requires only a very small amount of hydraulic fluid. Bosch Rexroth delivers the axes completely preassembled, filled with hydraulic fluid and commissioned. The system is virtually maintenance-free and the fluid medium service life corresponds to that of the axis.
Each stand-alone axis includes Rexroth IndraDrive servodrives, with a power spectrum of up to 630 kW. Thanks to their decentralized intelligence and standardized software, the type of force transmission is irrelevant for the higher-level control. Also when it comes to commissioning, there is no difference. A power connection and a communication connection to the higher-level control are sufficient. In addition, IndraDrive controllers with their Multi-Ethernet interface support all common Ethernet protocols like Sercos, ProfiNet, EtherNet/IP, EtherCAT, Powerlink or ProfiBus.
The software of the IndraDrive servodrives assumes the control of the linear unit. The SHA library contained in the software automatically takes account of all specialties of fluid power technology. This allows the user to easily parameterize even complex travel profiles, for example for forming and joining technology, injection molding machines and other applications that involve large forces. Apart from the standard function “Safe Torque Off,” IndraDrive drives offer further certified safety functions. With the help of “Safety on Board,” which is integrated in the drive, machine manufacturers can reach safety levels up to SIL 3 according to IEC 61508, which corresponds to PLe according to IEC 13849.
Bosch Rexroth’s stand-alone self-contained electrohydraulic servo axes are characterized by high energy efficiency. If temporarily no movement is required, the servodrive lowers the motor speed for the pump in-line with the demand in partial-load operation or switches to stand-by mode. Power branching in multi-axis operation is accomplished purely electrically. The controllers recover braking energy and can make it available to other consumers via an intermediate circuit. In addition, it is possible to store the recovered energy or feed it back to the mains.
For the rating of the SHA in line with application requirements, Rexroth developed a simulation program on the basis of experience in modeling of hydraulic systems gained over decades. This software tool shortens the time to market and offers machine manufacturers higher safety in the engineering phase.
Thanks to the modular design of the SHA with standardized sub-assemblies, the machine manufacturer can easily adapt the axis exactly to his application. SHA from Rexroth covers the power range from 100 to 2.500 kN in pulling and pushing direction. The maximum stroke of the axes, which feature protection class IP 65, is 1,800 mm. With an integrated, magnetostrictive absolute encoder, the accuracy is 1 μm.