**5. Conclusions and future research**

The basic hydrostatic transmission, composed by a volumetric pump and a hydraulic cylinder remains the most simple, compact and light mechanism for generating any force. The combination between a brushless motor, with digital driver, and a ball screw connected in close position loop became already the best driving system for small inertial loads, but the upper limit of the force remains low. The hybrid combination between a brushless motor and a hydrostatic transmission composed mainly by a high-speed pump, and a linear servomotor offers the best performances with the smallest weight and reduced dimensions. In the last decade,

**Figure 41.** *Voith industrial digital hybrid servomechanism [28].*

### *Hybrid Steering Systems for Automotive Applications DOI: http://dx.doi.org/10.5772/intechopen.94460*

a significant progress was achieved in promoting this new generation of compact actuators in all the modern industrial manufacturing process, different kind of steering system for airplanes, ships, trucks, the control systems for engines, turbines, ships, trucks etc. (**Figures 41** and **42**). The author's team created a new type of small power hybrid steering system dedicated to some type of heavy mobile robots. **Figure 43** presents a part of the test platform of the servopump [30]. A FPGA controller was designed for controlling the whole system. The exposure of the experimental results overcomes the frame of this paper.

However, some information about the components of the test bench built in the frame of the University POLITEHNICA of Bucharest can be useful for a better understanding of the design problems. An AC Servo Motor & Driver, MINAS A6 series produced in 2016 by Panasonic Corporation Motor Business Division was chosen for driving a reversible high-pressure gear pump XR012 from Vivolo Corporation.

A PXI industrial device from NI Corporation [20] controls the assembly by the aid of the LabVIEW real time environment. The hydraulic cylinder, designed by the authors for high mechanical efficiency, includes a tension and compression load cell Model 2712 – 500 from Sensy Company from Belgium; two pressure sensors type 7768202 from VIKA Company, and a linear displacement transducer type MLS130-200-R-N from Penny & Giles Company. Hydac Group and Bosch Rexroth Group supplied the hydraulic circuit components. After the first series of performance test, a cheaper dedicated controller was designed, and successfully tuned (**Figure 44**).

**Figure 42.** *Rexroth industrial digital hybrid servomechanism [29].*

**Figure 43.** *Servopump for hybrid servomechanisms designed in the Fluid Power Systems Laboratory of U.P.B. [30].*

#### **Figure 44.**

*Architecture of a configurable embedded controller for hybrid automotive servomechanisms [30].*

Anyway, the road to a mature industrial design will be a long one, and according to Dirk Hartmann and Herman Van der Auweraer from Siemens Corporation, it must pass through all the stages of the modern manufacturing process called now Digital Twins [31].
