Growing together

March 2015

 

The electric motor and the hydraulic cylinder have been cornerstones in mechanical engineering for more than a century. Both yesterday and today, the details of the application are decisive – and drawing the best from the two technologies paves the way to pioneering solutions.

A long-held preconception was that the electric motor and the hydraulic cylinder were rivals. Many hydraulic experts saw electronic control components only as a complementary technology. Those advocating electromechanical drives, however, drew attention to their precision and energy efficiency. History shows that these two technologies served specific markets as a result of their specific potentials. Responding to new requirements, one development vector has been moving in the direction of merging the two. History also shows how important it was to set down the prerequisites for efficient interaction of the two technologies at an early date.

Maintenance-free three-phase motors with flange-mounted, low-backlash gears.

Maintenance-free three-phase motors with flange-mounted, low-backlash gears.

 

The application dictates the choice of drives

Reconstruction following the Second World War was in full swing in the 1950s and the new hydraulic excavators conquered the market. Their versatility and the high power density of the hydraulic drive technology used there were convincing. This rugged technology came to be a benchmark in heavy industry and for mobile construction machinery. This was a premier position that this technology has held to the present day. By comparison, machine tools used both electric and hydraulic drives early on. Hydraulic control was employed, for instance, in all the chucking and clamping processes while the machine’s spindle was driven by electric motors. In all-purpose machines, advancing was exclusively by hand. This all changed as CNC machines came to the fore. Here the feed motions also had to be automated and electro-hydraulic servo drives were excellent for doing this. Only with the advent of CNC machine tools was a fully novel drive solution needed to support the high performance data required. A competition among technologies followed, from which the permanent-magnet DC motor technology emerged victorious. It also proved that Rexroth, by putting its weight behind both the hydraulic and electric technologies, had made the right decision. Know-how already on hand made it possible to join in the competition at once. Even as early as the mid-1970s Rexroth developed its own series of DC servo motors and marketed them successfully. This was followed in 1979 by the world’s first maintenance-free, AC servo drive with brushless three-phase motor. Today the feed drives on CNC machinery use this technology exclusively, all around the globe.

Rexroth Sytronix – energy-efficient hydraulics with variable-speed pump drives.

Rexroth Sytronix – energy-efficient hydraulics with variable-speed pump drives.

 

Better together

Modern hybrid solutions satisfy the mix of requirements for real-world machinery systems with the assistance of both electrical and hydraulic technologies. They join the best factors from two worlds: efficiency, cost-saving, precision and dynamic response. One example is the Sytronix series made by Rexroth. There the pumps, motors and drive controls are so closely aligned one with another that energy losses can be avoided to a large degree. In addition, hybrid drives are ready for the future, since only the consistent merger of hydraulic drive elements, digital control electronics, and intelligent functions opens the way to integration into the networked world of connected industry.