Electromechanical linear solutions replace hydraulics and pneumatics
By Jennifer Sachs
In a wide range of industries, there is a growing trend to substitute hydraulic and pneumatic drives with electromechanical alternatives. The industry where it is most evident is aerospace, where the fly-by-wire concept has meant a replacement of...
In a wide range of industries, there is a growing trend to substitute hydraulic and pneumatic drives with electromechanical alternatives. The industry where it is most evident is aerospace, where the fly-by-wire concept has meant a replacement of many hydraulic systems with electromechanical actuators.
Similarly in the automotive industry, hydraulic brake, clutch and steering systems may well be substituted by the electromechanical actuators of drive-by-wire technology. The concept cars Filo and Novanta, developed by Bertone and SKF, are impressive examples of how virtually all functions fulfilled up to now by hydraulic components can be carried out by smart electromechanical actuators, providing reliable and environmentally friendly operation.
Engineers often believed that electromechanical linear systems could substitute for hydraulic systems only in the low load range. This is no longer the case, a perfect example being the E-Truck, a fully electric concept fork-lift truck with a lifting force of 3.5 tonnes, presented by SKF at a Hanover Fair in Germany.
Also, electromechanical drives are gaining ground in production machinery. Spot welding and riveting machines, which have traditionally used pneumatics, are increasingly being replaced by electromechanical alternatives. Even in injection moulding, where injection, ejection and clamping processes were generally actuated hydraulically, now all-electric machines are continually gaining market share.
This development is due to the benefits the electromechanical systems offer. These are:
Low environmental impact: When no oil is used, neither leakage nor disposal of the used oil can present a problem. There is no risk of harmful fluid escaping in the event of seal failure.
Economical production: Thanks to reduced maintenance and higher quality of the output, machine productivity increases. This high productivity, together with cleanliness, makes electromechanics the system of choice for the manufacture of electronic components, which usually takes place under clean room conditions. In the past 20 years, this sector showed continuous growth for electromechanics, parallel to the development in the electronic industry.
Simple control: Fluid systems must cope with control difficulties due to the compressibility of the medium used. Electromechanical systems eliminate this problem.
Precision: Digital position feedback from sensors makes micron-level positioning possible in electromechanical systems. The machine accuracy is further enhanced by the high stiffness of electromechanical solutions.
Simple and reliable design: Electromechanical systems need neither pipes nor tanks for the operating medium. Especially, ball and roller screws fulfill stringent requirements in terms of clean operation and low life-cycle costs. This is due to the low level of maintenance required, as they require neither oil nor filter change nor replacement of valves or seals. Furthermore, electromechanical systems have a low noise level and are easy to install and commission, which makes them the ideal assemblies for plug-and-play solutions.
Energy savings: In terms of energy costs, electromechanical systems outperform hydraulic and pneumatic drives, as they only use power when the motor is running. The pumps of hydraulic systems, in contrast, must operate continuously, making them less efficient. Pneumatics and hydraulics go through a two-step energy conversion, preventing them from achieving the high degree of efficiency of 80% to 90% that is typically offered by ball and roller screws.
Nevertheless, electromechanical alternatives to conventional hydraulic and pneumatic systems still cover only a rather small share of all potential applications. The reason for this is that electromechanical drives are not always considered feasible by engineers in applications with extreme loads or long strokes.
Yet with computers and electronic controls now commonplace in most industries, costs are falling and the way is being paved for easily programmed electromechanical actuators. Also, the integration of roller screw technology means that more and more of the high-load applications that previously required hydraulics can now be successfully replaced with electromechanics.
A recent SKF development in electromechanics is in compact cylinders, which provide high load-carrying capacity in a particularly small package. A wide standard cylinder range offers plug-and-play solutions for loads up to 19 kN, with instantaneous acceleration and speeds up to 450 mm/s, higher loads and speeds also being possible. If required, the electromechanical cylinders can be supplied complete with limit switches and electronic controls. The result is a powerful package that requires approximately 40% less space than traditional designs.
In co-operation with a manufacturer of spot-welding tongs used in automotive manufacturing robots, SKF developed an optimum solution to replace a pneumatic actuation system. The requirements were clear. The solution should have high stiffness and precision to ensure high-quality welds, be clean and quiet, use little energy and require little maintenance.
Equally important is precise and careful positioning of the electrodes, as this affects the service life of the electrodes. If the welding gun closes too hard, it may result in undesirable sparks. The solution must also be robust. The robots weld 35 spots per minute, and the tongs are designed for a life of over 10 million welds.
Within just a few months, SKF developed and manufactured prototypes, and since September last year two variants of the welding guns in series production have been equipped with the SKF solution.
Another example that highlights the benefits of electromechanics is the replacement of the hydraulic system in horizontal broaching machines. A manufacturer of bushings wanted to increase the efficiency of production by changing over the drive system. The machines work 20 strokes per minute, operating 24 hours a day, and are designed to have a service life of at least 10 years.
By replacing the hydraulic cylinder and system with an electromechanical actuator and control, piping and oil tanks were no longer necessary. This greatly improved access to the machines and simplified any maintenance work. Product quality and repeatability of the machines were enhanced, and a productivity increase of 20% achieved, translating into about two million additional pieces per year. Furthermore the customer has estimated that it will save over E2,000 in energy costs per machine.
To date, two other machines have been retrofitted, and the customer is looking into the possibility of also changing to electromechanics for all its other broaching machines.
Electromechanical solutions are already being used in a large number of industries as mentioned here, but the trend doesn’t stop with them. With electronic controls becoming more cost-efficient, and powerful and environmental regulations becoming tougher, electromechanical drives will be increasingly used.
This is being experienced today in new projects in the printing industry, food industry, steel industry and also in marine applications such as in the opening and closing of sub-sea valves.
Though it is still early, as the technology progresses, it is logical that even the industries that have a long tradition of using hydraulics, such as construction, agriculture and forestry, will also be looking to take advantage of the benefits offered by smart, electromechanical systems. MRO
Jennifer Sachs is with SKF Canada Linear Motion and Precision Technologies, Scarborough, Ont. For further information, visit www.skf.ca.