Until recently, viable alternatives to hydraulic systems have been few and far between.
But as Bob Love, Assistant Branch Manager at THK reveals, recent developments in linear motion technology could change all that.

Channelling liquids through pipes and channels provides an ingenious method of harnessing mechanical force and, more importantly, controlling machinery. That said, hydraulics, the branch of science that deals with the conveyance of liquids to create control, has evolved almost beyond all recognition. Today, hydraulic systems are used in a variety of settings that extend from braking units on motorbikes to lifting equipment on industrial equipment. The level of control facilitated by hydraulic systems is such that it has even been used to provide the high-torque loads required by fairground rides.

While the principles that underpin hydraulic systems continue to evolve, alternative technologies are also emerging that deliver similar levels of control, although admittedly until recently at a price. Nevertheless, the advent of suitable alternatives has raised doubts over the suitability of hydraulics in some applications.

But what kind of technologies could replace hydraulics, and do they herald the decline of the conventional hydraulic system? While the theory supporting hydraulics has never been in doubt, there are now credible options that can deliver extraordinary levels of system control and safety at comparable prices.

Hydraulics
The phrase orginates from the Greek word hudraulikos, which is derived from the words hudro (water) and aulos (pipe). As such, this original interpretation describes the function performed by modern hydraulic systems perfectly.

Using pressurised fluids contained typically within a pipe, a hydraulic system can provide control over various mechanical components, including automatic transmissions, brakes, power steering, fork-lift trucks, tractors, industrial machinery and, of course, fairground rides. Pressure is applied to the fluid by a piston causing it to press on another piston which then delivers energy to a load. If the areas of the two pistons differ, then the force applied to the first piston will vary from the force exerted by the second piston. This creates a mechanical advantage, which is the factor by which a machine multiplies the force applied to it.

Typically, the fluids used in hydraulic systems are incompressible liquids made-up of different chemicals, of which the most common are mineral oils, organophosphate esters and polyalphaolefins. Unsurprisingly, many of these fluids can be harmful.

While the value of hydraulics is undeniable, the corrosive nature of some fluids employed ensures that an element of risk will always be present when using hydraulics. Similarly, due to the complexity of hydraulic systems, mechanical failure can’t be discounted, as a recent product recall by Mercedes-Benz aptly demonstrates. Reportedly costing the car manufacturer around US$30 million, the recall was needed to check a revolutionary braking system that relies on advanced electronics to control a high-pressure hydraulic reservoir.

As the automotive website TheCarConnection.com points out, it was a devastating blow for the German company. “The recall is particularly sensitive… because it involves the Sensotronic advanced braking system,” it noted. “A total of 680,000 Mercedes cars are being recalled worldwide.” The report concluded: “The system's hydraulic tank can develop bubbles that cause braking failure.”

In light of legitimate safety concerns and a desire to achieve even greater system control, many OEMs and retrofitters have considered replacing their hydraulic components with alternatives. One option is motor-driven linear guides and ballscrews.

Linear control
Linear motion in terms of load carrying LM Guides and Ballscrews as the driving devices, these combined products can be used in a variety of applications to provide control over machinery and components. Adaptable, reliable and accurate, these tough mechanisms can be installed on slopes, walls, level surfaces, vertical planes and inverted positions, and are available in a variety of styles.

Typically constructed of rails - or raceways - and guide blocks - or platforms – LM Guide units transport materials or components along specified routes. Suitable for any number of applications, linear motion guides have been adopted by a variety of manufacturing processes ranging from high-precision environments found in pharmaceutical and biotechnology research, to the harsh working conditions of industrial and process-orientated applications. More recently, they’ve become an economic alternative to conventional hydraulic systems.

Most linear motion systems use steel ball bearings held within the block to support the mechanism. These bearings run along a groove in the rail creating an efficient and precise movement. Like most technologies, this basic principal has been refined by successive generations wishing to incorporate the latest innovations. The result is greater efficiency and extraordinary performance levels. A relatively recent factor is THK’s Caged Ball™ design, which enables smoother movements, less friction and fewer maintenance requirements through retainers that hold the ball bearings at an equal distance from each other.

The latest innovations in linear motion technology have encouraged the use of linear motion guides in a range of sectors. The innovative use of ball screws and linear motion guides, for example, means these flexible components can be used in the most demanding environments, such as those found in theme parks.

Above the line
For years, THK has been at the forefront of low-cost actuators. The company’s latest foray into this market is its VLA motor-driven linear actuators, which are available in both cylinder and slider forms. Using miniature linear motion guides as the actuator’s base, both provide a viable alternative to hydraulics.

The VLA-CT cylinder-type actuator incorporates a feed rod driven by a ballscrew that exits the aluminium profile in a manner similar to that of a pneumatic cylinder. Correspondingly, the VLA-ST slider type is driven by a ballscrew that moves the slider on a Caged Ball linear motion guide.

Both units offer a number of benefits over traditional hydraulic solutions, including the elimination of noise and the requirement for fluids. Cleaner, quieter and more energy efficient, the VLA linear actuators offer movements of up to 1000mm/s, with a possible applied force of up to 402N. By reducing the number of components required to achieve these performance levels, the VLA actuators are also practically maintenance-free.

Closing lines
Hydraulic systems have been the cornerstone of modern engineering, but with environmental factors becoming increasingly prevalent and safety issues demanding even greater consideration, solutions incorporating linear-guide and ballscrew technologies are proving a viable and cost-effective alternative. By replacing hydraulic cylinders with linear actuators, fluids become unnecessary, noise is eliminated and efficiency increased. For many sectors, the period of hydraulic dominance is over.