Motors & Drives
Fig. 2. Yaskawa’s linear actuator is an all-in-one unit consisting of a linear motor, profile rails, linear guides, sliders, encoder and plug-in power electronics.
products. With a heavily patented technology and a form factor that offers a drop-in alternative to conventional pneumatic actuators, Festo believes its DNCE-LAS electric cylinders are attractive to design engineers seeking a performance advantage. Te DNCE-LAS electric cylinders offer fully
programmable, closed-loop position, acceleration and speed control, and are suitable for applications that demand extremely fast and accurate positioning capabilities. Te patented linear motors are based on an innovative tubular design, using high-flux annular magnets on the actuator rod, surrounded by a series of specialised windings on a long stator coil. Tis design is claimed to offer a number of significant advantages, including a low moving mass and no external magnetic field, thereby making the cylinders suitable for use in environments subject to swarf – such as in machine tools.
Tere is currently a choice of three 32mm profile models with stroke lengths of 100, 200 and 320mm, and four 40mm profile models with stroke lengths of 100, 200, 320 and 400mm. Te cylinders offer a variety of acceleration, speed and thrust ratings, with the largest model accelerating at up to 90m/s2
, achieving a maximum velocity of 3m/s,
and being capable of producing a thrust of 202N peak and 55N continuous. All seven models provide a positioning repeatability to within ±0.02 mm. Pressurised air cooling and pneumatic clamping options are available. A further innovation is what Festo describes as an
entirely new class of electric actuators employing a magnetically preloaded air cushion bearing to ensure very precise positioning and excellent linearity. Te ELGL-LAS linear motor uses a conventional linear synchronous design in which the stator takes the form
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of a fixed bed and the windings in the moving carriage are fed with drive signals from the motor controller. Te carriage features an integrated displacement transducer to provide digital position feedback to the controller. Up to three carriages can be used on the same bed simultaneously and controlled independently. In addition, the carriage contains a series of embedded permanent magnets to provide an integrated locking brake function; the carriage is only free to move when the air cushion overcomes the magnets’ attraction to the fixed bed. Furthermore, the use of an air cushion bearing minimises friction in the guide components, making lubrication and routine maintenance unnecessary. Tere are currently six models in the ELGL-LAS linear motor range; one has a standard stroke length of 1 metre, while the other five models provide double the stroke length and offer a variety of different acceleration, speed and thrust ratings. Te most powerful model can handle acceleration rates of up to 50m/s2
and speeds as high as 4m/s, and can produce a
continuous thrust of 349N, with a peak of 463N. All six models have a repeatability of ±0.01 mm. Tese specifications serve to illustrate some of the
key differences between the tubular linear motor and more conventional approaches. Tubular linear motors are certainly more dynamic, yet they cannot yet match the conventional technologies for stroke length. For short stroke lengths, however, there are two additional technologies to consider: piezo actuators and voice coil actuators. Piezo actuators rely on the piezoelectric effect in which a crystal changes its dimensions when subjected to a voltage. Even very high voltages correspond to only tiny expansions, so the technology is only suitable where short strokes are required, but the actuators can achieve extremely fine
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