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EMA Actuators Provide Smooth & Powerful Linear Motion

The EMA linear actuator range from Screw Jack has been developed to provide smooth and precise linear motion for low to medium duty applications with loads up to 10kN. These loads can be moved at speeds up to 5500 mm/min as standard with higher speeds available on request.

The design concept for the EMA linear actuators was to provide a compact unit, which delivered powerful, smooth and precise linear motion. The two main segments of the actuator is the "actuation unit" and the "drive unit".

The drive unit is based around a precision Spiroid gear set, which is a right angled/offset drive, consisting of a gear and pinion. The pinion is positioned in a different plane than the gear, which allows each shaft to be supported bearings on both ends. The pinion has a parallel screw form and has fewer teeth than the gear, which has a face type similar to a hypoid-offset spiral bevel. This arrangement offers a greater number of continuously meshing teeth (than for a worm gear of similar size). The high contact ratio provides higher strength, smoothness and quiet action from a compact design. This provides high quality rotary motion from the drive unit, which is transferred into linear motion the "actuation unit". As standard, the motors available for mounting on the gearbox are 3phase AC, 1phase AC or DC motors, with or without a brake. In order to maintain the compact envelope of the unit the motors have special drive shaft and face mounts, which are common for all motor sizes irrespective of frame size.

The actuation unit is based around a lead screw assembly, which converts the rotary motion into linear movement. As the screw rotates, the nut extends and retracts the ram, which is attached to the load. Two types of lead screw are used; a precision cut trapezoidal screw and nut for low duty applications and a high quality ball screw and nut for low to medium duty applications. The lead screw assembly is packaged inside a ram arrangement with guides and seals to provide a sturdy enclosure.

The actuator housing is designed to be compact, light and corrosion resistance. The ram has an aluminium outer tube and plated steel inner tube. The gearbox has a cast aluminium casing which closely follows the gear set profile for minimal envelope. Extra corrosion protection can be provided special paint finishes or materials.

The mounting options for the units are equally varied and flexible and include the classic double clevis and trunnion to clevis arrangements. As the majority of applications can be satisfied with a clevis end on the gearbox this feature is cast into the gearbox housing to keep the unit compact.

As the level of motion control varies on an application basis so to can the EMA actuators, which can have a wide array of devices fitted including; overload clutch, limit switches and encoders. The overload clutch is a device, which is mounted on the actuators ram, which will slip when the torque to drive the load exceeds the limit set. If the load is axially locked, or if a torque greater than the clutch setting is required to move the load, the clutch will disengage the load from the ram and prevent the motor from overloading the actuator components.

Within the range there are three defined sizes "I", "C" & "H" standing for Intermittent, Continuous and High Speed respectively. The "I" and "C" units both use the same gearbox type but with different lead screws, a trapezoidal screw in the "I" unit and a ball screw in the "C" unit. The "H" type uses a different gearbox, which employs a higher gear ratio to achieve the higher speeds. The gearbox housing itself has an increased surface area and mass for improved thermal duty rating. The "H" unit also uses a ball screw actuation unit.

Since prototype production the EMA actuators have undergone extensive tests both in-house and in industrial applications throughout the world. The actuators have proved successful even when operated to the extreme. Below are a few examples, which illustrate some of the wide range of applications in which the EMA actuators have been used:

• Dynamically balanced manipulators for handling radioactive materials. EMA actuators are used to move the slave arm relative to the master arm in a tilt and skew motion. The actuators are an integral part of the mechanism and act as load bearing struts, carrying the full reactive loads.
• Medium/heavy duty granulator two EMA actuators are used to raise and lower two sections of the machine to gain quick and safe access to the blades for maintenance.
• Rear door opening mechanism for armoured personnel carriers. A ruggedised EMA actuator is used to cope with extreme operating conditions including submersion in water.
  

Screw Jack Group
268# WenErXi Road , Fraserburgh
Aberdeenshire AB43 8TE
Scotland ( UK)

Tel: +44 (0) 1346 513131
Fax: +44 (0) 1346 516827
Email: [email protected]

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