Options for Straight Line Motion

November 5, 2007

5 Min Read
Options for Straight Line Motion

Motion control engineers want choices and linear actuator suppliers have responded. In addition to the usual design criteria of thrust, lead, resolution and accuracy, options range from having an integral connector and harness, sealed and covered protection, screw or belt driven, ball screw or leadscrew and more. The actuator designs demonstrate considerable variation, as well. From hybrid linear, rotary to linear converter to guides and stages, these motor-driven units provide engineers choices for designing linear motion systems.

ROTARY TO LINEAR MOTION

Zero Max Roh'lix linear actuators convert rotary motion into linear motion. Five sizes handle thrust from 5 to 200 lb. The actuators have shaft diameters from 3/8to 2 inch (8 to 50 mm) and leads from 0.025 to 6.00 inch (0.625 to 150 mm). Three precision ball bearings at each end of a two-piece aluminum block are mounted at an angle relative to the drive shaft axis. The bearings convert drive shaft rotation to proportional linear travel, called lead. The angle of the bearings in the block determines the lead. Friction between the surfaces of the angled bearings and the drive shaft determine the unit's linear thrust capability. With near zero backlash, the units provide up to 100 million inches of travel life.

HYBRID LINEAR ACTUATOR

When it added an integrated connector to its size 11 hybrid linear actuators, Haydon Switch & Instrument Inc. offered customers an option. The connector can be supplied with or without a harness assembly. Rated to handle up to 3A, the connector has a positive latch to ensure high connection integrity. The mating connector handles wire gauges from 22 to 28 AWG. The non-captive design has a 4-inch (101.6-mm) shaft and delivers up to 25 lb of thrust with resolutions ranging from 0.000125 inch (.003175 mm) per step to 0.002 inch (.0508 mm) per step. Targeting applications with space constraints or where direct attachment to an existing harness is important, the company will custom-design the motor for specific applications in addition to offering standard configurations.

SIDE-SEALED STAGE

Aerotech's ATS115 side-sealed stage design travels up to 600 mm at speeds within 300 mm/sec. Targeting medium-performance applications, the linear motion system has a hard cover for protection from debris. In addition, the side seals prevent dirt and particulates from entering the stage and protect the bearing surfaces from contamination. Vertical seal orientation deflects debris away from the stage instead of allowing debris to accumulate and cause sealing failures that can occur with a top-seal design. The unit's NEMA 23 flange-mounting interface allows the option of attaching a wide variety of the company's or third-party motors. For ease of integration, mounting holes in the stage's base are accessible from the outside. This avoids removing the cover to mount the stage or attach multiple stages together in an X/Y/Z system.

LINEAR GUIDE

The LM actuator Model GL-N from THK Co. Ltd. uses a light-weight, rigid aluminum base with caged ball LM guides for the guide portion. The drive system has the option of using either a screw or belt. The ball screw design has several leadscrew options and the selection of left, right and bottom motor directions for wrap-around motor types. With the timing belt design, a rigid timing belt enables high-speed processes with a longer stroke than the ball screw-driven type. The effective stroke of the ball screw design ranges from 100 to 1,550 mm for two different models and from 50 to 2,700 mm for belt-driven models. The SSR version addresses horizontal applications with a 90-degree ball contact structure in the radial direction, while the SHS version can handle radial, reverse radial and horizontal loads with 4-way equal load rating capability. The availability of a variety of flanges allows a wide selection of motor options for the guide. Other options include covers, bellows, sensors and cable carriers.

LINEAR STAGE

Hiwin Technologies KK linear stage is actuated by a motor-driven ball screw and guided by a linear guideway with a U-shaped rail. Several design choices include specifications for normal and precision modes. The slider functions as the ball screw's nut and the guideway's block. With rail lengths from 100 to 1,380 mm and a ball screw lead from 01 to 20 mm, the maximum speed range in the precision mode runs from 190 to 1,480 mm/sec and in the normal mode ranges from 390 to 1,050 mm/sec. Repeatability for precision modes units is typically ±0.003 mm, but for larger rail lengths increase to ±0.005 mm. In the normal mode, the repeatability is ±0.001 for most units. Accuracy ranges from 0.020 to 0.40 mm. Depending on the unit, starting torque can be a maximum of 1.2 to 15 Nm and in a couple of units slightly higher. Maximum dynamic loading ranges from 735 to 7,144N with maximum static load ratings from 1,538 to 1,2642N.

SCREW-DRIVEN ACTUATOR

Festo's DNCE electromechanical rod actuator uses either a ball screw or leadscrew and a non-rotating round piston rod for linear motion. Advantages of the ball screw approach over pneumatic actuators include higher precision and repeatability, higher feed velocities and longer duty cycles. The leadscrew-driven design includes self-braking for safety. With either approach, the motor can be mounted axially or reverse parallel for limited space applications. Slots in the housing allow easy installation of proximity sensors.

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