Designing a two-axis position stage could be a challenging thing. Simplifying the design makes assembly easier and increases reliability by reducing the number of parts that can finally fail. One way to simplify the design is to use a linear stepping motor with only one moving part. It provides an alternative to automatically complex assemblies that require regular maintenance and develop inaccuracies over time.
Dual-axis linear stepping motors are comparatively simple consisting of a stepping motor primary called the forcer, and a stepping motor secondary called the platen. The forcer consists of four single-axis coil assemblies, two of which are mounted at 90° to the other in a basic housing. One set of coils drives the forcer in the X axis direction and the other in the Y axis direction. The surface of the platen is a steel square tooth pattern with the spaces between the teeth filled with epoxy. The platen surface is then lapped up to a precision flatness. Tooth pitch determines the resolution when either full stepping or microstepping the motor. Increasing the number of motor phases also increases motor resolution.
The forcer drives on top of the platen surface via a pneumatic bearing system. The air bearing consumes roughly 2 cfm of air at 50 to 60 psi. The flows of air into a 0.25-in. fitting on the side of the moving forcer and is evenly distributed through precision orifices on the bottom surface of the forcer between it and the platen. The forcer is constructed with rare-earth magnets which preload the air bearings to the steel platen with up to 350 lb of attraction force. This allows the stepping motor to be inverted without the forcer separating from the platen.
The stepping motors can be operated either open or closed loop. Open-loop accuracy is 0.0004 in./6 in. with one-way repeatability of 0.00001 inch. absolute. It's also a common practice to profile the motor forcer and platen producing a map for software error compensation when running open loop. Mapping increases resolution and accuracy and offers an alternative to closed-loop operation.
Closed-loop accuracy and repeatability will depend upon the type of position feedback selected. However, resolutions and accuracies of less than one micrometer are attainable. Compact laser interferometers and vision systems are often used for position feedback.
The dual axis stepping motors are capable of creating forces to 30 lb and carrying payloads up to 100 lb. Light payloads can be accelerated to 1.5 g's. Because of the rare-earth permanent magnets in the forcer that preload the pneumatic bearing, the motor can be inverted allowing the payload to hang below the motor. Additionally, multiple forcers can share a common platen providing a compact multiaxis assembly with overlapping trajectories.
OSM' Linear Actuators are suitable for precision linear motion in applications such as medical equipment, bar-code scanning devices, printing equipment, laboratory instrumentation, and mechanisms requiring high force.
Three designs are available, captive, non-captive and external linear actuator versions. We can customize the winding to perfectly match your voltage, current, and maximum operating speed. Special lead screw modifications, cables and connectors are also available upon request.
Established in 1992, OSM Technology Co.,Ltd. began as a consulting company specializing in Stepper motor applications. Throughout its history, OSMTEC has continued to develop its capabilities in the areas of design engineering, manufacturing, and customer service. In 1995, OSMTEC expanded its operatings to include the manufacturing of its own Hybrid Stepper Motor. Since then, the company has developed its product line to include Linear Actuator and Brushless DC Motor.
Our operations are certified to ISO 9001:2000 and QS 9000. All products carry major approvals such as CE and ROSH. With OSMTEC Technology, you get the highest quality products, all made possible by the most dedicated people.
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