Positioning Systems & Actuators
Positioning Systems and Actuators are the part of a motion control system that produces the desired motion. An actuator is a device that creates physical movement by converting various forms of energy to rotary or linear mechanical motion. A linear actuator is defined as a device that converts various forms of energy into linear motion. Actuators (electric cylinders) are mainly thrust producing devices that use either an acme or ball screw as the driving mechanism.
Positioning systems are compact, easy to use, and are designed for turnkey operation. Most preconfigured positioning systems employ a rigid base, ball/acme screw, and servo/stepper motor with integral controller + drive for rapid machine commissioning and ease of operation.
Rotary Stages use a precision machined worm gear assembly and either ball, cross roller, or angular contact bearings to support the table top load. The selection of different gear ratios allow for either high resolution or high speed in a low profile package. The use of any step motor or servo motor system to drive rotary tables is a key advantage since it allows the use of a preferred motion control system.
Types of Linear Actuators View More
- Screw Actuators:
- Lead screw actuators: - A lead screw actuator with a threaded nut that moves with a screw. It provides both simple construction and lowest cost.
- Ball screw actuators: - A lead screw actuator that uses ball bearings; more expensive but less friction compared with lead screw actuators.
- Planetary roller screw actuators: - A lead screw actuator that uses threaded rollers surrounding the main threaded shaft; the most expensive option but also the most durable.
- Actuators based on belt drives; often used where speed is important but with limited accuracy.
- Rod type: - The thrust element or rod moves out of the end of the actuator as motion takes place; produces more force and highly tolerant of dirty environments but require a bearing structure to carry the load.
- Rodless type: - The actuator housing completely surrounds the screw which provides a load bearing and guidance structure. Rodless actuators are difficult to seal for dirty or wet environments.
- Integrated Actuators integrate a rod style actuator into a motor housing to eliminate the need for a coupling. Integrated actuators provide the lowest size and weight and provide easier maintenance but are typically higher cost.
Types of Positioning Systems View More
- Screw Driven Positioning Stages:
- Screw driven positioning stages are used in applications where accuracy & repeatability are more critical than axial thrust forces. The base, carriage, and all sub-assembly components are precision machined which contribute to the accuracy and repeatability of the stage. These positioning tables use either an acme or ball screw as the drive mechanism. Ball & rod, cross roller, round rail, or square rail linear bearings are used to carry the user load. These linear bearing designs allow the user load to be positioned very accurately & repeatedly.
- Belt driven positioning tables are used in high speed (and/or long travel) positioning applications where a screw driven stage is not practical, usually in stroke lengths over 6ft. The belt & pulley drive mechanism, along with either round rail or square rail linear bearings, provide a modestly repeatable high speed positioning table. Unique to belt driven positioning stages is their ability to provide the same speed capability independent of travel length.
- High Accuracy Positioning Tables/Nano Precision Stages are used in applications where high accuracy and repeatability and/or smoothness are critical. All sub-assembly components are machined to very tight tolerances in order to achieve the required accuracy and repeatability. Typical precision for these types of stages are measured in the sub-micron or nanometer range. Precision ground acme screws, precision ground ball screws, or brushless linear motors are typically used as the driving mechanisms for these stages. Precision ground cross roller bearings, ultra high accuracy square rail bearings, or air bearings are mainly used for the linear bearing system. Granite or a precision machined steel plate is commonly used for the table mounting surface. A temperature controlled environment, machine shock absorbers, and high resolution linear encoders are also usually required in order to obtain and maintain the system accuracy and repeatability over the life of the product.
Positioning Systems Comparison ChartView More
|Power Density||High||Low||Med. to High|
|Installation Costs||Med. to High||Med. to High||Low|
|Component Cost||Medium||Low||Med. to High|