In the past, machine builders often made their own linear actuators. They typically assembled, programmed, and troubleshot multiple components from different suppliers, including separate servodrives and control systems. Those performing the mechanical and electrical integration needed experience, performed detailed calculations, and allowed for linear-feedback devices and forces from magnetic attraction when using direct-drive linear motors.
Who, What, Where
Edited by Robert Repas, [email protected]
Rockwell Automation Software, rockwellautomation.com/rockwellsoftware/
Software integration presented additional challenges. Complex application routines and custom configuration of individual components turned programming and debugging into a protracted and painstaking trial-and-error process. The amount of time and effort needed to set up, configure, and commission these devices led many designers to alternative options, such as pneumatic actuators or timing-belt drives, when a linear motor or ball screw would have been the better choice.
Design improvements and the introduction of powerful software tools made building and integrating linear actuators into a machine fast, efficient, and simple. For example, there’s no longer a need to select and configure many different components. Linear actuators now come as completely assembled, integrated units. This reduces reliability problems that crop up when piecing together products from separate manufacturers.
Contributing to this simplicity is the development of a common hardware and software platform that supports multiple control disciplines, such as motion, drives, and discrete components, and both rotary or linear-motor types. Machine builders can now employ a single common-control platform that can deploy the software developed for one application across a variety of controllers within the platform family.
These desktop applications do not develop overnight, but rather take a more evolutionary approach. The current Windows version of the Rockwell Automation Motion Analyzer software first appeared in 1998. It, in turn, was developed from a DOS-based application known as Systex released in 1988. Stepping back even further, the core model of the Systex software was first run in 1980 on a Sharp PC-1211 pocket computer. As processors became more powerful, the software leveraged the added computing punch with new features and advanced capabilities such as motion-analysis and simulation.
Advanced motion-analysis software helps reduce much of the complexity involved with linear-actuator selection. Using a step-by-step fact-gathering process, the software prompts users to input specific information about the application to be considered, along with various cost and performance preferences. The requested information typically includes: the voltage and operating temperature that the actuator will be exposed to; the motion profile; mounting orientation; actuator type to be considered; the amount of payload; and the location of the payload center of gravity.
The Rockwell motioncontrol portfolio
One company that has taken the integration of linear actuators with selection and design software is the Allen-Bradley div. of Rockwell Automation. Their MP-Series of integrated linear stages comes in both ball-screw and direct-drive linear-motor styles. Using Rockwell Software RSLogix 5000 programming software along with the Allen-Bradley Motion Analyzer servosystem selection and optimization software, engineers specify load and motion-profile parameters that selects the appropriate linear stage based purely on desired performance. The software then helps configure the motion-control system to run the stage. The designers do not need to worry about the internal technology or how it interfaces with the control system.
The software then searches for an actuator and drive combination that fits the specified criteria and provides a list of possible options. Users simply select from the list of actuators compatible with the application needs.
Other manufacturers offer sizing software that helps pick an actuator for a given situation, but few offer the breadth of a fully integrated analysis, optimization, simulation, and selection. For example, Motion Analyzer integrates with SolidWorks 3D CAD software to import static inertia data and export motion move profiles to SolidWorks Motion Study.
Most software also lets engineers analyze actuator performance under different scenarios using different types and sizes of stages and drives. This lets them make more-accurate performance and value comparisons to select the actuator they feel is best suited to their needs. Once the actuator choice is entered into the software, the software checks the selected components against machine requirements to make sure the design achieves the desired result.
An integrated approach to linear-actuator selection also helps streamline the commissioning process. For example, the choice of linear stages already integrated into the control system software reduces setup time. Commissioning is as simple as going into the axis setup and selecting the drive and actuator part numbers from a drop-down menu — a much-faster approach than looking up each part number manually from separate vendor data sheets. Softwarebased selection and sizing not only removes much of the complexity, but also makes the decision process much more transparent to the designer.
Beyond sizing and selection, today’s software tools have grown to include optimization, simulation, and performance prediction capabilities. For example, ratio-analysis tools help designers select gearboxes, timing belts, and ball screws optimized to the application. Likewise, analysis tools show where torque produced by the motor is consumed and provide for rapid “what-if ” analysis of needed improvements.
A caveat to observe when using this software is to remember that it is not a mind reader. The software has to know the design data for any mechanism that is analyzed. Unfortunately, this information is not always readily available. For instance, tuning the simulation still requires information about system compliance and backlash. The software calculates and adjusts these parameters behind-the-scenes to give the engineer a virtual plug-and-play experience. Likewise, human expertise is still needed to interpret how to use the results of the analysis. The software can only advise whether or not the proposed mechanism works. It can’t replace the human creative spark that dreams up the idea in the first place.
Improved programming software also helps reduce setup and installation time. Diagnostic tools once used only for rotary motors are now available for linear actuators. These tools help the commissioning engineer get the system up and running quicker then. The engineer no longer needs to worry about offsets, phasing errors, and motor parameters such as pole count, feedback resolution, resistance, and inductance.
As linear-actuator technology continues to advance and software tools become more widely available, the “performance versus complexity” dilemma continues to diminish. With innovation, performance, reliability, and simplicity rolled into a single package, the new breed of linear actuators with design software have all the characteristics of a time-proven, multipurpose automation tool.