Modern industrial machines rely on fast, accurate motion control in order to achieve high product quality and productivity, as measurement errors can lead to increased scrap and production downtime. However, these and other costly headaches can be avoided by choosing the proper position-sensing device for your application.
Although there are a number of position sensing devices to choose from – ranging from potentiometers and discrete switches to continuous feedback devices–the quality, precision, and inherent limitations of each device vary. For instance, potentiometers, being contact measurement devices, are highly susceptible to wear, which can tend to lower the overall performance of a machine. Additionally, signal transmission by means of sliding contacts limits a potentiometer’s average lifetime to 100 million movements, which can be reached in a relatively short period of time; especially in machines with short cycles. Furthermore, potentiometers are single-position measurement tools, meaning that a separate device is required for each measurement, which not only requires the use of additional space, but increases cost as well. Therefore, although a prevalent position sensing device, potentiometers and other contact sensing devices may not be the ideal measurement solution for all industrial machinery applications. Subsequently, choosing the proper device depends largely on the application requirements regarding measurement performance, mechanical package (e.g. mounting), electrical interface, and environment.
In machines where precision, fast cycle times, and quick setup are critical to the machine’s value proposition, magnetostrictive linear-position sensors are quickly replacing other technologies. Magnetostrictive linear-position sensors utilize non-contact, non-wearing measurement technology, which makes them extremely reliable and nearly maintenance-free, significantly reducing the potential for operational errors and machine downtime. Able to provide absolute position accuracy down to 20 microns and measurement cycles as fast as 100 microseconds, magnetostrictive linear-position sensors improve the overall system performance on numerous types of industrial machinery, including many of those utilized within the wood, steel, and plastic industries.
Choosing a robust sensor technology like magnetostrictive sensors, combined with a mounting approach designed to mitigate shock and vibration, can eliminate performance and productivity issues related to sensor failure. Due to their enclosed, non-contact design, magnetostrictive sensors are highly reliable, even in harsh environments; insensitive to contamination; and able to withstand and provide stable and accurate output despite being subjected to vibration and shock – in some models up to 30 g and 100 g, respectively.
Other machine performance issues can be avoided by selecting a sensor with proper grounding and shielding. For instance, some magnetostrictive sensors offer double shielding, as well as isolation of the internal electronics for improved electromagnetic interference (EMI) protection. Advanced LED diagnostics also provide a useful tool for troubleshooting performance issues by providing feedback on magnet and communications operations, which can reduce the downtime required to solve any performance problems that may arise.
Spanning a wide range of price points, magnetostrictive sensors are available with a variety of optional features, including diagnostics and programmability options, stroke lengths ranging from approximately 50 mm (2 in.) to 7620 mm (300 in.), and outputs including SSI, EtherCAT, Powerlink, Profibus, Devicenet, CANbus, start/stop, PWM, and analog. Regarding accuracy, some magnetostrictive linear-position sensors feature non-linearity less than ± 0.01% of full stroke with a repeatability of ±0.001%. Additionally, some magnetostrictive position sensors offer a multiple magnet capability, which can reduce the number of sensors required per machine by combining measurement parameters along a single axis into a single sensor.
Able to deliver high-performance in multi-position sensing applications with as many as 20 magnet positions monitored by a single sensor, magnetostrictive sensors can provide greater cost savings, performance, packaging flexibility, and higher speed for control systems. Multiple tool, platen, or cartridge positions from a single sensor translate to a lower per-tool cost of feedback, and automatic tool or cartridge positioning significantly reduces changeover time, which allows for a higher number of setups, and therefore greater machine productivity. Magnetostriction also provides the increasingly accurate measurements required of high performance control systems, with a linearity correction option to achieve ±20 microns or better and 1 micron resolution; all while maintaining a high resistance to shock and vibration, ultimately resulting in higher quality with less waste. Additionally, the variety of stroke lengths and flexible housing options available simplify shipping and installation. Faster response times via industrial Ethernet protocols, such as EtherCAT and Powerlink, enable tighter control loops, improving machine cycle times and reducing material scrap.
Because they provide high-accuracy, dynamic position measurement along multiple motion axes, reduce cycle times, increase productivity, and improve product quality, magnetostrictive linearposition sensors ensure smooth sensor operation without maintenance expenses and downtime, making them the most reliable and cost-effective position measurement solutions for the complete lifecycle of modern industrial machinery.
This article was written by Matt Hankinson, Technical Marketing Manager, MTS Systems Corporation Sensors Division, Cary, NC. For more information, please contact Mr. Hankinson at 800-633-7609, e-mail him at: