As linear motion systems continue to advance, new solutions are emerging that enable both system designers and end users to realize benefits such as simplified assemblies, greater precision, and zero maintenance. One such solution is the integrated measuring system (IMS), which has demonstrated notable cost savings and improved design efficiencies in linear motion automation applications.
To fully benefit from this solution, it is essential to understand how the IMS works and keep in mind key considerations when working with it.
An IMS uses the inductive measuring principle to place the linear encoder inside the linear guide rail so that both guiding and measuring functions can be achieved with one component. This configuration replaces traditional designs that relied on separate external linear encoders and readers that were susceptible to dirt and lubricant contamination and breakdown. The new design not only solves the contamination issue but also improves the precision and uptime of linear motion systems and eliminates maintenance altogether.
Consider a task within the automation industry that requires placement or positioning of a workpiece using a linear motion axis. The basic components needed to perform this task include a servo controller, a servo motor with a rotary encoder and a linear motion axis such as a ball screw.
Traditionally, this type of system would be designed using a semi-closed control loop in which the required workpiece position is communicated from the PLC or CNC to the servo drive. The servo drive directs the rotation of the servo motor, and an externally mounted rotary encoder precisely counts the turns using the joints of the ball screw and the corresponding lead to position the workpiece accordingly on the linear motion axis. The downside of the semi-closed control loop is that it indirectly measures the position of the workpiece, thereby increasing the opportunity for mechanical drive chain or belt positioning deviation and decreasing precision.
Alternatively, an IMS allows system designers to switch to closed-loop control to overcome position errors and improve precision. In a closed-loop configuration, the linear encoder is mounted in parallel to the linear guideway to measure the actual position of the workpiece. If there is a difference between the actual position and the required position, the servo drive corrects any position error; therefore, this approach removes error from the drive chain or belt.
These systems are currently available using inductive measuring and magnetic measuring principles. Compact models for magnetic measuring offer robust performance and economy for applications that include automatic positioning, handling, and axes with linear motors. Larger systems for inductive measuring are also exceptionally robust and deliver greater precision for applications such as machine tools.
Benefits of IMS
System designers and end users want linear motion solutions that are easy to assemble and keep components to a minimum. Consolidating two functions — measuring and guiding — into one component offers many benefits, including faster commissioning, lower design costs and less maintenance.
From a performance perspective, integrated measuring systems can measure position at speeds up to 5 m/s, which is ideal for high-speed applications, for example, when using linear motors. Machine designers also want solutions that are compact to save space for other added functionality or to reduce the overall size of an assembly or piece of equipment. Some companies offer compact IMS models for ball rail systems in sizes 15, 20, and 25. For inductive measuring systems, integrated measuring is available for sizes 20 to 45 for ball rail systems and sizes 35 to 65 for roller rails.
Another benefit of integrated measuring systems is EMC shielding, which is particularly beneficial in harsh environments with magnetic fields or electrostatic discharge. Sensors reside inside a metal housing or, in compact models, inside the steel body of the runner block. Both locations function like a Faraday cage, protecting the encoder from disturbances.
Integrated measuring systems check off all these boxes while also improving precision and eliminating waste and maintenance costs for the end user. These measuring systems address many issues that arise from using optical position sensors (glass scales), including exposed linear encoders that are susceptible to dirt, or limited speed if the glass scales are part of a sealed linear encoder system.
Improving Linear Motion Precision and Uptime
To better understand the benefits of using an IMS, let’s look at the machining industry. By placing the encoder in parallel with the linear guide rail, the actual position of a workpiece is recorded instead of an indirect measurement, resulting in increased precision and more uptime. The closed-loop control enables correction of positioning errors and greater placement precision before machining begins, resulting in little or no start-up waste (re: uptime), fewer production defects, and overall higher quality parts.
Also, the IMS does not require the high level of maintenance or frequent replacement costs commonly associated with an external encoder component. Eliminating the external encoder effectively eliminates the opportunity for dust, shavings, or other particles to enter the motion process and disrupt the function and accuracy of the system.
To increase the accuracy and uptime of linear motion systems for its machine tools and metal machining equipment, one manufacturing company decided to forgo optical position sensors and use integrated measuring systems in all the new and upgraded machine tools at its plant. After more than two years of testing, the new system has demonstrated savings of tens of thousands of dollars, which has been measured in both reduced maintenance costs and increased machine uptime.
Previously, the manufacturer had relied on optical position sensors for its metal cutting manufacturing equipment that included profilers, surface grinders, and drills. These sensors produced the required height accuracy, but they were extremely expensive over long distances, had continual maintenance costs and frequently caused unexpected machine downtime.
By adding integrated measuring systems into the linear guides of new and upgraded equipment, motion systems were able to detect the absolute position of an axis down to +/-3 μm/m. And since the motion systems use induction measurement, they are now wear-free and require no maintenance.
The integration of sensor technology and onboard electronics in the ball and roller runner blocks also meant design engineers could avoid external measuring systems and sealing air systems, which saved both cost and installation space. Even in areas where metalworking fluids, dust, and shavings are present, the new system does not require high-maintenance air sealing systems, and electrical and magnetic interference do not affect performance.
Selection Considerations for IMS
When it comes to selecting a supplier for IMS for linear motion, it’s best to choose a reputable company that has relevant experience and expertise in your industry. A knowledgeable supplier will listen to your needs and invest in understanding your process to help you design the best solution to solve a problem or achieve a goal.
To ensure the long-term success of your system and simplify tasks such as system maintenance, part replacement, and future expansion, it also helps to seek a supplier that offers a complete automation portfolio, especially from a mechatronics perspective, providing drives, control, and mechanical components. This will make it easier to seamlessly integrate with other machine control and factory automation solutions.
This article was written by Jonathan Richards, Product Manager, Linear Guides, Bosch Rexroth Corp (Bethlehem, PA). For more information, visit here .