Motion control system designers have found a way to eliminate or reduce common sources of position error, such as mechanical backlash, non-linearity, and hysteresis. The method is called direct load position sensing and it employs linear encoders as a source of secondary position feedback. Secondary feedback encoders supplement the indirect position measurement taken by a rotary shaft encoder by measuring the position of the moving load directly.
This method can save money by delivering the specified motion system performance at lower initial cost, and helps maintain system performance over time by getting around the problem of mechanical wear and tear degrading the accuracy of position measurements taken at the motor.
If you’d like to know more, there’s a White Paper available called “Motion Control Primer: Direct load position sensing with secondary feedback encoders”.
Applications for linear feedback sensors are numerous and varied. Likewise, linear feedback sensors are available in numerous form factors and with a wide variety of performance characteristics. Matching your application to the most appropriate sensor can be a daunting proposition.
When choosing the right linear feedback sensor, it is helpful to first define the job the sensor is being tasked to do. One way to do this is to think in terms of the three M’s: (M)easuring, (M)onitoring, and (M)otion control. Linear feedback sensor characteristics that are critical for one of these jobs may not matter as much for another job. We’re going to take a look at each of these jobs and discuss some of the more important linear feedback selection criteria associated with each.
Measuring: In measuring applications, the linear feedback sensor is asked to perform the job of an “electronic ruler”. That is, the sensor is a measuring device used to gauge the size (length, width, thickness, etc.) of the part being produced or processed. Examples of measuring applications include cut-off saws, or any other cut-length applications. In such applications, it is absolutely critical for the feedback sensor to provide 1) high accuracy (low non-linearity), and 2) fine resolution. Other factors, such as a fast update rates and highly rugged enclosures are typically not as important in most measuring applications.
Continue reading “Linear Feedback Sensor Applications: The Three M’s”
Peter Nachtwey of Delta Computer Systems has written an excellent primer on electro-hydraulic motion control. In addition to many design and component selection tips, he highlights the benefits of magnetostrictive linear displacement transducers (MLDT) for position feedback to the controller. Check out the article in the July edition of Design World online, called “A Second Look at Electro-Hydraulic Motion Control Systems.”