What is a Linear Scale?
Alliance calibration specializes in ensuring accuracy where it’s most needed, like in precision tools. The linear scale is one of many items that we work on. With a unique design for reading the measurements of motion and position, the linear scale promises accuracy in your machine tools, as long as the linear scale is properly calibrated.
Most modern linear scales are digital and come with an LCD display that shows a clear and exact read. Linear scales provide a very specific service. These measurement tools offer a clear read on the distance between two points by reading the motion along the path of the scale. In this way, linear scales can provide the exact dimensions of workpieces so that they can be worked on properly. By obtaining and maintaining the exact measurement with a linear scale, one can ensure that the workpiece sits properly in a machine tool, which ensures accuracy in manufacturing.
Obviously, linear scales are essential for success involving workpieces and machine tools, because without the right measurement, you can’t get the right fit. And, without the right fit, you won’t have a successful outcome with the workpiece. In order to avoid wasting materials, time, energy, and money, it’s important to have a well-calibrated linear scale on hand for use of machine tools like power saws, turning machines, and milling machines.
What a linear Scale looks like
Linear scales vary in shape and design depending on the brand, but each linear scale shares the same overall structure. The scale is made up of a long, straight piece, similar to a ruler but sometimes thinner. At each end of the beam, there is a mounting bracket. These pieces make it easy to install the scale for a steady and accurate read each time.
In the middle of the beam, the linear scale features a piece called the transducer. The transducer is part of the linear encoder, which is the piece of the scale that reads the measurements and gives you those measurements on the digital LCD display. The linear encoder moves along the scale, and as it does so it reads the measurements and translates them into the numerical display. On many linear scales, the LCD display is attached directly to the encoder on the bracket, but some scales have a wire connecting the display to the encoder. Models like these make the measurement easier to read when the scale needs to be used in a tight space.
How a Linear Scale Works
There are actually two types of encoders: linear encoders and rotary encoders. The linear encoders — which we’ll focus on here — read movements along the path of the straight scale. Rotary encoders are used to measure the movements in a rotation. Rotary and linear encoders are similar in how they function but are designed to interpret different movements.
In order to read the motion along the path of the scale, a linear scale uses a transducer to measure the distance between point A and point B. The transducer travels along a rod or cable that sits between the transducer and the object being measured. As it does so, the encoder sends an electrical output signal that is linear to the movement of the object. The scale uses the change in distance to determine the position of the object.
When the encoder reads the distance traveled, it translates the linear motion into a digital signal which shows measurements like speed, angle, or position. By measuring the moving parts, the linear scale allows you to control the motions of an operating device to get reliable accuracy. This type of exact control is often used in equipment like milling machines or printers.
Absolute vs incremental Linear Scales
There are two sub-categories for both linear and rotary encoders. Each can be either incremental or absolute, and each of those can use one of several possible electromechanical technologies to gather the measurements.
When you’re looking for a linear scale with the most reliable accuracy in any condition, you’ll want to choose one with an absolute encoder. An absolute linear scale measures the exact position by reading a unique pattern on the scale. The pattern varies along the entire scale, so that the encoder can detect exactly where it is along the scale at any time. This means that, should the machine lose power, the encoder will still know the absolute position because of the unique code along the scale.
Absolute linear scales are chosen for their high accuracy and reliable reads, and are necessary for any circumstance that prioritize total certainty, like machines that contribute to safety and protection.
The alternative incremental linear scale offers slightly less reliability, simply because it cannot offer the absolute position should the machine lose power. Instead of reading measurements from a unique code along the scale, the incremental linear scale detects motion by change in position over a period of time. The incremental encoder starts its measurement count at zero the moment that it’s turned on, and completes its count at the full distance. In order to use an incremental linear scale, you need to have a reference point because the measurement always starts at zero.
Common types of Linear Scale technologies
As mentioned above, the variance in available linear scales expands beyond brand and absolute or incremental. Different scales rely on different electromechanical technologies for reading the measurements.
One of the most popular technologies for linear scales is an optical system. In this type of scale, the encoder reads the position, direction, and/or velocity by reading pulses of light with a photo sensor. The light gets sent through windows arranged in the order of the scale. These are the most accurate of linear encoders and are used often in industrial automation.
Another common type of linear scale will have the magnetic linear encoder. These tools have a magnetic scale which gets read by a piece called a read head. The read head detects a change in the magnetic field of the scale, which alternates north and south poles at specific measurements.
Phil Wiseman is Chief Marketing Officer at Alliance Calibration. He earned a B.S. in Chemical Physics from Centre College. Phil is an ASQ Certified Quality Auditor and ASQ Certified Manager of Quality/Organizational Excellence.