Linear Digital Measuring Device


Specialty Motions, Inc. has developed a simple but elegant method for measuring long-length materials such as linear shafting, carbon fiber tubing, wire cables or long sheets of wood, metal, cording or plastic in a variety of diameters and shapes. In its standard form, the Linear Digital Measuring Device (LDMD) is designed to measure materials, in any increment, up to lengths of 465” and is consistently accurate to within .003” at 12’. Utilizing the easy to read Digital Readout the LDMD is extremely easy to use and versatile. A durable and rugged precision measuring tool, the LDMD operates on a highly efficient linear recirculating ball bushing bearing arrangement, where straight-line travel as well as pitch, roll and yaw are kept to a minimum to ensure accuracy within .003”. This digital measuring tool operates in much the same way as a machinist digital caliper. The LDMD can be zeroed by sliding the carriage to the “home” position and touching a button on the digital readout (DRO). The unit is now set at zero. To measure, slide the carriage away from “home” to allow the work piece into position, then return the carriage, allowing the unique articulating tooling arm feature to make contact with the end of the work piece. 

The DRO gives you a length dimension in large, easy-to-read numbers to the fourth decimal place, much like a very large caliper that has machine-tool accuracy. The DRO can be switched on the fly to display in inches or millimeters. It is capable of absolute and/or incremental readings, allows for an offset for end-of-arm tooling adjustments and has linear and segmented error compensation capabilities. The DRO uses an RS232 connection method for data acquisition and remote PC features and printing. The DRO is expandable to accommodate multiple axes of motion, if desired, such as to automate the optional MDS stand or rolling table. “We took our knowledge of linear motion and combined it with our knowledge of encoding and created a machine-tool quality measuring device,” said Tom Corey, SMI President. “The Linear Digital Measuring Device came from our own need to precisely measure long lengths easily, quickly and accurately on the shop floor, under harsh and varying conditions. After looking at the market and finding nothing to meet our demanding needs, we created the LDMD to be easy to use, adaptable, rugged and reliable.” The patent-pending LDMD is constructed using a proprietary extrusion for rigidity and consistent thermal expansion properties. Simple mounting options allow it to be used horizontally, vertically or laterally and can operate at high traverse speeds up to six feet per second without skipping count. The IP67-rated encoder is fully submersible, shock-resistant and can be used in harsh environments. 

The linear encoder is also designed to minimize the effects of thermal expansion and will grow linearly along with the extrusion to minimize twisting, bowing and distorting of other scales and systems. The robust carriage and rail arrangement make it very durable and adaptable. With no contact or wear items, LED’s or glass scales to break or burn out, the linear encoder requires no cleaning or maintenance and offers a long life. An unlikely out-of-adjustment condition can be quickly resolved using gauge standards and/or laser positioning and adding error compensation adjustments.  Each linear encoder is serialized, and SMI offers traceability to ISO 10012-1 offering machine-tool quality results. Highly versatile, the LDMD comes with a unique quick-change tooling arrangement featuring precision end plates and tooling pin locators. As well, optional articulating tooling arms, V-block adapters and custom tooling are available. The LDMD can also be mounted an optional rolling table or stand to allow for quick and easy setup from job to job.  The stand can be automated with lift tables and foot-pedal controls, allowing adaptability for large- and small-diameter work pieces.


  • measure long-length materials
  • accurate to within .003” at 12’
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