Enabling High-Precision, High-Reliability Sensors for Industrial Automation

Herbert Chelner, CEO and Chief Scientist

Dr. Robert A. Mueller, President and General Manager

Abstract

Micron Instruments has been the leading manufacturer of semiconductor strain gages (SSGs) for over 30 years. Micron’s SSGs serve as a critical component in precision nano-meter microscopy products; implanted medical devices for cardio, neurological, and spinal patients; prosthetic devices for amputees; structural measurement devices; load cells; both extreme low temperature (deep space applications) and high temperature (industrial boilers); advanced power devices for space exploration; aerodynamic test and measurement; and rocket motor monitoring for safety and condition-based maintenance.

That said, Micron’s largest and fastest growing market segment is Industrial Automation and Robotics. In this paper, we’ll overview SSGs and then present video clips from several of our key customers on how SSGs enable the high precision and repeat-ability required for the advanced force torque sensors driving the robotics explosion.

Semiconductor Strain Gages

Semiconductor strain gages were discovered during the transistor era and became commercially available early in the 1950's. These gages may be homogeneous or diffused. Diffused gages have a variety of problems that limits useful life and affects performance.  There are two main elements from which semiconductor gages are made. These elements are Geranium and Silicon and they can be P or N doped. At Micron Instruments, the P doped (Boron) Silicon gage is selected for the basic strain sensor, and the N doped Silicon is used for the temperature sensor. Silicon gages have been proven to be more stable and more corrosion resistant than Geranium gages.

The Micron Instruments Miniature P-doped Silicon Semiconductor Strain Gage

Micron’s strain gage is manufactured from a Boron Doped Silicon ingot grown as a single crystal. The strain gage crystalline axis used is where the longitudinal over the transverse ratio is maximized. The reverse is true for the Silicon temperature sensor. This means that the finished gages will be unidirectional and transverse strains will have no significant effect on performance when properly manufactured.

Gage shape is application sensitive. Semiconductor strain gages are normally bar shaped; the length and resistivity varies but the width is nominally 0.005 inches[1] and the thickness 0.0005 inches for a bar gage.  Normally, a gold lead is bonded to ends of the gage for electrical connection. For miniature sensors, it can be important that the gold electrical leads come out the same end, requiring U shaped gages. The U shaped gage also has twice the resistance over the same length, making it desirable for small areas of high strain or for wireless applications where higher resistances are important. There are also M shaped gages, which provide four times the resistance of the same length bar gage when even higher resistance is required.

Force Torque Sensors for Industrial Automation

Most robotic applications require a multi-axis or 6-axis force torque sensor to give feedback to the robot. This gives the robot a sense of “feel”. The 6 axis configuration allows force to be measured and controlled in three dimensions and two directions. The force from each axis is measured using strain gages, typically organized into a Wheatstone bridge.


The video below, courtesy of industry leader ATI Industrial Automation, illustrates the critical role played by Micron’s semiconductor strain gages:

            Click Here to View the ATI Video

Enabling the World’s Most Advanced Robots

Force torque sensors built from Micron’s SSGs were also used in NASA/JPL’s RoboSimian. RoboSimian uses its four general purpose limbs and hands, capable of both mobility and manipulation, to achieve passively stable stances; establish multi-point anchored connections to supports such as ladders, railings, and stair treads; and brace itself during forceful manipulation operations. The video below shows Robosimian performing in the 2015 DARPA Robotics Challenge Finals Competition:

 Click Here to View RoboSimian Video

 Digital Strain Signal Conditioners

Micron Instruments’ SSGs deliver a typical full-scale output of 20mV/V when temperature compensated. The SSG output signals that must be “conditioned” to produce usable numbers. A digital strain signal conditioner is a good choice for this task.

Micron Instruments has already worked with innovative companies on optimal selection, placement, and processing of semiconductor strain gages for high frequency, high pressure, and high-temperature applications. If you’d like to discuss your application or design, please contact us for a free, confidential consultation either by email using our Contact Us Form or phone (805-522-4676).

[1] All dimensions herein shall be in inches, unless specified otherwise.
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