Acuity AR700 Laser Distance Gauges

Description

Acuity introduces the AR700 series of laser distance gauges for measuring displacement and object dimensions. Built on a decade of success with the AR600 laser displacement sensor, industry users demanded faster and more accurate non-contact metrology equipment. The AccuRange 700 boasts output speeds to 9400 Hz and resolutions (model dependent) as low as one sixth of a micrometer. The unit is very compact, measuring approximately 1 x 2 x 3″ (25 x 50 x 75 mm), almost 80% smaller than its AR600 predecessor.

Speed

This Acuity digital sensor has selectable speeds up to 9400 Hz (when using 3-Byte Binary Data format). Don’t be fooled by competitor’s claims of higher speeds. Acuity laser distance sensors are unique and our specifications are straightforward. The device will in fact output 9400 distance readings in a single second. This is unlike our competitors who often quote the maximum sampling rate of their detector. This number is not real because the user will never see data output rates that high through serial or analog interfaces or the cumbersome controllers that are required to operate their sensor heads.

A special Trigger Mode permits users to initiate sampling via serial command or discrete hardware triggers. This trigger can be used for synchronizing multiple sensors. The maximum speed using the hardware trigger is reduced to 4500 Hz.

Resolution

Optics and digital detectors have improved greatly over time and Acuity’s AR700 laser distance sensor offers a three-fold improvement of resolution over its previous model. Resolution is the smallest increment of distance that can be detected by the distance gauge. AR700 sensors specify a 0.005% (of the measurement span) resolution for all models in this series. Resolutions are measured on targets of 85% diffuse reflectance (white) and in static conditions.

Compact size

Measuring approximately under 8 cubic inches, this unit is ultra compact because it houses all electronics for measuring. No external controller or amplifier needed. Each sensor includes the sensor head and 6 feet (2 m) of cable. Note that longer-range sensors have longer mechanical enclosures.

Theory of Operations:

The Acuity AR700 laser distance sensor employs triangulation measurement principles whereby it projects a beam of visible (or optionally, infrared) laser light that creates a spot on a target surface. Reflected light from the surface is viewed from an angle by a digital CMOS line scan camera inside the AR700 sensor. The target’s displacement is computed from the image pixel data.

The AccuRange 700 series includes thirteen measurement ranges from 1/8th inch to 50 inches (3.2 mm to 1.3 m). The linearity specification is among the best in the industry, +/-0.03% of the sensor’s measuring span.

This distance sensor, similar to the AR200 is standard with a variety of serial and analog outputs. On either RS232 or RS422, data formats include ASCII English, metric, native and two binary outputs. The sensor can output error codes for: Target too near, Target too far, Target not seen and Laser off. Analog outputs include a 4-20 mA current loop, 0-10V outputs and two NPN sinking limit switches. All parameters and settings are selectable from pushbuttons on the sensor or through PC serial commands.

Product Applications:

The AR700 is Acuity’s newest digital triangulation sensor. It’s high resolution and fast sampling speeds make it a versatile sensor for many industrial and research applications. As Acuity phases-out the older AR600, the AR700 series will replace it in nearly all applications that demand high-accuracy triangulation sensors.

Road Profiling:

Measuring road surfaces at highway speeds is an emerging application for civil engineers. Pavement engineers demand high signal to noise for non-contact profilers. The high-speed, digital laser sensors from Acuity meet the demands of this field.

Road surface profiling is an important part of highway and pavement engineering. Systems have been developed to collect real-time continuous highway-speed measurements of longitudinal profiles of road surfaces. From this data, engineers calculate International Roughness Index (IRI) or Ride Number (RN). Both of these numbers are expressions for the roughness (and therefore ride comfort) of a road surface.

Road profiling systems incorporate non-contact laser sensors to measure to the road surface and accelerometers to compensate for the effects of the vehicles movement. There are specialized road profiling systems for transverse profile, rut depth, macro texture and other shape characteristics. Profiling has become a crucial practice for transportation departments throughout the world. Road builders, contractors and even US State DOT’s (Departments of Transportation) are responsible for gathering statistical information on road surfaces including the longitudinal profile, mactrotextures, microtextures and roughness to determine coefficients of friction. The measuring tasks are especially challenging for most lasers because road surfaces present many dynamically-changing targets including tarmac, concrete, yellow striping, white striping, etc. Acuity developed special lasers to maintain a consistent sampling rate over varying targets. Acuity has worked with developers of road profiling equipment to produce versions of the AR700 laser distance gauge for use as primary sensors for inertial profilers meeting ASTM Class 1 standards. The result is an AR700 with optics, electronics, and signal processing algorithms specifically for road profiling. Optics, electronics, and signal processing algorithms have been optimized for profiling. The AR700’s 9.4 KHz sampling speed and low-noise digital output makes it the standard for road profiling applications. The result is an extremely accurate, cost-effective sensor for all surface types, vehicle speeds, and vibration, sunlight, and temperature conditions encountered in profilometry applications. Acuity has deployed over 100 laser sensors for road profiling worldwide.

Lumber Measurement:

Acuity sensors are used to measure and verify the dimensions of logs and cut lumber. The digital CMOS technology performs well on dark and light colors.

Steel Measurements:

Steel castings require the measurement of hot, radiating material. This is best performed with non-contact laser sensors. The Acuity sensors excel at this application when equipped with a high-power infrared laser and a narrow band pass filter.

The steel industry demands accurate measuring equipment to be used under difficult circumstances.

The environment is harsh, with high dust content and hot temperatures. The targets, hot metal, can be especially difficult because they radiate glowing light at elevated temperatures. Acuity’s AR700 series is especially designed to measure to glowing targets. Most sensors used within this industry are equipped with the AR600’s optional filter and high power laser option. Dimensions are captured with either single or multiple sensors. Thickness measurements are achieved with the use of two opposing sensors and a standard, PC computer. The sensors are often protected behind insulating glass or within a protective enclosure. Acuity offers customized enclosures for the AR600 sensors through Sequence Technologies, a measurement and controls company serving the steel industry. These enclosures can be either air or water cooled so that the sensor can be placed close to hot surface targets.

Rubber Thickness Measurements:

The AR700-4 (formerly AR600-4) with a 5 mW laser diode is selected by an international reinforced rubber conveyor belt manufacturer to replace existing methods. Acuity sensors perform accurately on black, shiny rubber surfaces.

Acuity laser sensors are used widely throughout the rubber manufacturing industry. Rubber sheet manufacturers need online sheet thickness measurements for Quality Control and system control feedback loops. Rubber presents several challenges for metrology equipment, including the extremely low surface reflectivity, the dirty measuring environment and the temperature of the material to be measured. Manufacturers demand reliable, non-contact measuring devices to minimize downtime and scrap material production.

A large international rubber conveyor belt manufacturer uses Acuity AR700 laser displacement sensors  to measure the thickness of black rubber sheet in a calendering process. After a one-month trial period, the AccuRange 600-4 sensor model (now using AR700-4) was chosen to replace other equipment which failed to meet accuracy requirements. The AR600 sensor is extremely durable and met the environmental requirements for this industrial application.

During calendering and rubber processing, the surface of the rubber sheet is very shiny and very black, creating conditions where little light can be reflected. These are often the most challenging conditions for optical measurement sensor. Acuity installed an upgraded laser diode in the AR600-4, bringing 5 mW of laser power (standard is 1 mW) to get a stronger return signal off the dark surface. The result was excellent sensitivity on the rubber sheet and fast measurement speeds.

This rubber manufacturer monitors the thickness measurements using four sensors positioned at the top, 140 mm (5.5 in.) from the sheet surface. The rubber sheet lays across a roll cylinder. The top of the roller is the reference (zero) surface for thickness measurements. The laser spots aim directly perpendicular to the sheet surface at four different points across the sheet width for this process where the material stretches between two rollers, so that the roller gap can be adjusted accordingly to produce the desired (consistent) sheet thickness.

Concrete Block Height Measurements:

Popular architectural pavers are manufactured using a vibrating press. The product is produced on steel pallets. These pallets pass beneath a height measurement system using Acuity laser displacement sensors.

Manufactured archtectural pavers and wall blocks are growing in demand because they last longer than site= poured concrete and because they offer fantastic choices of color, shape and texture. Furthermore, concrete pavers are relatively simple to install and do not require a mason’s training. A United States integrator who has for years been making equipment for the concrete block industry, is addressing a quality asurance issue by integrating Acuity laser displacement sensors into a non-contact height measurement system. Using AR600 sensors, the system measures the height of molded concrete blocks as a conveyor passes them beneath a measurement archway. The measurement environment is industrial in nature and the integrator took measures to block airborurne dust from collecting on the sensitive optics of the laser sensor. The product, called the “Blockqualifier”, is placed in service downstream from the block casting machine. Uncured bricks are placed on a steel palette which is conveyed beneath the archway of the Block Qualifier system. As it passes beneath, the AR700 sensors gage the height profile of the blocks. This information is displayed on an operator’s screen and processed in software algorithms to determine if they are within dimensional specification.

Package Dimensioning:

 
Large distribution center use laser systems to measure the dimensions of cardboard boxes traveling down a conveyor. The AR600 laser sensor accurately measures these dimensions which are later verified against known dimensions stored in the parcel’s bar code.

Thickness Measurements:

 
Two opposing lasers measure to two sides of a target to report the target’s thickness. The benefits of using lasers include high accuracy and non-contact measuring.

One of the most commonly-requested applications is thickness measurement using two, opposing laser displacement sensors. The basic premise for this applicaiton is to aim sensors at the two sides of an object. If you know the readings of laser A and laser B and the fixed separation distance between the laser sensors, one can easily determine the thickness of an object. One must take important considerations to make sure that the laser is aimed perpendiculary to the surface. If the target material is moving, such as with continually-cased metals, it is necessary to synchronize the laser sensors so that they take distance samples at exactly the same time.

The following picture depicts a thickness measurement application where Laser-view Technologies integrated a complete hardware and software solution for a components manufacturer. The manufacturer was producing plates of various contours and was currently measuring its thickness with manual callipers. Laser-vew was hired to make a semi-automated measuring statioin using non-contact laser measuring sensors. They chose two AR600 series sensors because of their superb accuracy and simple RS232 interfacing. Today, Acuity suggests using AR700 sensors as upgraded replacements to the AR600 series.

Plywood Sheet Thickness Gaging:

 
Sawmills are harsh environments that demand accurate laser sensors under dusty conditions.

Production of plywood and OSB (oriented strand board) sheet is highly automated. Several Acuity customers are system integrators who develop specialized instruments for the forest products industry.

One machine builder develops digital instruments for thickness measurement of composites, honeycomb sandwiches, composite wood, concrete and other pultruded materials. He chooses AR600 laser dsiplacement sensors in opposing pairs to dimension wood sheets in several locations. The AR700 with a CMOS detector array performs well on plywood, despite the presence of dark-colored knots. Their systems also employ ceramic piezo transducers for defect recognition on their blow detector system. Thickness gauging is important becasue thin boards are inferior and sheets that are too thick waste materials and resources.

Sawmills and plywood manufacturing plants present special challenges becasue they are dusty environments. All sensor equipment is kept clean using forced air. Air nozzles blow pressurized air across the optical windows to prevent buildup of dust that could diminish the accuracy of measurements.