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What is a Laser Gauge?

ils80A Laser Gauge is an instrument suitable for outside diameter measurement, featuring

• Contact-less operation
• High Accuracy
• High Speed

 


Working Principle

A transmitting unit emits a laser beam that scans at a very high and known speed across the measuring range.

Every object placed in the measuring field interrupts the laser beam and casts its shadow into the receiver.
By measuring the shadow time, the outside diameter of the part can be exactly computed.

In addition to the diameter measurement, by checking other combinations of light / shadow segments, it is possible to measure any other dimension related to the shadow cast by the part.

Signal processing electronics convert time into diameter and dedicated software packages provide additional features like:

  • diameter display,
  • tolerance checking,
  • part sorting,
  • machine feed-back and process control,
  • statistical analysis and reporting,
  • computer interface

What is an Intelligent Laser Sensor?

ils13 pcAn Intelligent Laser Sensor is a Laser Gauge with built in microprocessor electronics, to process the optical signal in order to get the diameter value without using any additional external electronic unit. All measured data are transmitted in a digital format to external units such as a PC, NC or PLC through a standard RS232/RS485/Ethernet serial line.
The basic sensor software installed into the sensor computes the diameter (or the other dimensions selected) and provides data transmission.
More specific functions, such as machine feed-back, tolerance check or statistical analysis are performed by the User’ s external Electronic Unit equipped with a serial interface and suitable communication driver written by the user. Due to their specific features, the Intelligent Laser Sensors are an ideal component for Machine Manufacturers or O.E.M. (Original Equipment Manufacturer) Customers.

 

The Dedicated Measuring and Control Systems

sistemaIn addition to computing and transmitting the diameter (or any other measurable dimension), the software installed into the sensor can perform more complex functions required by the specific application. Dedicated software displays the diameter, checks the tolerance status and sorts any out of specification part, provides automatic machine regulation, prints statistical reports for Process Control and Quality Certification,
allows the interfacing to external computers and, generally speaking, provides any other performance that is required by the specific application.To provide a suitable interface to the user and to the machine, the intelligent laser sensor can be connected to some external units made by Aeroel, like a Display Module or Operator Interface Panel, etc.

These units have no local “intelligence” and are connected to the sensor through the RS485 serial line: the application software loaded into the sensor drives the external units and sets the overall system functions and performance.

The application software installed into the sensor can be modified / replaced by loading a new package through the Ethernet line: in this way it is possible to guarantee the software correction / up-grading and the remote service

Laser Gauge, Electronic Control Unit and Application Software combine together to build a Dedicated Laser Measuring System, which is suitable to perform complex measuring and control tasks.

How Does It Works?

The AEROEL laser gauges series XLS use a visible Laser Diode as a high intensity, monochromatic light source: a thin beam of this light is then collimated onto the object to be measured. The laser beam is deflected at constant speed by a turning mirror positioned at the focus of a transmitting lens, so as to obtain a parallel-moving scanning beam in the measuring field. During the scanning period, the laser beam intercepts the object being measured and casts its shadow onto the receiver.

The duration of the shadow is proportional to the transversal dimension of the measured object, while the duration of the light is related to the object position in the measuring field. Inside the receiver a lens gathers all the light from the transmitter and concentrates it on a high-speed photo diode. The photodiode signal, after suitable manipulation, is processed by the microprocessor which calculates the edge detection times and takes the measurement of the diameter and the position. Other measurements that are determined by edge detection can also be measured with great precision and in fractions of a second: in whichever case where the edges of one or more shades can represent the dimension to be measured, laser gauges are the ideal solution to the problem of control.

In practice, the instrument consists of a transmitter that contains the laser diode and the optical/mechanical scanning system and a receiver fitted with the detection photodiode and the electronics to process the optical signal. The electronic system inside the gauge consists of 4 boards that are common to all Aeroel gauges (Unica system)

 

schemaBoard 1: supply unit

Board 2: motor and diode laser driver

Board 3
: video signal processing and edge detecting

Board 4
: CPU and communications

 


At board 3 output there are binary signals (impulses) which when transmitted to an Aeroel CE-10 or IBU electronic unit allow the piece diameter and position to be calculated. In this case the signals are processed by the microprocessor in the external electronic unit -: the XLS gauges are thereby compatible with the previous generation ALS gauges to all effects. The signal processing methods and performance of the gauge are determined by the external unit’s EPROM resident software.

Board 4, fitted with its own Flash memory resident software and reprogrammable externally, allows internal processing of the measurements and use of the gauge as a real intelligent sensor : the results of the measurements are transmitted externally by means of Ethernet / Rs232 / Rs485 communication lines. The measurement type and method and the communication protocols essentially depend on the software installed in the gauge and are described in the software manual.

DUAL AXIS WORKING DIAGRAM

The NO-VAR Technology allows the compensation of thermal expansion

The NO-VAR (NO-VARiation) technology developed for the Aeroel Laser Micrometers allows one to simply get perfect diameter measurements, even in non thermally controlled environments, when the ambient temperature is significantly different from the reference temperature (20°C).

Thanks to this new technology it is possible to get in the workshop or in line, the same results that one would get in a controlled temperature metrology room when measuring any material and even when the ambient temperature is changing by some degree/hour.
You will no longer have to be concerned about frequent gauge remastering operations when the room temperature is changing, nor will you have to take into account part expansion.

The problem of thermal expansion

train2

Any measurement process must take account the effect of the ambient temperature which affects both the measuring instrument and the part to be measured. Even if we would have a “perfect” instrument, not affected in any way by the room temperature, we would have to consider the effect of the room temperature on the part’s dimension.
It is well known, for example, that a temperature difference of 10°C will result in a change of 3.6 µm on a 30 mm steel part, since the typical steel thermal expansion coefficient is about +0.012 µm/mm °C. In practice, with this deviation you have to add the gauge’s thermal error, which is generally not known nor is perfectly reproducible. As a result, until now, no one was able to predict with reasonable accuracy the overall measuring error when the instrument is working at a temperature different from the reference temperature (20°C). The only way to by-pass the problem was to proceed to frequent re-mastering operations, using a master made with the same material of the parts being measured and stored near the gauge at the same temperature of the parts to be checked.

How was the NO-VAR technology born?

Since the very beginning the Aeroel laser micrometers have been designed and manufactured to have a negative thermal coefficient of expansion. This value was very close to the steel one but opposite in sign in order to self-compensate the thermal expansion of steel parts. This special feature has made it possible to use the Aeroel micrometers in the workshop or on-line, to accurately measure steel parts, without the need for frequent instrument re-mastering. Nevertheless before today the self compensation effect was not perfect, either because the thermal expansion coefficient of the steel varies from alloy to alloy, or because the gauge thermal coefficient was really not perfectly known and reproducible. In addition it would have been impossible to compensate materials different from steel (i.e. aluminum), as their thermal coefficients do not match.
Nowadays, thanks to the NO-VAR technology, all these problems are eliminated and the Aeroel Laser Micrometers are perfect for use in non-thermally-controlled environments and to measure any material very precisely.

eng graf novar

How has it been possible to achieve this result?

camera 01

Four fundamental elements have enabled us to achieve this important result :
The thermal coefficient of any instrument is perfectly known and reproducible over time and temperature. Using a climatic chamber to perform the tests, the coefficient is measured gauge by gauge and stored in the gauge memory.
The instrument and the room temperature are measured in real time by temperature sensors installed in the gauge.
The thermal coefficient of the part being measured is known and its value is programmed in the gauge memory.
Smart software, installed inside the gauge, compensates the part expansion and the temperature effect on the gauge, in real time and automatically.
Of course, to get accurate results, the part being measured and the gauge itself must be in a quasi-equilibrium condition with the environment and the ambient temperature variation rate is within some degree/hour (typically lower than 3 °C/hr).

The on-line measurements

In case of any temperature difference between the part and the environment, caused for example by the part heating due to the machining, that must be considered separately, i.e. by offsetting the measured value or by changing the programmed nominal value used for the process control. Indeed, even if it would be possible to measure the external temperature of the “warm” part, that would not help in any way: the part expansion is the overall result of the internal temperature distribution, which is impossible to know. However it is very reasonable to suppose that the process heating effect turns into an overall expansion which will be constant if the process parameters are constant as well (part mass and shape, machining speed, lubricant temperature, etc); so that the effect can be compensated by an experimental constant offset.
To find such an offset value is rather simple : just measure the “warm” part immediately after machining and then the same part when it has reached the equilibrium condition with the environment. The difference between these two measurements will be the offset value to be programmed. You do not need a metrology room to perform this operation: the Aeroel micrometers will be installed on-line or used in the workshop and the NO-VAR technology will take care of the ambient temperature changes, which is the temperature of the part before machining.

 

TYPICAL APPLICATIONS


misura 1

D=OUTSIDE DIAMETER

misura 4

D=MULTIPLE WIRE DIAMETER

misura 7

(Dx+Dy)/2=AVERAGE DIAMETER
[Dx+Dy]=OVALITY

misura 10 

Y2-Y1=FILM THICKNESS

misura 2
Y=EDGE POSITION

misura 5

GAP MEASUREMENT

misura 8

Dmax-Dmin=OVALITY



misura 11

LARGE DIAMETER D = L0-L1-L2 

 

misura 3

Y(a)=CAM PROFILE

misura 6

Ymax-Ymin=
RUNOUT

misura 9

POSITION AND GAP



 


  

Measuring Transparent Materials (Glass Logic) 

The separation surfaces between glass and air are opaque and can be detected : the distance between the first and the last edge is the external diameter dimension. A special signal processing software (glass logic) ignores all signal included within these extreme edges. The internal diameter cannot be reliably detected and it is impossible to be measured.

glass 1  glass 2

 


 

The "Blistbuster" Software

The “Blistbuster” software is an Aeroel exclusive data processing algorithm, installed in the dual axis sensors, that can be very useful to check the diameter smoothness of a continuous product (for instance magnet wire) and to detect a very special type of recurrent flaws, commonly called “Blisters”.

blister 01

more details

 


 

Very Difficult or Impossible Applications

rotonditaROUNDNESS

The roundness or triangular shape error is the max. difference between ideal circle and actual cross section profile. The diameter of the ideal circle is impossible to know by rotating the part without fixing a rotation centre.

 

spessoreTHICKNESS

A small misalignment affects the thickness measurement: S' = S cos a + L sin a

For small angles the measured value is: S' = S + L sin a

and the error L sin a can be very large.

 

posizionePOSITION OF A FLAT SURFACE

The position of a flat surface is difficult to be measured with high accuracy, due to complex reflections of the focused laser beam

 

diametro foroHOLE OR DIE DIAMETER

The diameter of a hole (die) is very difficult to be measured, because of the tight alignment required and the reflections in the hole.

The “Blistbuster” Software

The “Blistbuster” software is an Aeroel exclusive data processing algorithm, installed in the dual axis sensors, that can be very useful to check the diameter smoothness of a continuous product (for instance magnet wire) and to detect a very special type of recurrent flaws, commonly called “Blisters”.

What is a “Blister”?

In some manufacturing processes, as i.e. the enameling of copper wire, it’s possible, under given conditions, that on the wire surface a special kind of flaws are produced: these are very similar to small bubbles or holes and they turn into very local diameter changes. In addition, when they appear, they persist on quite long wire sections, until the cause has been removed. Measuring the simple average diameter or even the max and min diameter is not enough to detect and “measure” that type of flaws.

blister 01

How to detect “Blisters” ?

The “Blistbuster” software has been designed to detect and to “measure” such type of flaws, using new and dedicated numerical parameters. Considering the speed of product, the very small dimensions of each flaw, the gauge scanning frequency and the flaw location along the wire circumference, it is absolutely impossible to guarantee that any single flaw is seen and detected.

Nevertheless, by storing into the processor memory a rather high number of single-scan measurements and processing them using a special statistical algorithm, it is possible to determine that some of these has been taken just over a local flaw, as the result of such a scan is very different form the average wire diameter and much higher than the single scan repeatability of the gauge itself. So the diameter deviation of such scans has really to be imputed to the product non-uniformity.

In example, the sketch below shows the “distribution” of the measurements taken on a moving wire, having small and recurrent flaws: in addition to the main Gaussian distribution (which is typical of the gauge) an additional “spurious” distribution can be seen, that is due to the blisters.

blister 02

The Output Data

The Blistbuster software processes K x N scans (or single measurements, couples of X & Y values) and computes 3 new parameters:

  • PDF = Percentage of “faulty” scans over the total number  K x N
  • ADF = Average flaw height, expressed as Diameter Change and always in MICRONS INTEGERS, no matter of the pre-set measuring resolution and units.
  • IDF = Flaw Index, overall parameter given by the product  20 x ADF x PDF / DFSCAL

The parameters to adjust

In addition to the overall sampling time, set by K and N factors, the user can set:

  • the DFSCAL code or the system sensitivity, to attenuate the IDF value dividing it by 1 or 10 or 100, in order to reduce its variation range;
  • the DFSENS code or the flaw detection threshold, , to be always programmed much higher than the gauge single scan repeatability. That is expressed as Diameter Change and always in Millimeters, no matter of the pre-set measuring resolution and units.

Important comments

Please notice that :

  • The Blistbuster function is active ONLY when the product K x N is greater or equal than 200, to have a reasonably high number of data to process.
  • It is strongly recommended to use high scan frequency sensors, to improve the measuring repeatability.
  • The Blistbuster function is based on statistical assumptions: a quite long section of wire must be checked, including a rather high number of flaws.
  • It is absolutely impossible to detect any single scan or to measure its real dimensions.
  • As it is impossible to know and measure the true geometry and dimensions of the flaws, the computed parameters are not directly related to the true dimensions and to the quantity of flaws, but they can be used as “process indicators” related to the wire quality and they can be very helpful to monitor the process and to prevent from manufacturing defective product.

Logo UeLogo MinisteroFriuli venezia GiluliaFonfo SviluppoProgetto cofinanziato con il Fondo Europeo di Sviluppo Regionale del Programma Operativo Regionale del Friuli Venezia Giulia Obiettivo "Competitività Regionale e Occupazione" programmazione 2007/2013