A Key to Successful Production-Integrated Measuring – the Encoder

By Reinhard Kuhn
HEIDENHAIN, Traunreut
Product Manager

An encoder’s coefficient of expansion and its tolerances will play a more significant role in future ISO standards for classifying coordinate measuring machines.

A measuring room offers optimum conditions for precise measurements. But it has several disadvantages including high costs for the room, the machine and temperature stabilization, as well as interruption in the flow of production.

Customers continue to push to install more control over the manufacturing process. Part of this push involves placing the measuring machine spatially closer to actual production, a modification known as production-integrated measurement. Through such a modification, measurement results can go “online” into the control of production and thereby affect the precision of the manufacturing process.

However, the harsh nature of a typical manufacturing environment places new requirements on measuring machines. These requirements either did not exist or were less critical in the sheltered surroundings of a measuring room.

Measuring machines on the shop floor are exposed to changing temperatures and more difficult ambient conditions. Shock, vibrations, and contamination occur often. Manufacturers of measuring machines are responding to these requirements with various designs and approaches. However, all are in agreement on one point: Deviations from the 20° C reference temperature specified in DIN 102 change the length and angle on both the work piece and the measuring machine, and these changes must be mathematically compensated.

KNOWN BEHAVIOR
The defined, reproducible thermal behavior of the encoder is indispensible for accounting for such deviations. The encoder’s coefficient of expansion and its tolerances will play a more significant role in future ISO standards for classifying coordinate measuring machines (see ISO TC 213-WG 10).

Thermal expansion = change of length – an unknown quantity

The coefficient of expansion, or deviations from it, influence the use of encoders on measuring machines. Encoders usually feature measuring standards of steel, glass, or glass ceramic.

The relevant literature provides data for the coefficients of expansion; however the data given differ significantly from source to source. Thus, their utility as a basis for length compensation is limited, as becomes visible in the data for steel, for example. A temperature change of even a few degrees can result in deviations of several micrometers in compensation values calculated from an inaccurate coefficient of expansion.

The scanning heads for the LIDA 400 are a standard size, so they meet all requirements for reading the scales of glass and glass ceramic. Also, the identical cross section of the scales allows the graduation carriers to be exchanged.

POSSIBLE METHODS OF ASCERTAINING THE COEFFICIENT OF EXPANSION α
A coefficient of expansion can be measured exactly by a dilatometer, which is a device for measuring thermal expansion. With a well-designed dilatometer it is possible to attain exact data on a material’s coefficient of expansion by measuring a test object and use it to manufacture encoders.  An example is the “alpha measuring station” for measuring the thermal length expansion of bar-shaped bodies. Such a measuring station has been set up at the Physikalisch-Technische Bundesanstalt, Germany’s national metrological institute in Brunswick.

This exactly measured value can then be applied to calculate length compensation. In most cases, companies manage as best they can with data from the literature or the material manufacturer. This makes uncertainty in the result inevitable.

TEMPERATURE AND ACCURACY COMPENSATION
Special care must be taken in setting up a shop-floor measuring machine. Years of experience by the manufacturer result in high reliability and ensure high accuracy in spite of harsh environmental conditions. No compromises in accuracy are made compared with machines in measuring rooms.

Thermal effects must be dealt with through the appropriate know-how, the selection of suitable materials, and providing for thermal requirements. Because temperature increases expand materials to different degrees and these materials take on the surrounding temperature at different speeds, complex calculations are conducted to compensate the effects of temperature and accuracy. A known basis for mathematical compensation is very important—the linear encoder.

Thermally stable encoders are an indispensible prerequisite for basing calculations on accurate measurement data and thereby achieving accurate compensation. The selection of encoder material for shop floor measuring machine is therefore particularly important. While glass or steel scales permit only an approximate value for calculation, the expansion coefficient of 0+/- 0.1 x 10-6K-1 ZERODUR® for glass ceramic scales remains accurate over a large temperature range, and the scales have proven to be durable. The material is used the world over on telescopes, for example, because they place very high requirements on resistance to temperature changes and on distortion-free imaging.

THERMALLY STABLE ENCODERS
The right encoder enhances machine characteristics and contributes significantly to the reliability of the measuring machine. The area of production-integrated measurement is characterized by the following requirements and characteristics:

• Encoders with defined coefficients of expansion
• High accuracy for deviation between compensation points
• Minimal contamination for disturbance-free measurement
• High reliability over a long time period
• Cost-efficient encoders

One type of encoder that meets these requirements is the LIDA 400 exposed incremental encoder. Features include high accuracy and liberal mounting tolerances, high traversing speed, and the small height of the scanning head.

These attributes make it well suited for use on production equipment in automation engineering and the electronics industry as well as for applications on linear drives and in many areas of metrology.

The introduction of new graduation carriers of glass and glass ceramics, such as ZERODUR® and ROBAX®, have expanded the range of applications covered by encoders. They therefore suit applications in shop-floor measuring machines. They are easily installed by the PRECIMET® adhesive film on the back.

The scanning heads for the LIDA 400 are a standard size, so they meet all requirements for reading the scales of glass and glass ceramic (ZERODUR®, ROBAX®). No special scanning heads are needed. Also, the identical cross section of the scales allows the graduation carriers to be exchanged. From the logistical point of view this is a great advantage because the standard LIDA 48 (1 VPP) and LIDA 47 (TTL) scanning heads can be combined with glass ceramic and glass scales as well as with steel scale tapes. The identical carrier cross section of glass ceramic and glass scales make it possible to upgrade existing measuring machines. All designs have the same scanning surface of 14.5 mm², which ensures high tolerance to contamination and generates very clean scanning signals, which can be highly interpolated.

The encoders of the LIDA 400 series have a grating period of 20 µm. They are available in the widely used 1VPP and TTL interfaces and for measuring lengths of up to 30 m (steel) or 3 m (glass and glass ceramic). Traversing velocities up to 480 m/min are possible. The encoders are available with
reference marks as well as integrated magnetic limit switches.

Today’s changing requirements on machines such as measuring machines or production equipment in the electronics industry call for encoders that are also capable of meeting these demands. The problem of thermal expansion can be solved by the proper selection of different graduation carriers that are uniformly capable of using the same model of scanning head.  In conjunction with measuring standards of glass and glass ceramic, the new generation of LIDA 400 exposed linear encoders offer ideal properties for accurate measurement even on shop floor and in production-integrated machines.

HEIDENHAIN
www.heidenhain.com

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The METALLUR process

HEIDENHAIN has developed a process—known as the METALLUR process—for manufacturing graduations on glass, glass ceramic, or steel.  The quasi-planar graduation structure provides optimum protection against contamination and thereby greatly enhances encoder reliability. The manufacturing processes are environmentally friendly and do not use chemicals such as those generally needed for etching.

Mechatronics on the Trail of Global Warming

By Donna Sandfox

Omron Electronic Components, LLC

A new highly portable mechatronic system to measure harmful pollutant relies significantly on a MEMS flow sensor

Figure 1. Stationary Aethalometers are used throughout the world, but have been too heavy to be truly portable until now.

Carbon dioxide is well known as a major contributor to global warming, and there are many ways to detect and measure it. But it is not the only culprit. Scientist have found that the second most significant contributor is soot, or black carbon. Not only does black carbon contribute to environmental degradation, but these tiny particles also cut short the lives of seniors and sicken children. A recent economic impact study in California’s San Joaquin Valley (The Benefits of Meeting Federal Clean Air Standards in the South Coast and San Joaquin Valley Air Basins, November 2008) has identified the cost of air pollution and estimated it at more than $1,600 per person per year.

Black carbon doesn’t stay in the atmosphere as long as carbon dioxide, so controlling it has the potential to achieve major benefits in the short -term. Some of the major emitters of black carbon are diesel engines plus wood- and coal- burning fires. However, to analytically determine the source of black carbon and recommend effective changes to correct the problem, scientists require instruments capable of measuring black carbon in the field.

Manufactured by Magee Scientific of Berkeley, CA, the Aethalometer, is an instrument that uses optical analysis to determine the mass concentration of black- carbon particles collected from an air stream passing through a filter. However, until recently, these instruments were too large and bulky to be easily moved to a suspected point of origination for black carbon; the smallest device (the AE42) weighed approximately 25 lbs and measured 11 x 12 x 8 in. The instruments collect data from installations located around the world (Figure 1), but these only give scientists local samplings.

To get a complete picture of the black-carbon problem, scientists required a very small portable Aethalometer to easily determine black- carbon readings in almost any location. A reduction in size required some clever engineering and component sourcing.

Figure 2. The AE51 Aethalometer’s designers took advantage of the flow sensor’s port placement by designing the manifold to interface to them directly without tubing.

Aethalometer operation

Aethalometers function by measuring the amount of particulate deposited on a fiber filter by a specific amount of air passing through the filter for a predetermined amount of time. This mechatronic system needed to incorporate mechanics, electronics, and computing in one compact package. One of the major size reduction obstacles to overcome was finding a small, lightweight, highly accurate flow sensor with low power consumption. Having worked with Omron in the past, the engineers from Magee Scientific again called on Omron for a solution to their requirements, and the company recommended its D6F-P MEMS mass flow sensor for gathering the required air samples.

Figure 3. D6F-P flow sensors are individually calibrated before shipping to deliver excellent repeatability results.

Size and power constraints

The body of the D6F-P measures just 10 mm high by 23.3 mm wide by 27.2 mm deep, and with a weight of just 8.4 grams, it fell within the size and weight restraints set forth by Magee. Designed for easy installation, the D6F-P has both the input and output ports on the same side which facilitates the connection of tubing.

Magee engineers made clever use of this feature, designing their new AE51 Aethalometer so that the sensor ports would mate directly to their manifold, without the need for tubing (Figure 2). Since this miniature Aethalometer was to be battery powered, current consumption was a concern. The D6F-P proved to be very efficient, drawing a maximum of only 15 mA while operating on 5 Vdc.

Accuracy and repeatability

The AE51 relies on calculating the exact amount of air, driven by a blower incorporated in the device for a given time. Therefore the flow sensor would have to be very accurate. The D6F-P’s flow range/ pressure range of +1.0SLM (+0.84 in H2O) with an accuracy of ±5% F.S. maximum and ±2% F.S.

typical would deliver the precise flow readings Magee required to obtain reliable measurements.

Additionally, since the sensors are individually pre-calibrated at the factory for high repeatability, Magee Scientific’s finished device adjustment and test time was kept to a minimum (Figure.3). Durability was also a concern since the AE51 would have to take multiple readings, but the sensor’s MEMS technology has been proven to deliver a long life with excellent repeatability.

Figure 4. A patented dust segregation system with dual centrifugal separators ensures that the sensing chip remains clean.

In the real world

Since the AE51 is designed to measure black- carbon particulate in areas of known high concentration rates, the sensor had to be reliable in these dirty, real- world environments. Measurements would need to be taken at busy traffic intersections, bus stops, industrial sites, and coal-burning power plants.

The AE51 would also be used in remote areas of the world where use of wood fires to cook and heat is common. Although the filter used to measure the density of the black carbon is in front of the sensor’s inlet, if any particles that got past were to effect sensor operation, measurement accuracy would be compromised.

Figure 5. The reduced size of the hand-held AE51 is obvious when compared to the rack mount AE22 Aethalometer behind it.

To prevent that occurrence, the D6F-P design uses a patented dust segregation system (DSS). The DSS in the flow path incorporates dual centrifugal chambers, in which particulate matter follows in the outer path away from the MEMS sensor chip regardless of the flow direction. Thus there is practically no degradation in sensor performance over the lifetime of the system.

Keeping the MEMS sensor chip clean lets Magee guarantee a long life for their Aethalometer without worry about black-carbon build- up harming the device’s performance (Figure 4).

The A51 Aethalometer (Figure 5) is so small that it can be strapped to a user’s belt, enabling the user to become the instrument’s legs and freeing the user to do other work while the meter is gathering information. It can also be tethered to weather balloons for upper atmosphere readings. Another potential application would allow the device to be carried by those whose health might be affected most by inhaling large amounts of black carbon. The AE51 would alert them to areas that have high concentrations of this toxic material.

Omron Electronic Components, LLC

www.components.omron.com

Yokogawa’s DLM2000 Mixed Signal Oscilloscopes

Tokyo, Japan-Yokogawa Electric Corporation releases the new DLM2000 series of mid-range mixed signal oscilloscopes (MSOs).

DLM2000 series mid-range oscilloscopes are compact, lightweight, and inexpensive. As such they present a new direction for mixed signal oscilloscopes, meeting customer needs in the increasingly digitized mechatronics and electronics fields. In the 200 MHz to 500 MHz bandwidth range, this product series delivers the highest performance in its class. An industry first, these MSOs are ideal for personal use and are being presented to the market under our new concept of “One person, one MSO.” Yokogawa aims to develop this new personal MSO market and capture the top share.

Development Background
In recent years, electronic devices and embedded systems have been built into products as varied as information appliances, automobiles, and industrial machinery. To inspect such products and analyze their performance, there is a growing need for oscilloscopes that can simultaneously measure analog and digital signals. According to our survey, approximately 70 percent of oscilloscope customers need to measure digital signals, and half of these need an oscilloscope with 8 channels or less.

However, the mixed signal oscilloscopes currently on the market are either waveform observation models without search and other analysis functions needed for software debugging or are large, expensive, and difficult-to-use high-range models for measuring ultra-high-speed signals in electronic devices. Customers therefore have no choice but to use a high-range mixed signal oscilloscope even for measuring digital signals having 8 channels or less. Yokogawa’s DLM2000 series mixed signal oscilloscopes are optimized for exactly this group of customers.

Product Features
1. Compact, lightweight, and inexpensive MSO for personal use
These compact (293 mm height x 226 mm width x 193 mm depth), lightweight (4.5 kilograms), and inexpensive MSOs are made possible by the newly developed ScopeCORE LSI engine, on which key oscilloscope technologies have embedded with a high density. This MSO is perfect for personal use.
2. Flexible MSO input
The fourth channel of these MSOs is a flexible MSO input that can be switched between analog and digital. Up to either 4 analog channels or 3 analog channels plus 8 digital channels (8-bit logic) can be input.
3. High-speed sampling and largest memory in its class
The maximum sampling rate of 2.5 GS/s is six times faster than that of the previous product series, and the maximum memory size of 125 Mpts is four times larger.
4. Intuitive, easy operations
Various menu and panel features enhance the ease of operations. These include improved waveform display on a screen that is two times larger than the previous model, the dedicated knobs according to frequency of use, and the use of eight languages in menus and panels.

Major Target Markets
Mechatronics related manufacturers in industries such as automobiles and industrial machinery Manufacturers of information appliances, AV devices, communication devices, and office equipment

Applications
Design and evaluation of electronic and electric circuits Development and debugging of electronic devices, microcomputers, and firmware on embedded devices

www.yokogawa.com

Mechatronic Tidal Simulation Assists Scientists

Scientists from London’s Imperial College are using the new RT3 version of the Reliance Cool Muscle NEMA 23 integrated servo system to reproduce the sub-surface pressure changes created by lunar tides in laboratory research experiments directed at improving oil recovery.

The unique abilities of the RT3 version along with the support provided by Reliance allow the scientists to concentrate on the research without having to spend time controlling and verifying the test system. Read more

On-Wafer Evaluation of MEMS Devices

Testing at Earliest Stages in Development Can Help Lower Costs of Microelectromechnaical Systems.

By Mitsuhiro Nakamura
Agilent Technologies, Inc.

Recently, various devices using MEMS technology such as pressure sensors, accelerometers, and RF MEMS have been commercialized. Additionally, new devices such as silicon microphones, are rapidly evolving. The MEMS market started with the automotive industry and has been expanding to consumer products such as cellular phones.

This MEMS market expansion also applies pressure on manufacturers to lower their costs per device. However there are few opportunities for cost reduction. The limiting factors include:

• Low yields due to the precision process
• Slow throughput due to application of the physical stimulus.

A recent study (item 1 in the Appendix) estimates that 80% of the total production cost is attributed to the device packaging process and how defective chip inflow to the packaging process can contribute to cost increases. Therefore, we will discuss how to evaluate MEMS elements at the on-wafer stage in order to lower the total production cost.

Read more

Integrate Test with Design and Analysis

The common definition of mechatronics does not include testing. Perhaps it should.

By Sugato Deb, Ph.D., MBA & Director Emerging Markets / Partnerships
National Instruments

In the traditional design process of parts and assemblies, engineers produce models, analyze their behaviors under operating conditions, and pass physical prototypes “over the wall” for test engineers to evaluate in a pass-fail mode. Any problems that come to light are “thrown back” for design changes that, though necessary, come at the cost of additional prototypes and development time.

If that wall could be broken down, with analysis and testing working together in a closed-loop cycle, both groups would reap benefits from the use of test-based input values to drive analysis models, the use of analysis results to recommend sensor locations and test scenarios, and faster and better product development cycles. Read more