Photoelectric scanning of a Gray-code graduation according to the imaging scanning principle

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1 Electronics Volume Optimized Scanning in Absolute Rotary Encoders Did You Know... that a HEIDENHAIN ERA 4281C angle encoder and a LIP 581 linear encoder are vital components of the High Definition Airborne Gravity Gradiometer from GEDEX Inc. (Ontario, Canada), which, for the first time, can clearly see up to eight miles into the earth, identifying mineral (including diamonds) and oil and gas resources. This important gradiometer dramatically increases the certainty of discovery, lowers the cost of exploration and is fast, efficient and environmentally friendly. Called the GEDEX HD-AGG, it employs gravity to measure minute density variations to identify subsurface geological structures. This next-generation, highly sensitive, breakthrough technology is a quantum improvement over current methods. It is extremely sensitive and provides high definition images of valuable underground deposits that were previously invisible or overlooked. Contents Page 2 Page 6 Page 7 Page 8 Page 9 Cover story continued Meeting the Need for Miniaturization Interactive Semicon Booth HEIDENHAIN Opens New Building in Germany New Benefits with Redesigned Linear Encoder Program Visit HEIDENHAIN on the Road Dear Abbé: Accuracy of Feed Drives Photoelectric scanning of a Gray-code graduation according to the imaging scanning principle Rotary encoders for electrical drives are subject to high requirements: they are expected to function reliably and provide dependable measurement data in spite of their often harsh environments.the optimized scanning principle made possible by the serial-coded absolute track meets these requirements. Absolute rotary encoders with optimized scanning are distinguished by the high quality of their scanning signals and their significantly reduced sensitivity to contamination. An innovative scanning and evaluation unit permits both high interpolation and optimized control loop performance. Interpolation and position value generation within the rotary encoder permits reliable, purely digital data continued on next page The high resolution performance of both the linear and angular HEIDENHAIN encoders is key to the gradiometer motion isolation system, as it provides unparalleled accuracy in measuring the system kinematics as well as superior feedback measurements for motor commutation, said Eric Morrow, a GEDEX Controls System Specialist. GEDEX s ( resource discovery technology is mounted on a patented stability platform isolation system and allows the system to be flown even in moderately turbulent conditions. Kimberlite Diamond Field: Current Technology Fuzzy, confusing missed opportunity GEDEX HD-AGG Clear, unambiguous diamond discovery For more information, circle #1 on the reader service card.

2 Optimized Scanning continued from cover transmission and relieves the higher-level electronics. Also, because their safety-related functions comply with IEC , the rotary encoders now are ready for use in SIL-2 applications. These changes have no effect on the dimensions of the encoders; no mechanical changes of the motor dimensions are required. Controlled servo drives are used in many areas of automation technology, robotics and handling systems as well as in the drive technology of production machines and machine tools. The requirements regarding dynamics, speed stability and rigidity necessitate ever-increasing gain factors in the control loops. The position encoders used have a decisive influence on important motor properties, such as: Positioning accuracy Speed stability Bandwidth, which determines drive command-signal response and disturbance rejection capability Power loss Size The position resolution and the position error within one signal period are distinctly in the foreground. Decisive factors here are the scanning principle as well as the further processing of the scanning signals. Encoders from HEIDENHAIN generally operate according to the principle of photoelectrically scanning a regularly structured measuring standard. In the imaging scanning procedure, as it is used by absolute rotary encoders, for example, a structured graduated disk rotates relative to a scanning point. The incident light is converted into electrical signals by the photovoltaic cells. The absolute position information is determined from the graduation on the graduated disk. Scanning principle The scanning principle of rotary encoders with optimized scanning generates the absolute position value from just two graduation tracks: the absolute information is encoded in just one track on the newly developed graduated disk. The pattern of this serial code structure is unique over one revolution. The incremental track is located next to it. It is interpolated for the position value and at the same time is used to generate an optional incremental signal. The information in the two tracks is processed in the new, highly integrated electronics to form an absolute position value with high resolution (approx. 33 million measuring steps per revolution). An optical filter is used in the special scanning of the incremental track to produce very homogenous signals. Instead of the usual individual photovoltaic cells, one large-area, specially structured photosensor generates scanning signals with a good sinusoidal shape and high consistency, even at very different speeds, for each graduation track. Higher resolution better control The consistently good quality of the sinusoidal scanning signals resulting from the optimized scanning significantly reduces the position errors within one signal period. This is why reliable 14-bit interpolation is now possible in the rotary encoder. The high resolution achieved by this results in finer measuring steps, which in turn are definitive for the high control quality and the finely tuned velocity control. Conventional graduated disk with 13 Gray-code tracks Graduated disk with serial code track and incremental track Scanning signals shown as Lissajous figures Consistently accurate The serial code structure, located in just one track, combined with the optimized scanning principle, permits a high accuracy of the encoder, independent of the speed. This means that regardless of whether you are operating at the maximum speed or nearly at a standstill, the positioning accuracy is always consistently high. 2

3 Tolerance to contamination Theoretically, contamination is not an issue with sealed rotary encoders that are integrated in electrical motors. In practice, however, traces of oil from bearings, dust from the brakes and out-gassing from the motor coil can intrude into the rotary encoder. Due to the large scanning area over the entire width of the scale grating and the special arrangement of several scanning fields, encoders with optimized scanning are extremely insensitive to contamination. Newly developed scanning and evaluation electronics The significant reduction of individual components results in a decided improvement in reliability during manufacture and when in use. The most important factor here is the reduction of the scanning from 13 tracks to just two tracks, as well as the high degree of interpolation of the newly developed scanning and evaluation electronics. Position error within one signal period, shown over one revolution These electronics also make it possible to increase the range for the power supply voltage, so that it is now from 3.6 V to 14 V. This means that monitoring of the supply voltage in the encoder can be omitted, and so sensor lines and a controllable power supply in the subsequent electronics are no longer necessary. The combination of the new scanning and evaluation electronics with the EnDat interface offers important advantages. Since interpolation takes place within the rotary encoder, purely digital data transmission, which is less sensitive to noise, is possible. Since lines for the analog signals are no longer needed, the connection cables are less complex, meaning that simpler and thinner cables are possible, as well as smaller connecting elements. Since the entire position value is already available to the subsequent electronics, time-critical interrogations and calculation operations are avoided. The EnDat interface makes extensive monitoring and diagnosis of an encoder possible without an additional line. The Accuracy relative to shaft speed Influence of contamination on positioning accuracy (typical measured values) continued on next page 3

4 Optimized Scanning continued from page 3 PCB for absolute rotary encoders with optimized scanning (via opto-asic), and PCB with scanning via four photovoltaic cells diagnostic system generates error messages and warnings, and is a significant prerequisite for the high level of availability of the complete system. For encoders with purely serial interfaces, the valuation numbers provide the current state of the encoder and ascertain the encoder s functional reserves. The valuation numbers can be read from the encoder cyclically via the EnDat 22 interface without influencing the quality of the axis control. Rotary encoders for safety-oriented applications For future-oriented applications, the question of safety standards is becoming increasingly important. That is why the functional safety as per IEC was already taken into account when designing the new scanning and evaluation electronics. Scanning in the encoder simultaneously produces two independent position values that are transmitted using the EnDat 2.2 protocol to the EnDat master in the subsequent electronics. The EnDat master assumes various monitoring tasks, and provides both position values via two independent processor interfaces to the safe control. Safety-related position measuring systems from HEIDENHAIN are permitted as single-encoder systems in applications with control category SIL-2 (in accordance with IEC ) or performance level d (ISO 13849). Screen showing the valuation numbers as functional reserves (e.g., with IK 215) 4

5 Available rotary encoders with optimized scanning HEIDENHAIN is gradually converting its absolute rotary encoders to optimized scanning. The following variants are available: ECN 1325/EQN 1337 ECN 425/EQN 437 ROC 425/ROQ 437 Two rotary encoder models are already available for safetyrelated applications: ECN 1325 singleturn version ECN 1337 multiturn version More absolute rotary, angular and linear encoders will follow. Safety-related position measuring system, consisting of an encoder, the data transmission line and the EnDat master For more information, circle #2 on the reader service card. 5

6 Meeting the Need for Miniaturization with a New High Accuracy Linear Scale An increasing number of applications require ever-smaller components, especially in the semiconductor and electronics industries. HEIDENHAIN Corporation, long setting the standards for accuracy and reliability in measurement components (especially evident in the LIDA 400 exposed linear scale), is now offering even smaller linear scales with the LIDA 500 series in order to meet this need for constant miniaturization and reduction of mass. These new 20 µm incremental linear scales are useful where installation space is limited, and offer measuring steps of 1 µm to 0.1 µm. Their reduced mass gives them higher dynamic capability. The LIDA 500 scale series - LIDA 583 and LIDA each have two smaller scanning fields with double-field scanning. In order to compensate for the known disadvantages of small scanning fields, the signal is corrected online electronically, thus producing better signals. The LIDA 500 series features glass scales as the measuring standard, and each encoder has a reference mark at the midpoint. They feature a ± 5 µm accuracy grade and a high degree of immunity to contamination. Easy mounting is characteristic of HEIDENHAIN s LIDA encoders, and this is no exception. The series offers 1 Vpp or TTL interfaces. For more information, circle #3 on the reader service card. News: An Interactive HEIDENHAIN Booth at SEMICON With demonstrations and opportunities to manipulate product, HEIDENHAIN will showcase its wares at the annual SEMICON West 2007 Show in San Francisco, California (July 17-19). SEMICON is a leading trade show for those interested in semiconductor design and manufacturing. Multiple opportunities for product interaction will be available at the booth, including giving visitors the opportunity to mount an encoder (ERA 4000) by themselves, quickly and efficiently. Other opportunities include manipulating a working high accuracy exposed linear scale (LIP 200) which is an enabling technology encoder with specifications not seen before by the motion industry. Visitors will certainly have some first-time opportunities at the HEIDENHAIN booth this year, said Kevin Kaufenberg, HEIDENHAIN s National Sales and Product Manager, Electronics. In general, HEIDENHAIN s 50 x 30 booth will host a variety of available products, from exposed linear scales to a variety of other types of encoders. Technical staff will be on hand to answer questions and discuss trends and thoughts for the future. Private showings in a separate meeting room of some new high-end products will be available by appointment only. For more information, contact kkaufenberg@heidenhain.com. Stop by HEIDENHAIN booth #6170 to learn about the latest! 6

7 IS INTERESTED IN YOUR FEEDBACK Your comments about topics addressed in this issue and topics you d like to see in future issues: Name Company Title Address City State Zip Phone ( ) FAX ( ) Please add me to your mailing list. (Provide address above.) Please send me HEIDENHAIN s most current catalog: General NC Linear Digital Readout METRO/CERTO Gauges Measurement Inspection Angular Rotary Incremental Rotary Absolute Rotary Contouring Controls Point-to-Point Controls Servo Drive For further information, circle the appropriate number: Article #1 #2 #3 #4 #5 #6 333 E. State Parkway, Schaumburg, IL Phone: FAX: ELECTRONICS VOLUME HEIDENHAIN CORPORATION IS INTERESTED IN YOUR FEEDBACK Your comments about topics addressed in this issue and topics you d like to see in future issues: Name Company Title Address City State Zip Phone ( ) FAX ( ) Please add me to your mailing list. (Provide address above.) Please send me HEIDENHAIN s most current catalog: General NC Linear Digital Readout METRO/CERTO Gauges Measurement Inspection Angular Rotary Incremental Rotary Absolute Rotary Contouring Controls Point-to-Point Controls Servo Drive For further information, circle the appropriate number: Article #1 #2 #3 #4 #5 #6 333 E. State Parkway, Schaumburg, IL Phone: FAX: ELECTRONICS VOLUME HEIDENHAIN CORPORATION

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9 HEIDENHAIN Opens New Building in Germany to Accommodate Growth As 2006 closed as a record-breaking year for unit sales of HEIDENHAIN encoders, the company began the new year supported by the opening of a recently completed building at its world headquarters in Traunreut, Germany. This new, approximately 135,000 square foot facility is now in use for the purpose of encoder assembly and R&D, and is the largest single investment in the history of DR. JOHANNES HEIDENHAIN GmbH. The construction of HEIDENHAIN s new building began in July Prior to that, many of the encoder assembly operations in Traunreut had reached the limits of their capacity. The production volumes of several product groups had doubled in the years prior, and some had even tripled. The automatic assembly systems for rotary encoders were running in three shifts, often in six-day weeks. The new building, designated A30, has five floors, each with approximately 27,000 square feet and currently holds about 600 employees. The basement is divided into three approximately equal areas: the assembly area for high-accuracy encoders, primarily for OEMs in the electronics industry; the long-term testing for product qualification during the development process; and the technical facilities. The ground floor and 2nd floor (see figure) house the assembly area for linear encoders, rotary encoders and angle encoders. Large parts of the 1st floor are used for air recirculation of the production level below it; the remaining spaces provide break rooms for the production employees and offices for production planning and production engineering. The 3rd and 4th floors of the new building offer space for the offices and labs of the R&D for encoder mechanics, R&D for encoder electronics, and encoder quality assurance. The complete process of encoder assembly and packing takes place on the same floor. This makes it possible to improve both productivity and logistics and eliminates unproductive transports and storage that require additional accounting work. In several areas, the door-to-door times can be reduced. A larger column interval and large ceiling height enhance the existing areas for more flexible use, enabling engineers to react more quickly to changes in the product program and more easily adapt their manufacturing processes. It becomes much simpler to plan, set up and operate assembly systems. The controlled room climate improves process stability and quality, particularly in adhesive and joining processes. For more information, circle #4 on the reader service card. 7

10 New Benefits with Redesigned Linear Encoder Program LC Linear Encoder HEIDENHAIN Corporation announces updates and enhancements to its well-known, high-quality linear encoder program. The mechanics and electronics of HEIDENHAIN s LC Series absolute linear encoders have been fundamentally redesigned from the ground up to better meet today s measurement requirements, and now include three interfaces -- HEIDENHAIN s EnDat 2.2, FANUC 02 and Mitsubishi. Specifically, HEIDENHAIN s new encoder models are the LC 183 M and 483 M series with EnDat, FANUC or Mitsubishi. These encoders offer more electrical advantages than ever before, including making purely serial axis-control possible. The resolution of the absolute position value is 5 nm for encoders with an accuracy grade of ±3 µm and 10 nm for encoders with an accuracy grade ±5 µm with the EnDat versions. Also, regardless of the measuring length, the data word length is 32 bits and with a clock frequency of 8 MHz, the formation of the position value and transfer takes approximately 20 µs. Both output formats also incorporate the single-field scanning technique ensuring optimum signal quality, high traversing speed and contamination resistance. Maximum cable runs also have increased with the new interfaces. The lower-cost EnDat connection technology and common cable assemblies (LC 1XX / 4XX) further reduce costs and decrease inventory requirements. Encoder diagnostics take place via additional information in the serial protocol. Along with the new interfaces, changes to mounting methods have been made with these HEIDENHAIN absolute linear encoders in order to simplify their installation in a wide variety of applications. Encoders of the 400 series can now utilize a universal mounting spar when required, which allows for a cable outlet to the left or right. Available accessories also include clamps as an alternative that are mounted at fixed intervals along the measuring length to provide additional support. Encoders of the 100 series have a left and right cable outlet directly on the scanning unit. The unused socket connector is protected by a cap. For more information, circle #5 on the reader service card. Technical Tidbit: What Is an IP Rating? An IP rating number is often used when specifying the environmental protection afforded by enclosures around electronic equipment. The first number in this rating refers to the protection against solid objects and the second number against liquids. So, what does a BOX with an IP65 rating mean? It means this BOX provides a level of protection that has total protection against dust (no ingress) and it can be immersed in water (to a depth of 15cm 1m at this rating). Note: All HEIDENHAIN product catalogs specify the IP rating for any given product. 8

11 Dear Abbé This column promises to answer questions related to accuracy issues in measurement. HEIDENHAIN welcomes your questions. Dear Abbé, I read your technical paper, Accuracy of Feed Drives which discusses linear vs. rotary scales during machining, thermal issues and position errors. How do I check the accuracy of my machine? Sincerely, Diligent HEIDENHAIN s Accuracy of Feed Drives white paper is available at: heidenhain.us/accuracy Dear Diligent, HEIDENHAIN offers a number of devices specifically designed to check various aspects of your machine s accuracy and geometry. An important one is HEIDENHAIN s VM 182 comparator system, which incorporates a steel scale with a graduation of very high accuracy and a scanning head that moves over the graduation without mechanical contact. This device provides a comparative measurement versus the motor encoder/ballscrew at accuracy of ± 1 µm. In addition to determining the position error, the VM 182 also measures guideway error orthogonal to the traverse direction of the machine axis. The resulting error values can then be used for acceptance testing and will also provide clear benefits of linear encoders for machine tool positioning. The VM 182 achieves this by its design. During mounting, the scanning head is connected to the scale by an auxiliary carriage. The scale is clamped paraxially onto the machine table, and the scanning head is connected to the machine quill with a coupling magnet. The relatively large tolerances of the VM 182 facilitate mounting and adjustment. After mounting is completed, the auxiliary carriage is removed from the scanning head. Other HEIDENHAIN tools for machine tool inspection and acceptance testing include the KGM Grid Encoders and Double Ball Bar. Visit HEIDENHAIN on the Road HEIDENHAIN will exhibit at these remaining 2007 trade shows. Please stop by! SEMICON July Moscone Center North San Francisco, California The VM 182 comparator system on the table of a milling machine Motion error trace from a comparative measurement with the VM182 for determining static positioning accuracy and guideway error (ISO 230-2) National Manufacturing Week September Donald E. Stephens Convention Center Rosemont, Illinois Quality Expo September Donald E. Stephens Convention Center Rosemont, Illinois For more information, circle #6 on the reader service card. 9

12 By Kevin Kaufenberg National Sales and Product Manager, Electronics LIDA Encoding Technology Not Just Another Line Item You may have noticed HEIDENHAIN s most recent addition to the LIDA family of encoders with the LIDA 500 system. Unfortunately, most people see encoding technology as just another line item to order for the machine they are building. They don t realize its complexities until they get to this line item. With our breadth of line of encoder technologies, we would like to help the users of encoding technology understand the LIDA family and what it has to offer. First, the LIDA series of encoders consists of high quality exposed scales using the imaging principle. This means that an image of a series of lines is generated by an LED and a reticle inside the scanning unit, projected onto the scale graduation, then reflected back into the scanning unit for conversion to Sine and Cosine electrical outputs. This imaging principle works like a Vernier caliper and uses a large image window to average over many lines, so that the principle is highly resistant to contaminations on the scale. The scales themselves are now offered in different materials to consider thermal growth aspects of the machine. The main versions are usually steel tape with the graduation exposed onto the tape substrate. These steel tapes are usually then placed into an aluminum extrusion, so that if the tape is damaged in some way, the tape is easily removed and replaced in the same exact position. The extrusions also help to bridge gaps that the machine may have, where these gaps would give grief to the stick on scales. Other substrates available for the LIDA series are normal glass, Zerodur ceramic and Robax glass. These substrates improve accuracy and help define the thermal characteristics of the machine. With gratings that span from 20 µm to 200 µm, a full range of applications are met. From advanced semiconductor machinery to high-speed medical equipment to quick-and-dirty mounting on less precise axes, the LIDA 100, 200, 400, and 500 systems cover the bulk of midrange to less accurate applications. With various scanning unit sizes, three different ways to mount the stainless steel tape graduation, integrated limit switches, bi-directional reference marks at the same resolution as the incremental track, multitudes of resolutions from 200 µm down to 50 nanometers, and short wave accuracies to 200 nanometers, you ll be sure to find the right LIDA encoder for your application. And HEIDENHAIN is not yet done with the development side of this line. With more flexibility of cable routing, scanning heads able to read different graduations and improved scratch-resistant graduations, there is much more to come with this series! Stay tuned. HEIDENHAIN CORPORATION 333 E. State Parkway, Schaumburg, IL