Test & measurement


Optical encoders selected for ‘unique’ linear motor


velocity. KOVERY has designed a series of advanced linear motors, with integrated Renishaw encoders, that solve this problem. Linear motors are widely used in major


C


industrial fields including flat panel display (FPD), semiconductors, automation, medical diagnostics, 3D printing and machine tools. A linear motor is equivalent to a rotary synchronous motor with a ‘rolled-out’ stator and rotor. Instead of producing a torque for rotation, it produces a thrust force along its length. KOVERY is an ultra-precision motor


manufacturer based in Gyeonggi-do, South Korea. Dedicated to continuous R&D, KOVERY is a leading supplier of advanced high-precision linear motor systems. KOVERY precision motors use patented


technology to eliminate or minimise cogging forces that cause velocity ripple and increased bearing wear due to attraction between the stator and the mover parts of the linear motor. Renishaw’s QUANTiC series of incremental


encoders are employed in KOVERY linear motors for commutation and position control. KOVERY also uses other Renishaw metrology products including the EVOLUTE absolute optical encoder and the XL-80 laser system for machine calibration. The encoders are critical components that give reliable position feedback in challenging environments.


The Challenge


Most linear motors are ‘flat linear motors’ that feature a permanent magnet track under a series of electromagnetic coils (forcer). Precise control of the forcer is required to enable demanding motion control applications in fields such as semiconductor and FPD manufacture. Constant velocity control is essential for


many advanced industrial processes, but traditional motor designs give rise to cogging forces which generate ripples in the motor velocity. One option for designers is to use a


54


onstant velocity control is essential for many advanced industrial processes, but traditional motor designs give rise to cogging forces which generate ripples in the motor


slotless (ironless) flat motor that provides excellent control at the expense of higher thrust outputs. KOVERY has developed a unique range of motors that minimise cogging forces without sacrificing thrust. KOVERY president, Kim Houng-joong,


introduces the company’s patented technology, stating, “The linear motors on the market come in various forms. Each design has its benefits but there are always trade-offs. The unique linear motors developed by our company are the first to arrange the permanent magnets in the vertical plane, so that they pass between the pole pieces of the forcer coils. “This ensures uniform magnetic flux and an


independent magnetic circuit for each magnet track. Our design allows the motor strength to be increased, simply by increasing the number of tracks. The design effectively reduces the normal attractive force between the slotted iron cores and the magnet tracks without sacrificing thrust. In other words, the overall thrust of the motor is increased, and the maximum is at least twice that of a conventional linear motor. Other advantages include reduced weight, increased design freedom, simple assembly and a low cost of ownership,” concludes Houng-joong. Position encoders enable commutation of


linear motors to provide smooth motion and position control. Encoders with lower jitter and interpolation error are preferred as they allow more accurate position control and lower velocity ripple. Encoders for linear motors need two critical design features to work well - a readhead (sensor) cable with a small minimum bend radius and long cable-life to allow for crimping, kinking, and bending on the machine cable track; and a high maximum operating temperature to withstand the expected heat outputs from the motor coils when power is applied. If the readhead is installed close to the magnetic coils, the encoder must also be able to withstand strong magnetic fields.


The SoluTion


KOVERY uses a range of Renishaw optical encoders for its linear motors, including the advanced QUANTiC optical encoder.


KOVERY president Kim Houng-joong In semiconductor and FPD process


equipment applications, KOVERY linear motors are equipped with QUANTiC series encoders featuring 0.2 µm resolution, RTLC40 incremental scale and analogue or digital signal output. Motors for other applications employ Renishaw's EVOLUTE absolute optical encoder with RTLA50-S linear scale. Houng-joong continues: “KOVERY's linear


motors offer a range of specifications, and there are more than a dozen different stroke lengths alone. Sometimes, it is necessary to provide customised products with strokes up to several metres. We also expect that market demand for longer-stroke linear motors will increase. The QUANTiC encoder's RTLC40 steel tape scale is supplied on a convenient reel, which allows us to cut the exact length required for each motor, improving our operation flexibility. In addition, the short delivery lead times and excellent cost performance are all factors. Renishaw's encoders have improved the competitiveness of our products.” Advantages of QUANTiC encoders include


compatibility with industry-standard digital or analogue outputs, wide installation and operating tolerances of ±0.3mm (rideheight) and ±0.9° (yaw), high operating speeds of up to 24 m/s, low Sub-Divisional Error (SDE) down to ±80nm, flexible single-shielded cables for EMI protection, and an integrated set-up LED to aid installation. Enhanced diagnostic data can be accessed via


the optional Advanced Diagnostic Tool ADTi- 100 and free ADT View software. The ADTi-100 is ideal for difficult installations, in- field diagnostics and fault finding.


March 2022 Instrumentation Monthly


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74