Since the beginning of the 21st century, there have been efforts to combat climate change with environmental measures. In that vein, the improvement of energy efficiency is in constant demand in the automobile industry as well as other industries. When it comes to manufacturing gears, in order to improve their performance, it is necessary to make those gears more accurate.
However, as the trend toward EV continues, there is a growing demand for high-speed and high-torque gears driven by motors instead of transmission gears. With the miniaturization of gears and modules, changes have occurred in the required evaluation criteria. Together, with the accuracy evaluation of the gear single body, a shift in the combination evaluation of the gear pair with the meshing partner and the evaluation in the entire gearbox is occurring. As a manufacturer specializing in fully automatic gear measuring machines, we have responded to demands while asking for gears. In this article, we will introduce some of the functions and application examples.
Full automatic gear measuring machines
Introduction of CLP Series
The CLP Series (Figure 1) is an automated gear-measuring machine that inspects automotive transmission gears, small gears, and other high-precision instruments. The CLP series is a standard product with more than 2,000 units produced. The CLP-35SF is capable of installing workpieces with an outer diameter of 350mm and is also capable of dealing with module 0.1～12mm, load bearing of 150 kilograms, and heavy workpieces. The measuring shaft length of 800mm and the long object can also be measured. In addition, a variety of lineups such as CLP-65SF, CLP-120 for large workpieces, and CLP-15SF specialized for small workpieces are also available to meet a wide range of gear requirements.
With these wide lineups, the CLP series contributes to higher precision and more efficient gear measuring. As defined by the JIS B 1702-1 standard, gear measurement is mainly conducted by inspecting the waviness of the tooth flank for the tooth profile and the tooth-helix measurement. As for the pitch measurement, by evaluating the tooth spacing, the tooth size and meshing are inspected, and rotational transmission efficiencies are evaluated. We have succeeded in measuring gears by traditional methods and have succeeded in high-precision and high-speed measurement by high-speed positioning with an originally developed high-precision single-axis detector and a special control device. In the measuring machine, the tooth profile is detected by tracing the stylus to the tooth flank by contact type, and the evaluation is carried out according to the standard. It enables high-resolution detection of 0.1µm; high-precision and high stability also are realized.
The CLP series specializes in high-speed measurement of rotating bodies, and it also supports the measurement of tools such as worm gears, hob cutters, and pinion cutters, together with the measurement of cylindrical gears. In the pitch measurement, measurement at 3 seconds/tooth is carried out as a high-speed pitch measurement by using a rotation mechanism and a high-precision detector. In addition, the addition of the measurement of moving and contact lines is also an option. The corresponding software is improved with tendency control by dog tooth, phase difference measurement, frequency analysis, and control chart, and customization can be done if requested.
Introduction of DDSF Series
For further high-speed measuring and high reliability of the CLP series, the DDSF series is prepared as an upper model. The DDSF series keeps the convenience of the CLP series, but the direct drive mechanism and the granite part of the main body enable high-precision positioning together with quietness, high-rigidity, and vibration reduction. The speed of the CLP series is higher than 20mm/second on each axis, while the DDSF series is 40mm/sec on the X, Y, and Z axes. The C-axis is 10rpm.
It is structured so it is not easily affected by changes in temperature. In addition to measuring with a conventional 1D probe, a 3D probe can be added to realize multi-functions. With a 3D probe, special gears such as bevel gears and hypoid gears can be measured because they can be detected in all directions. In addition, by making it possible to measure the tooth-tip part and tooth-root part — which have been difficult to measure until now — and further measuring the shape and accuracy of the shaft part as a geometric deviation measurement, the accuracy of the whole work can be measured continuously. When measuring complicated shapes such as tooth tip and tooth root, the measurement operation is carried out by defining the nominal shape. The measurement result detects the difference with the nominal data and evaluates it as a measurement deviation.
In the DDSF series, the nominal shape can be measured in all complicated shapes. In the CLP-85DDSF corresponding to the maximum heavy 500 kilograms, high accuracy is similarly ensured even in the maximum outer diameter of 850mm, and it corresponds to the large work. (See Figure 2)
Tooth profile, tooth helix, and pitch measurement
In the inspection of the machining accuracy of gears, accuracy confirmation by tooth profile, tooth helix, and pitch measurement are mainly carried out. In the tooth-profile and tooth-helix measurement, it is usually measured by four divisions in many cases.
The purpose of this method is to evenly measure the number of cutting edges of a hob cutter. However, it is often necessary to add conditions such as a modification to the tooth tip or tooth root according to the machining conditions or to provide crowning in the direction of the tooth helix. It is possible to measure each tooth with a subdivision measurement, 3D graphic display, and total tooth measurement, when it is desired to carry out the measurement in more detail according to various conditions. The measuring speed can acquire a maximum of 20mm/s and a maximum of 10,000 points for each. Although the measurement time depends on the tooth size and measurement conditions, it is possible to carry out the measurement in about five minutes if the work is with module 2.0.
The new probe DSA-60R2 is adapted to measure both tooth flanks simultaneously, and the measurement is carried out at 3 sec/tooth. Recently, there have been many reductions in the size of gears themselves, and measures for small modules are also being promoted. By attaching a special stylus to the detection part, it is also possible to cope with module 0.1. (See Figure 3)
Meshing path of contact and contact-line measurement
The meshing path of contact and the contact line are the moving line of the pressure point of the helical gear and also the contact line in contact at the same time. The path of contact also affects the transmission error, and the contact line affects the load distribution when meshing. Since both of them affect the improvement of the meshing ratio, they are measured when the contact point is controlled by providing crowning on the tooth flank. The meshing path of contact and contact-line measurement of the tooth flank are also possible by the optional function.
Other measurements
The geometric deviation measurement enables not only the measurement of the gear part but also the relative measurement of the shaft part and the outer frame part, which are integral to the work. By specifying the machining standard in the drawing, it is possible to measure the cylindricity, roundness, straightness and runout
of the bearing part, mounting error of the gear part, face runout, and straightness. And, by using a stylus changer and measuring while changing a holder and a stylus diameter, continuous measurement is possible for inner-diameter parts, inclination parts, etc. (See Figure 4)
Approach to closed-loop
The purpose of gear measurement is to confirm the quality of machined gears, but the original purpose is to improve the quality. The gear-measuring machine discussed also has a mechanism to feed back the measurement results to the machine, so it can perform processing with higher quality. We do not manufacture the processing machines, but we cooperate with the processing machine manufacturers of each company to make a network connection with the processing machines to achieve smooth feedback. Closed loops can be connected with many processing machines by conforming to GDE (gear data exchange format VDI/VDE 2610) formats. In addition, it is also correspondent to the original format with each manufacturer, and wide connectivity is realized.
Tooth flank roughness measurement
In the conventional gear-measuring machine, the measurement of the waviness shape has been the mainstream, but it often has been processed in more detail by the polishing process of the tooth flank. In order to respond to the request, it also corresponds to the tooth-flank roughness measurement. Until now, roughness components have been separately measured in machining sites for quietness inspection. For the measurement of roughness in conventional gears, the work of installing the measuring part of the gear horizontally with the ground using a tabletop measuring instrument or a special measuring instrument and striking of the stylus part was necessary.
Still, in the case of gears, it was difficult to align the horizontal part with the helical direction of the involute part and tooth helix, and it was decided to measure the line different from the direction to be machined. It was also a problem that the measuring position differed by the operator, and the dispersion of numerical value and shape became a problem. In the discussed gear-measuring machine, not only is the dispersion of the measuring position prevented, but, also, the measurement of the machining line became possible by applying the tooth profile and tooth-helix measurement, and with a strict measuring position. By doing this, it is possible to catch the measurement along the machining line in the tooth-trace direction and the ruggedness by grinding the stone grain and hobbing mark in the tooth-profile direction.
Although different from the evaluation of waviness curves, the roughness standards (JIS B0601:2013) also define the evaluation of the traveling direction. Therefore, the analysis of high-frequency components is required. A diamond stylus with a tip diameter of 2 µm was used and a skid was also used to prevent vibration and disturbances in the machine. This enables an evaluation of fine shapes. (See Figure 5)
Bevel gear and hypoid gear measurement
As a special gear measurement, the measurement of bevel gears and hypoid gears is also possible. The tooth-flank profile of the bevel gear and hypoid gear is measured by a sphere stylus and a 3D probe. The nominal data as a theoretical value is used as a measurement standard, while the tooth flank is followed. For straight bevel gear measurement, the spherical involute profile is the theoretical value.
In spiral bevel gears and hypoid gears, the ring-gear pinion target tooth flank and its conjugate flank are made to be theoretical values, and the tooth profile and tooth helix measurement line are measured by scanning, and — similar to the cylindrical gear — the subdivision measurement is also possible. By using the conjugate flank as a measurement standard, analysis such as tooth contact and transmission error simulation is possible from measurement data.
Conclusion
While the requirements for gears are diversified, we continue to pursue accuracy and speed. As the demand for energy efficiency increases, gear-measurement technology will be required to be advanced as the machining method of gears and the inspection standard also advance. We continue to work on the sophistication of gear-measuring machines, developing more multi-functionality, high precision, and automation, to meet increased demands.
