With the popularization of CNC machine tools in the field of machine tool manufacturing, modern machine tools have also greatly improved in terms of processing speed, machining accuracy and reliability, which is largely suitable for grating measuring components for machine tools.
Single-field scanning technology and absolute measurement technology are the two most important directions in the development of current angle and length measurement technologies, and single-field scanning technology and absolute measurement technology can also be combined. At the same time, the single-field scanning absolute measuring equipment adopting these two technologies is far superior to the traditional measuring equipment in terms of signal quality, anti-polling ability, measuring speed and usability, and the rapid promotion of such products in the market is also This is confirmed.
Single field scanning technique
In the four-field imaging scanning method employed in conventional angle and length measuring devices, the grating scale is moved relative to a scanning mask having a similar or identical grating structure. The degree of light and darkness passing through the scale and the mask varies regularly according to the relative position of the scale and the mask: when the scale matches the gap of the mask, the light passes through; when the grid line coincides with the gap, there is no light. Pass through. The photosensitive element converts a change in light intensity into an electrical signal. There are four scanning areas on the scanning mask, and the scanning area gratings are shifted by 1/4 pitch from each Other, and the photosensitive elements corresponding to the four scanning areas generate four sinusoidal signals with a phase difference of 90°. These four scan signals do not use the neutral line as the neutral line, so the four signals need to be subtracted two to two to obtain two 90° phase differences, and the neutral line is the output signals l1 and l2 of the neutral line.
In the novel single-field scanning technique, the scanning mask has a large-sized grating whose pitch is slightly different from that of the grating scale, thereby causing an alternating light and dark phenomenon on the length of the scanning mask grating: some local grid lines Overlap with the gate line, the light can pass; in some places, the grid line overlaps with the gap, and the light cannot pass; between the two, the gap portion is blocked, which plays the role of optical filtering, resulting in a uniform high sinusoidal signal. become possible. A special grid-like photosensitive element replaces the independent photosensitive element to generate four scanning signals with a phase difference of 90°.
The single-field scanning optical scanning system plays a decisive role in improving the performance of the angle and length measuring equipment. Its large-area scanning area and special optical filtering produce a stable quality scan signal over the entire travel of the measuring device. This is a prerequisite for the following: small positional error during signal period; high raster running speed; direct drive When the quality is high.
This advantage of single-field scanning is clearly seen in the oscilloscope XY display mode: the output signal of a single-field scanning scale has better roundness and less signal noise, which means higher positioning accuracy and better Control quality. For linear motors, the speed control can be smoother with a single-field scanning scale.
A large-size scanning surface covering the full width of the grating scale and alternating strip-shaped scanning areas make the measuring device using the single-field scanning principle particularly insensitive to contamination interference, which can be confirmed by anti-pollution tests: even in large areas When the pollution is disturbed, the measuring device can still provide high-quality measurement signals, and the position error is far lower than the error value corresponding to the calibration accuracy level of the measuring device.
Compared with the four-field scanning, the single-field scanning can avoid the complete signal-free output of the device in some pollution interference situations.
Absolute measurement technique
The so-called "absolute measurement" is relative to incremental measurement. The incremental measuring device obtains the relative movement distance data by counting the raster lines scanned by the grating probe. In order to obtain the absolute position, the incremental measuring device must perform the reference point action after the power is turned on, and the absolute measuring device directly produces the absolute position data into the measuring device in the encoded form with the grid lines of different widths and different pitches, the measuring device Absolute position information can be provided after power on. In general, absolute measuring equipment is equipped with an incremental rail in addition to the absolute rail to further improve the accuracy and resolution of the measuring equipment.
In recent years, absolute gratings have been used more and more widely because of their irreplaceable advantages. These advantages are mainly reflected in the following aspects:
1. Reduce machine non-production time
During the use of the machine, it is often forced to shut down and restart due to malfunction or other reasons. For machines that are only equipped with incremental gratings, the reference point must be passed to each axis after power-on. The difference from the reference point after normal start-up is that the tool of the machine tool is usually still in the machining position, in direct contact with the workpiece, and sometimes even inside the workpiece (such as drilling, tapping, etc.), for safe operation. By reference point, the tool must first be manually moved out of the machining position. This is more difficult for multi-axis machines with tilting tools, which often takes a lot of time and labor, because when the tool is not parallel to the X, Y, and Z axes, it increases the difficulty of manually removing the tool after the fault.
For an automatic production line consisting of multiple processing equipment, when one of the equipment fails and needs to be restarted, it may be necessary to pass all the equipment in the production line through the reference point, and special processing is required for the workpiece that is not completely processed. The machine or production line equipped with an absolute grating regains the absolute position of each axis and the spatial orientation of the tool immediately after restarting, so that the original machining program can be continued from the interruption immediately, which greatly improves the effective machining time of the machine.
2. Improve machine toolability
The reliability of the machine directly determines the efficiency and economy of the part production. The machine's breakdown time per minute means an increase in cost for the user. Therefore, a trend in machine design is to monitor the status of important components in real time. HEIDENHAIN's absolute encoders support this type of real-time monitoring via its two-way communication EnDat data interface. In addition to the absolute position value, the EnDat data interface transmits the working condition of the grating to the numerical control system, such as whether the reading head light source adjustment margin is close to the limit, whether the maximum allowable moving speed of the reading head exceeds the standard, and whether the working temperature exceeds the allowable range. When the above situation occurs, EnDat can send an early warning signal to the CNC system. At this time, the grating can still work normally, but the user can take measures in advance according to the warning signal.
When a serious fault occurs in the grating, EnDat also sends an alarm signal to the CNC system. Based on this signal, the CNC system can decide whether to abort the machining to protect the machine and the workpiece. When troubleshooting, the maintenance personnel can find the root cause of the fault in the shortest time according to the information provided by EnDat, such as the grating power supply is too low, the read head is not working properly, and the output signal amplitude is too low.
By sending two levels of fault signals, such as warning and alarm, the absolute grating can greatly improve the efficiency of the user's maintenance work, reduce the probability of the shutdown caused by the grating failure, and the reliability of the machine tool is also improved.
3. Improve machine safety
In order to protect the mechanical movement of the machine, a travel switch can usually be used to ensure that the movement of the machine components does not exceed the permissible range. The travel switch has been in a harsh environment for a long time (coolant, metal scrap, etc.), which is extremely fragile, and the travel switch is rarely used when the machine is in normal operation, so it is impossible to determine whether its function is still normal at any time. In order to ensure work safety, the user has to check the status of the travel switch regularly. The machine with absolute grating can determine the position of the moving parts of the machine at any time. By setting the corresponding switch in the numerical control system, the travel switch can be omitted, which saves the maintenance time of the machine user and avoids the damage of the travel switch. Possible safety issues increase the safety of the machine when used.
Single-field scanning technology and absolute measurement technology are the two most important directions in the development of current angle and length measurement technologies, and single-field scanning technology and absolute measurement technology can also be combined. At the same time, the single-field scanning absolute measuring equipment adopting these two technologies is far superior to the traditional measuring equipment in terms of signal quality, anti-polling ability, measuring speed and usability, and the rapid promotion of such products in the market is also This is confirmed.
Single field scanning technique
In the four-field imaging scanning method employed in conventional angle and length measuring devices, the grating scale is moved relative to a scanning mask having a similar or identical grating structure. The degree of light and darkness passing through the scale and the mask varies regularly according to the relative position of the scale and the mask: when the scale matches the gap of the mask, the light passes through; when the grid line coincides with the gap, there is no light. Pass through. The photosensitive element converts a change in light intensity into an electrical signal. There are four scanning areas on the scanning mask, and the scanning area gratings are shifted by 1/4 pitch from each Other, and the photosensitive elements corresponding to the four scanning areas generate four sinusoidal signals with a phase difference of 90°. These four scan signals do not use the neutral line as the neutral line, so the four signals need to be subtracted two to two to obtain two 90° phase differences, and the neutral line is the output signals l1 and l2 of the neutral line.
In the novel single-field scanning technique, the scanning mask has a large-sized grating whose pitch is slightly different from that of the grating scale, thereby causing an alternating light and dark phenomenon on the length of the scanning mask grating: some local grid lines Overlap with the gate line, the light can pass; in some places, the grid line overlaps with the gap, and the light cannot pass; between the two, the gap portion is blocked, which plays the role of optical filtering, resulting in a uniform high sinusoidal signal. become possible. A special grid-like photosensitive element replaces the independent photosensitive element to generate four scanning signals with a phase difference of 90°.
The single-field scanning optical scanning system plays a decisive role in improving the performance of the angle and length measuring equipment. Its large-area scanning area and special optical filtering produce a stable quality scan signal over the entire travel of the measuring device. This is a prerequisite for the following: small positional error during signal period; high raster running speed; direct drive When the quality is high.
This advantage of single-field scanning is clearly seen in the oscilloscope XY display mode: the output signal of a single-field scanning scale has better roundness and less signal noise, which means higher positioning accuracy and better Control quality. For linear motors, the speed control can be smoother with a single-field scanning scale.
A large-size scanning surface covering the full width of the grating scale and alternating strip-shaped scanning areas make the measuring device using the single-field scanning principle particularly insensitive to contamination interference, which can be confirmed by anti-pollution tests: even in large areas When the pollution is disturbed, the measuring device can still provide high-quality measurement signals, and the position error is far lower than the error value corresponding to the calibration accuracy level of the measuring device.
Compared with the four-field scanning, the single-field scanning can avoid the complete signal-free output of the device in some pollution interference situations.
Absolute measurement technique
The so-called "absolute measurement" is relative to incremental measurement. The incremental measuring device obtains the relative movement distance data by counting the raster lines scanned by the grating probe. In order to obtain the absolute position, the incremental measuring device must perform the reference point action after the power is turned on, and the absolute measuring device directly produces the absolute position data into the measuring device in the encoded form with the grid lines of different widths and different pitches, the measuring device Absolute position information can be provided after power on. In general, absolute measuring equipment is equipped with an incremental rail in addition to the absolute rail to further improve the accuracy and resolution of the measuring equipment.
In recent years, absolute gratings have been used more and more widely because of their irreplaceable advantages. These advantages are mainly reflected in the following aspects:
1. Reduce machine non-production time
During the use of the machine, it is often forced to shut down and restart due to malfunction or other reasons. For machines that are only equipped with incremental gratings, the reference point must be passed to each axis after power-on. The difference from the reference point after normal start-up is that the tool of the machine tool is usually still in the machining position, in direct contact with the workpiece, and sometimes even inside the workpiece (such as drilling, tapping, etc.), for safe operation. By reference point, the tool must first be manually moved out of the machining position. This is more difficult for multi-axis machines with tilting tools, which often takes a lot of time and labor, because when the tool is not parallel to the X, Y, and Z axes, it increases the difficulty of manually removing the tool after the fault.
For an automatic production line consisting of multiple processing equipment, when one of the equipment fails and needs to be restarted, it may be necessary to pass all the equipment in the production line through the reference point, and special processing is required for the workpiece that is not completely processed. The machine or production line equipped with an absolute grating regains the absolute position of each axis and the spatial orientation of the tool immediately after restarting, so that the original machining program can be continued from the interruption immediately, which greatly improves the effective machining time of the machine.
2. Improve machine toolability
The reliability of the machine directly determines the efficiency and economy of the part production. The machine's breakdown time per minute means an increase in cost for the user. Therefore, a trend in machine design is to monitor the status of important components in real time. HEIDENHAIN's absolute encoders support this type of real-time monitoring via its two-way communication EnDat data interface. In addition to the absolute position value, the EnDat data interface transmits the working condition of the grating to the numerical control system, such as whether the reading head light source adjustment margin is close to the limit, whether the maximum allowable moving speed of the reading head exceeds the standard, and whether the working temperature exceeds the allowable range. When the above situation occurs, EnDat can send an early warning signal to the CNC system. At this time, the grating can still work normally, but the user can take measures in advance according to the warning signal.
When a serious fault occurs in the grating, EnDat also sends an alarm signal to the CNC system. Based on this signal, the CNC system can decide whether to abort the machining to protect the machine and the workpiece. When troubleshooting, the maintenance personnel can find the root cause of the fault in the shortest time according to the information provided by EnDat, such as the grating power supply is too low, the read head is not working properly, and the output signal amplitude is too low.
By sending two levels of fault signals, such as warning and alarm, the absolute grating can greatly improve the efficiency of the user's maintenance work, reduce the probability of the shutdown caused by the grating failure, and the reliability of the machine tool is also improved.
3. Improve machine safety
In order to protect the mechanical movement of the machine, a travel switch can usually be used to ensure that the movement of the machine components does not exceed the permissible range. The travel switch has been in a harsh environment for a long time (coolant, metal scrap, etc.), which is extremely fragile, and the travel switch is rarely used when the machine is in normal operation, so it is impossible to determine whether its function is still normal at any time. In order to ensure work safety, the user has to check the status of the travel switch regularly. The machine with absolute grating can determine the position of the moving parts of the machine at any time. By setting the corresponding switch in the numerical control system, the travel switch can be omitted, which saves the maintenance time of the machine user and avoids the damage of the travel switch. Possible safety issues increase the safety of the machine when used.
Baochuan Wire Mesh Products Co., Ltd. , http://www.anp-wiremesh.com