A schematic diagram of calibrating the ball screw with 4 trigger pulses per revolution <br> <br> experiment along with the high data rate interface, PCMCIA card, and an outer series of flip-flops Doppler laser calibration system, at 10,000 per second data rate synchronous acquisition data constantly. Solid State Fertilizer Spreader Solid State Fertilizer Spreader,Solid Fertilizer Spreader,Biosolids Spreader,Fertilizer Spreader Buggy Gongzhuling Huaxi Agricultural Machinery Manufacturing Co.LTD , https://www.hxzbjx.com
In addition, static positioning errors are often caused by geometry, rails, and structural rigidity. Dynamic positioning errors that are not normally measured are caused by servo parameters, resonance frequency, and acceleration or deceleration. In other words, because the machine stopped before acquiring data, servo or dynamic errors were missed. In theory, the trajectory accuracy should be improved with a dynamic displacement error table rather than a static displacement error table. This is particularly important for mold makers because it must be ensured that the mold cavity is exactly the same as the complex geometry of the various surfaces.
Displacement Measurement Means In 1881 Michelson invented the interferometer. He later won the Nobel Prize for physics in 1907. The Michelson interferometer uses white light as the light source and uses fixed and movable mirrors. The Michelson interferometer has been used to measure distances or compare distances by calculating interference fringes. With the invention of the laser, a single-frequency He-Ne laser replaced the white light as a light source, and replaced the plane mirror with two corner cubes.
The single-frequency holmium laser beam is split into two beams by a beam splitter, half of the beam passes through a movable cube corner prism, and the other half is reflected to a fixed cube corner prism. The two reflected beams meet at the beam splitter when they come back. After precisely aligning all optical paths, the two encountering beams interfere with each other and generate interference fringes. Count the stripe with a small area photodetector. The change in intensity per cycle represents the half wavelength of the travel of the corner cube prism. If the wavelength of the laser is known, the movable cube corner travel can also be accurately obtained. The problem with single-frequency interferometers is that they are too sensitive to noise. Therefore, it is impossible to distinguish between electrical noise and gain drift from the movement.
A dual-frequency interferometer uses a dual-frequency neodymium laser to mix two different frequency beams to produce a carrier frequency. Therefore, the distance information carried is in the form of AC waves instead of DC waves. The problem with dual-frequency interferometers is the need for bulky permanent magnets and precision optics to stabilize the laser frequency, maintain polarization, and minimize scattered light back into the laser cavity. Because the system is bulky and has a large number of optical components, most machine tools need to open the machine cover when measuring.
Laser Doppler Calibration System <br><br><br><br><br> Laser Doppler Calibration System Laser Doppler Calibration System uses a Laser Doppler Displacement Measurement (LDDM), which combines microwave radar technology, Doppler effect, and optical heterodyne technology. LDDM uses electro-optic, optical heterodyne and phase demodulators to obtain the position information of the moving pyramid.
LDDM uses a laser beam to illuminate a mirror to measure displacement. The reflected laser beam changes in frequency as the mirror moves. Since the phase of the reflected laser beam is proportional to the position of the mirror, the change in position can be measured.
Polarization and dispersion of light are not a problem for LDDM and do not require sophisticated optical systems. The mirror can be inserted into the optical path at will, and a simple mirror can be used to reflect the laser beam to any angle.
How to use the laser Doppler calibration system
To calibrate an ordinary or ball screw, place a blade on the shaft and the motor drives the screw to trigger the position sensor. For example, four position sensors can be used to collect four sets of data per revolution. The position sensor sends a TTL pulse to the PCMCIA card to trigger data acquisition. The key to continuous data acquisition is the synchronization of external triggers and data acquisition with TTL trigger pulses, which means that data is collected simultaneously. The pitch error of a typical ball screw measured with four position sensors is 0.2 inch per revolution. Therefore, 20 data can be measured per inch over a 20 inch screw. In this example, the thermal expansion error is much smaller than the pitch error.
To calibrate an axis of a CNC machine, place the laser head on the bed, and the mirror or target is placed on the spindle. The laser beam is adjusted to parallel and the main axis as with a conventional static laser calibration. But unlike the usual five-second stop for each step, which ends at the end, the spindle is now adjusted so that it can move continuously from start to finish without any stopping.
The position sensor can be placed on the ball screw or on the ball screw's runner. Non-contact triggers are attached to the magnetic base. The trigger blade is placed on the spindle of the screw. Each time the wheel rotates, the trigger signal is sent to the PCMCIA card to collect data. Some machine triggers are output from the machine's controller or encoder. 
Atmospheric pressure sensors, air temperature sensors, and material temperature sensors can automatically compensate for measurement errors caused by wavelength variations. The material's thermal expansion is within the laser system's standard. The laser head of the LDDM is placed on the work platform, and the mirror is placed on the spindle of the vertical machining center. A non-contact trigger is fixed to the pole of a magnetic seat, and a trigger blade is fixed to the wheel.
Use a laptop with a high-speed PCMCIA card to collect data. The output of the LDDM processor is connected to a PCMCIA card with a specially made cable, and the trigger signal is connected to the LDDM processor. In the main menu of the LDDM software, the 2-D time base button is used to set the data acquisition. Select data rate, interval, and external triggers. The maximum speed is 5 meters per second and the highest data rate is 10,000 data per second. The data lifetime between the trigger pulse and displacement readout is less than 100 nanoseconds.
In the experiment, two laser heads were placed 4.25 inches (10.8 cm) apart in the Y-axis direction. Displacement data was collected using a conventional static data acquisition method, stopped every 2 inches and the entire stroke was 18 inches. The maximum error is 0.02 inches and the backlash is 0.005 inches.
Then set the same, and use the non-stop synchronous external trigger to collect the displacement data. With a 0.2-inch gap, the entire trip was 19 inches and data was collected after walking at least 5 times.
Two sets of LDDM displacement data were collected synchronously without stopping. The angle error can be calculated by dividing the difference between the two displacement errors by the separation distance. The maximum angle error is 8.5 arc seconds. The maximum straight line reading error is 0.00012 inches.
Compared to statically collected data, the results of synchronously acquired data are similar but with more detailed information. Using this displacement data to compensate for the machine tool's error is better than that of the conventional static acquisition data. In addition, the use of synchronous data acquisition saves time, especially for measurements in small intervals or on large machine tools.
Measure method to save machine calibration time
The conventional method of measuring the displacement error of a CNC machine tool is static—the machine must be stationary for a few seconds at each measurement interval, and then the positioning data must be collected. For measurements on small pitch or long stroke machines, this means considerable downtime. The same measurement, using uninterrupted synchronous data acquisition, takes only a few minutes. In fact, continuous, synchronized data acquisition can also measure more points, provide more detail and save time. For example, if you want to stop for 5 seconds every 25 mm interval, the 1,250 mm shaft length and 5 round trips will take more than 50 minutes.