Large-scale mechanical equipment, such as turbines, steam turbines, large generator sets, large bearing rings, etc., often require high-precision measurement of its large diameter to meet the control of the diameter size in the machining process. Large-diameter measurement must solve a series of special problems such as small measurement and on-line measurement. At present, the following methods are used: 1 The measurement is performed with π rule. The method is simple, but the measurement error is large and the accuracy is difficult to improve. 2 If a large caliper is used for measurement, if the caliper increases with the increase of the measured diameter, there will be many insurmountable difficulties. 3 Although the electronic caliper measurement accuracy is high, the measurement range is still limited. The 4 scales are a more advanced measurement method, but large scales are very expensive and it is not easy to measure online. 5 Measure the circumference of the part under test with a roller, and then calculate its diameter. The advantage of this method is that the geometry of the workpiece to be tested is not limited, it can measure small and can be easily measured online, which is also decades, The reason why people have never been abandoned is always. Roller method is theoretically error-free, but because the technology is not perfect, if you do not solve the problem of slippage between the contact point of the roller and the measured workpiece, it will bring errors to the measurement and limit the improvement of its measurement accuracy. How to solve the slippage problem of the contact point between the roller and the measured workpiece is the key to perfect this technology.

1 Roller Measurement Principles and Measures to Improve Accuracy

The principle of measuring large diameter by the roller method is shown in Figure 1. It is the use of the roller to measure the circumference of the workpiece to be measured, the use of the circumferential length and diameter of the functional relationship, through the calculation to determine the diameter of the device is measured:

D=L/Ï€

Figure 1 Roller diameter measurement

Where L is the perimeter of the device under test, it can be seen that the accuracy of the diameter D of the device under test depends on the measurement of the perimeter of the device under test. Therefore, when measuring, the roller should be in contact with the device under test with certain pressure. The roller is used for the non-slip pure scrolling relative to the device under test. When the DUT rotates, the transmission relationship between it and the roller is:

n π d=N π D

D=(n/N) d (1)

In the formula: n is the number of revolutions of the roller; N is the number of revolutions of the part to be tested; d is the diameter of the roller; D is the diameter of the DUT to measure the diameter of the roller. This solves the problem of small measurement and facilitates on-line inspection. However, the precondition is that when the device under test (hereinafter referred to as workpiece) and the roller rotate, there should be pure sliding between them without sliding, that is, there is no slip phenomenon. However, the slippage phenomenon has always been a problem that is difficult to solve due to the large diameter of the roller method. For this reason, we have taken some measures in this measurement method to reduce the slippage.

1.1 Solve the problem that the axis of the DUT is not parallel to the roller shaft During the installation process, the axes of the tested workpiece and roller should be parallel to each other, as shown in Figure 2(a).

Figure 2 The effect of the non-parallel axis of the roller axis and the DUT axis on the measurement

Only in this way can they be guaranteed to rotate in the same plane in each radial section. If the pressure deformation between the two wheels is not taken into account, the contact between them is point contact, as in point A in Figure 1. Because it is a pair of rollers, they have the same linear speed of rotation and rotate in the same plane. Therefore, at point A, the relative speed of the roller and the workpiece is zero, and the arc lengths they turn are equal to each other, indicating that there is no slip phenomenon. The diameter of the workpiece can be accurately measured. However, when the workpiece and the roller are installed, the workpiece axis and the roller axis may not be strictly parallel, and the roller axis deviates from the workpiece axis by a certain angle θ, as shown in (b) and (c) of FIG. 2 . Because the rotation of the workpiece is provided by the drive device, and the rotation of the roller is dependent on the rotation of the workpiece. Because the two axes are not parallel, the workpiece and the roller do not rotate in the same plane when rotating, causing their rotation speeds to be different. From (b) and (c) of Figure 2, see:

v roll = v cos θ

The rotation speed of the roller will be less than the rotation speed of the workpiece, resulting in slippage. The arc they turn is no longer equal. The measured diameter will become smaller. If a fine adjustment mechanism is designed to allow the roller shaft to swing near the position parallel to the workpiece axis, the larger the angle θ between the roller axis and the workpiece axis, the smaller the measured workpiece diameter. Adjust the fine adjustment mechanism so that the angle θ gradually decreases, and the measured workpiece diameter gradually becomes larger. When θ = 0, the two axes are parallel, and the measured diameter is the largest. The fine adjustment mechanism continues to increase the angle θ in the opposite direction, and the measured diameter decreases, as shown in FIG. 3 . Only when the measured diameter is maximum, it indicates that the roller axis and the workpiece axis are parallel at this time, namely the maximum position in the figure. Mount the roller shaft in this position to avoid slippage.

Figure 3 Influence of the included angle θ between the roller axis and the workpiece axis on the measured diameter

1.2 Reduce the friction force of the roller shaft When the roller rotates, the roller shaft and the bearing must produce friction. This friction force directly affects the rotation of the roller. We hope that the friction force is as small as possible to reduce the slippage. . Therefore, it is ideal to use air bearings with very small friction, so we designed and conceived the top structure of air flotation, as shown in Figure 4. The top is made hollow and can be ventilated. The upper and lower ends are respectively filled with high-pressure gas. The hole throttling method is used in the figure. When compressed air passes through the center hole, it will overflow from the gap. There is a small section of the top seat and the top part that is ground. The two walls are closed under static conditions. When the gas passes in, the two top ends produce a slight separation due to the gas pressure, forming a taper gap, and the rest of the top seat and the top. There is a slight difference in angle, forming a wedge-shaped gap. The upper and lower tops are supplied with the same pressure, and the roller's own weight makes the air gap at the lower tip lower than the upper tip. Therefore, the flow rate of the gas overflowing from the lower tip is small, and the flow rate at the upper tip is large. On the other hand, the high-pressure gas enters the air chamber through the orifice type throttle, and the same structure of the throttle is used at the top and bottom, and the resistance to the flowing gas is the same. The pressure drop generated by the restrictor is proportional to the gas flow, so the pressure drop at the upper end of the restrictor is large and the pressure drop at the lower end is small, that is, the pressure in the upper end cavity is small, and the pressure in the lower end cavity is large. There is a pressure difference between the upper and lower air chambers. This pressure difference is related to the air supply pressure. When the air supply pressure reaches a certain value, the force acting on the top of the pressure difference is equal to the weight of the roller and the roller can be floated. Because of the existence of the air gap, the friction of the roller itself is extremely small, so it can be said that adopting the air floating tip structure is a further step in reducing slippage than the use of an ordinary bearing.

Figure 4 air cushion structure diagram

2 Data Acquisition

The data acquisition consists of two parts, measuring the number of revolutions of the part under test, N, and the number of revolutions of the wheel. First talk about how to get the number of revolutions N of the device under test.
A mark is made on the side of the device under test. When the mark passes through the photoelectric switch, the photoelectric switch will receive a light pulse. Every rotation of the workpiece, the photoelectric switch will receive a pulse signal. This signal is photoelectrically converted, the circuit is amplified, and the signal is shaped. After being sent to the computer for counting, the number of revolutions N of the workpiece is thus recorded.
From the formula (1), it can be seen that the number of turns n of the roller has a direct relationship with the diameter of the device under test. Therefore, the number of rotations of the roller n must be measured accurately. Therefore, Moire measurement technology is used. A circular grating is mounted on the roller shaft, the roller rotates one revolution, and the grating also rotates one revolution. A light bulb, a lens, and an indicator grating are mounted on the front of the circular grating, and a photoelectric receiving device is installed behind the circular grating so that a moving moiré is formed when the roller and the grating rotate. If the grating perimeter line is 10,800, the nature of the moiré fringe is known: there are 10,800 pulse outputs per rotation of the grating. When the computer receives the first pulse of the workpiece, it begins to count the moving moire fringe. When the tenth pulse of the workpiece arrives, it means that the workpiece has been transferred for 10 weeks (take 10 weeks to improve the measurement accuracy), The moiré count is stopped at this point. The number of movements of the counted moiré strips is taken out from the computer, divided by 10,800, which is the number n of turns of the scroll wheel. If the computer can accurately record the number of revolutions of the workpiece and the Moiré fringe signal generated by the grating, photoelectric conversion and circuit amplification are indispensable because the pulse signal received by the optoelectronic receiving device is weak and is an analog variation. And what the computer can accept is digital, so it is necessary to amplify the signal and convert the analog signal into a digital signal. Signal amplification We use a more commonly used inverting proportional amplifier circuit. This circuit has a simple structure. Due to the effect of negative voltage feedback, the input and output resistances are very small, so the ability to carry the load is strong. In addition, in order to get the digital quantity, a schmitt trigger is lapped with a 555 timing chip. The advantage of this circuit lies in: 1The input signal changes from the conversion level when the low level rises and the conversion level when the input signal falls from the high level, in order to improve the antijamming ability of the circuit. 2 When the circuit performs state transition, the edges of the output voltage waveform become steep through the positive feedback process inside the circuit. Using these two characteristics, not only can the edge change slow analog signal (sine signal) be shaped into a steep-edged rectangular wave, but also the high and low levels superimposed on the rectangular wave pulse signal can be effectively eliminated.
Counting with a microcontroller can make the circuit much easier, because the 8031 ​​microcontroller has two internal timer/counters, T0 and T1. Let T0 and T1 work in counting mode in software programming. T0 is used to record the number of revolutions of the workpiece. T1 records the number of moving moiré. When the number of pulses recorded on T0 is 10, the count of T1 is stopped immediately. Then the count of T1 is taken out, and the workpiece is calculated by formula (1). The diameter of D. In addition, the 8255 A is used as the parallel interface of the SCM to send the calculated diameter D to the LED for display. Among them, A and C ports of the 8255 A are used as output ports. The A port is used as the LED control and the C port is used as the position control.

3 Programming

With the above hardware, counting and calculation are completed until the diameter of the measured workpiece is displayed by the LED. The count is the number of revolutions of the workpiece being measured and the number of moire fringes generated by the raster. The diameter of the workpiece to be measured can be calculated from the number of moiré movements recorded. Figures 5 and 6 are the main program flowchart and the counting program flowchart, respectively.

Figure 5 main program flow chart

Figure 6 Flow chart of counting process

4 Conclusion

The conventional roller method measures large diameters on-line, and after taking effective measures to improve accuracy, the measurement accuracy and repeatability can be improved by an order of magnitude compared with not taking these measures. Therefore, using a roller method to measure large diameters online is still a convenient and effective method.

Connect cooling machine is combined with filtering into one. The function is to fast cooling the material by the circulating water inside. At the same time to filter the material.

The Main technical data:

Meal Cooling Machine

Meal Cooling Machine, Meal Cooler, Dead Animal Rendering Equipment, Animal Rendering Plant

Connect Group For Poultry Project , https://www.connectpoultry.com