Measures to improve the accuracy of the frame structure of printing equipment
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The overall structure of the printing press is based on two wall panels as supporting base parts. A large number of rollers, shafts, rollers and other parts are installed between the two wallboards, so that the continuously traveling substrates are arranged from the aligned shafts, rollers and rollers. And other functional mechanisms pass through. In the progress of the substrate, such as tension control, paper feeding, deviation adjustment, water supply, ink supply, printing (overprinting), cutting, paper feeding, paper delivery, numbering, drying, cooling, glazing and various guarantees The mechanism that automates the printing process. Among them, the outer side of a wall panel is equipped with various transmission parts to drive the rotation, axial or intermittent movement of the roller, the shaft and the roller inside the wall panel, thereby achieving various printing functions. On the outside of the other wall panel, various operating mechanisms are installed to control the quality of the printing and ensure the smooth printing. Therefore, under the premise of ensuring the processing quality, the quality of the assembly quality of the wallboard will directly affect the quality and accuracy of the whole machine. As the main basic component of the printing press, it also affects the quality and life of various functional parts throughout the printing process. Paying attention to the research of basic components is an important means to improve the internal quality of printing presses. This paper prepares from the existing assembly positioning process method, analyzes the cause of the positioning error of the main basic parts through the calculation of the positioning error, and proposes several alternative new assembly positioning methods to improve the assembly positioning accuracy and further improve the printing. the quality of. At the same time, it is also the assembly method and means provided by the printing enterprise for the large and medium-sized printing presses.
First, the traditional process method produces the calculation of the coaxiality error
The traditional positioning method of the coaxiality accuracy of the basic parts mostly adopts the mandrel positioning mode. In theory, this method can achieve the three-way design basis, assembly benchmark, and positioning benchmark. The coincidence of the benchmark can improve the assembly accuracy. However, due to the shape, position error and dimensional error of the wall positioning hole, the positioning part of the mandrel is also given a tolerance value. Therefore, when the two wall plates are positioned by the mandrel, the existence of the gap will be flexible even if the mandrel is rotated. Coaxiality error is generated. Obviously, as the distance between the two wall panels is increased, the coaxiality error value is proportional to the wallboard spacing and proportional to the gap size. Due to the existence of gaps in large-span printing press wall panels, the resulting coaxiality error cannot be ignored. Although the relative position between the roller, the shaft and the roller can be determined from the common axis after the assembly of the roller, the shaft and the roller, it seems that the influence is not large, but the numerous transmission, steering and automatic control parts are in poor working conditions. More importantly, the accuracy retention is poor.
In order to establish the relationship between the gap, the wallboard spacing and the coaxiality error, the following constraints are first proposed:
1. The lower plane of the wallboard is the supporting reference and the guiding reference during processing. Therefore, it can be considered that all the co-located holes on the two wallboards are consistent with the supporting reference height dimension. When assembling, the horizontal position of the two wallboards is determined by the positioning core. Axis positioning determination;
2. It can be imagined from an intuitive point of view that the position at which the maximum concentricity error is generated is that the two ends of one hole are positioned diagonally with the positioning mandrel, and the other end of the hole is positioned to contact the mandrel. In theory, this When turning the mandrel, it should also be flexible; or the vertical processing can be combined on the workbench (it can also be divided and processed), so it is considered that the axes of the two wall plates are in the same direction, but the angle of the large plane of the wall plate is different, which reflects Consistent accuracy of the pull-shaft (tension beam) parts;
4. Generally speaking, the two wall panels have the same aperture. In order to make the derived relationship have universal significance, the two corresponding holes are unequal diameter holes.
Second, the coaxiality error analysis
The coaxiality error generated by the positioning and assembly of the three basic parts of the printing machine according to the current assembly process can be calculated by using the three relations previously derived. (1) is a general calculation formula for the coaxiality error, but does not include the error caused by the consistency of the pull shaft and the pull beam. Equation (4) is a simplified calculation of the concentricity error, that is, the variables in the equation are in line with the reality of the printing press. (6) The formula is a comprehensive calculation formula of the coaxiality error, that is, the calculation formula of the two factors of the gap, the pull shaft and the pull beam consistency error.
The same kind of situation can be applied to the coaxiality error analysis:
1. Only consider the concentricity error caused by the influence of the gap and the positioning mandrel;
2. Comprehensive consideration of the coaxiality error caused by gap and consistency;
3. Use the maximum value method to find the maximum coaxiality error;
4. According to the method of total quality management, consider the normal distribution of errors caused by machining and assembly, and obtain reasonable coaxiality error.
When the wall plate is positioned by the positioning mandrel, the operator has to rotate the mandrel to make it flexible. When the two wall plates are machined to prevent measurement errors, the operator also controls the aperture to the lower limit, and the diameter of the positioning mandrel is controlled at the upper limit. Thus, the actual resulting coaxiality error is smaller than the above calculation. According to the principle of total quality management, the maximum concentricity error calculated as above is only 3 parts per million (the standard deviation is controlled within 6σ). The process capability index of this positioning method is relatively high because there are fewer factors affecting the positioning accuracy. If the process capability index cp=1.33, the first two calculation results can be calculated by the following formula to calculate the accuracy of the coaxiality actually achieved.
Due to the existence of the gap between the wall plate hole and the positioning mandrel, the dimensional error of the pull shaft and the pull beam exists. This assembly positioning method produces a large coaxiality error. From the calculation results and the relationship derivation process, the following conclusions can be drawn.
1. The main cause of the coaxiality error is the gap between the wall plate hole and the positioning mandrel. As the positioning mandrel wears, the coaxiality error will continue to expand.
2. The consistency accuracy of the pull shaft and the pull beam also affects the accuracy of the coaxiality, but a secondary factor. In the actual processing, the measurement method of controlling the consistency accuracy by the card gauge is not acceptable. Experiments show that the measurement accuracy of the tube deflection is only about 0.4 mm, so the influence on the coaxiality is increased. If double-sided milling is used for each piece, the accuracy is increased by 60%, and the consistency accuracy can be controlled within 0.04mm. At this time, the card only plays a role in controlling the size of each batch of parts. Therefore, this paper no longer studies the issue of further improving the consistency accuracy.
3. It can be seen from the relationship that the coaxiality error is directly related to the wallboard spacing l and the wall thickness b. When the wallboard spacing is small or the thickness of the wallboard is large, the calculation of the front formula can ensure the accuracy of the coaxiality or the current mandrel positioning method can be used. The wall panel made of steel plate material has a large coaxiality error because of the small thickness.
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Third, measures to improve assembly quality
1. Improvement of traditional positioning methods
It is convenient to use the positioning mandrel assembly, and it has been used for many years of use, and the improvement of the positioning method can also achieve better coaxiality precision.
One method is to rotate the mandrel to measure the perpendicularity to the large face of the wall panel based on the flexible rotation of the mandrel. Another method is to move the two walls in the parallel direction in the parallel direction to the farthest distance of the flexible rotation of the mandrel, and then take the middle method. The specific practices are as follows:
(1) The first wall panel is fastened with a plug;
(2) installing a second wall panel and pulling the shaft and pulling the beam, and loading the positioning mandrel;
(3) Fix a dial indicator at one end of the wallboard and press the meter;
(4) Move the wall panel in a direction parallel to the wall panel, find the farthest point where the positioning mandrel is flexible, and read on the dial gauge;
(5) Move the wall panel in the opposite direction to find the other farthest point where the positioning mandrel is flexible and read on the dial gauge;
(6) Calculate the midpoint reading value (refer to the dial gauge reading) by the reading interval of the two farth points;
(7) Move the wall panel to the midpoint reading position.
By adopting this method, the coaxiality error caused by the gap between the positioning mandrel and the wall plate hole can be eliminated, and the midpoint reading position should be the center line position of the first wall plate hole, and the accuracy can reach a very high level. . Since the magnitude of the rotational moment is not specified when the mandrel is rotated, there may be an error in the farthest point obtained. In addition, when calculating the far-point reading, the smaller the step size per moving wall panel, the more accurate the farthest point is, which also affects the accuracy of the farthest point. In order to improve the assembly accuracy, the smaller the moving step is, the better the wall panel moves closer to the farthest point. If the 0.05mm moving wall panel is used to test the positioning mandrel rotation flexibility, the reading at the farthest point will have a reading error of 0.05mm. The center reading error is 0.025mm and the coaxiality error is 0.05mm. If the step size of the wallboard is reduced near the farthest point, the accuracy of the farthest point measurement can be improved, and the coaxiality accuracy can be improved.
The method of moving the wallboard can be tapped, but it is better to make a tool that pushes the wallboard by the force of the screw and can receive better results.
2. Measures to ensure coaxiality by pulling the table
The similarity between this method and the traditional method is to determine the position of the first wall panel by the plug. The traditional positioning method of the second wall panel position is to determine the flexibility of the positioning mandrel, and the positioning method is no longer used. Mandrel positioning. This method measures the side consistency of the wall panel by pulling the table with the chassis end face (or lithographic end face) as a reference. Thereby ensuring the coaxiality of the holes. The advantage of this method is mainly to eliminate the influence of the positioning gap on the coaxiality, but it also puts special requirements on the wallboard and chassis:
(1) The distance from the side of the wall panel (referring to the pull surface) to the shaft hole is the same, which can be guaranteed by the single processing of the joint processing or machining center;
(2) The end face of the chassis should be perpendicular to the side or the centerline of the pre-made plug hole;
(3) The side of the wallboard is parallel to the shaft hole, and their positioning reference is the large plane of the wallboard during processing, which is also easy to do.
With this positioning method, the coaxiality error mainly comes from the perpendicularity error of the plug and the end face of the chassis; the consistency error of the pull shaft and the pull beam. For the convenience of calculation, the error of wall plate hole and side parallelism, the error of the plug feeler of the plug, the consistency error of the wall plate hole to the side, the flatness error of the chassis are neglected. At this time, the coaxiality error δ=0.00615 (the convolution error calculation formula is derived and the schematic diagram is omitted).
The calculation results show that the positioning method makes the coaxiality accuracy of the two wall panels greatly improved, and even improves the precision by more than one hundred times. Of course, there are quite a few error factors affecting the coaxiality, and some involve improvements in design and process, but this is undoubtedly a better assembly method for improving coaxiality.
In order to implement this positioning method, the design and process problems to be solved are as follows:
(1) When reading the table with the chassis as the reference, if the reading is changed within the thickness of the wallboard, the center reading of the wall thickness shall be taken as the standard;
(2) The multi-color printing machine has a long chassis, and the end surface of the chassis is far from the side of the wall plate. The groove perpendicular to the positioning surface can be processed on the chassis as a measurement reference (the printing machine without the chassis can be solved on the assembly plate) ;
(3) After a unit is positioned, the positioning of other units can be measured as the parallelism of the shaft holes, and the mandrel is measured with a special gauge caliper to obtain data for adjustment. In this way, it is possible to design a gauge with a direct gauge to measure the difference between the measured drive and the manipulated face distance.
3. Measures for positioning with double plugs
The two methods of positioning the wall panels described above are that one wall panel is positioned by the plug, and the other wall panel is oriented by the pull shaft and the pull beam. One method of positioning two panels is to use hole positioning, and the other method is to use the side panel of the wall panel to position the table. This two-way use of the anchor positioning method is to change the positioning of the pull table to the position of the plug. That is, when the printing machine chassis is machined, four cylindrical plug holes are pre-machined by the machining center, the cylindrical pin is pressed during assembly, and the contact condition is checked with a 0.02 mm feeler gauge. The accuracy of the coaxiality obtained by this method is lower than that of the pull-table measurement method, and the reason mainly depends on the positional accuracy of the four plug holes, and of course the consistency of the feeler gauge and the side of the wall panel. If the two groups of the plug have a degree of straightness of 0.05 and a feeler gauge of 0.02, it is inferred by the formula of the pull table method that the maximum value of the coaxiality error is about 0.1 mm. This positioning method is also more than ten times more accurate than the conventional positioning method.
4. Positioning method using laser collimator and centering light target
This method involves mounting the laser collimator in the hole in the wall panel and placing the light target in the hole in the other wall panel. When the red laser beam emitted by the laser collimator hits the light target, the positional deviation of the x and y axes is measured by four silicon photocells distributed in four quadrants at the center of the light target. When the wall panel is assembled, only the horizontal coaxiality is controlled, so the laser collimator can only be rotated by 180° in the horizontal plane. This method is to improve the direction of coaxiality accuracy. However, this method is inefficient and does not apply to assembly line production, but can be used for assembly accuracy calibration testing.
5. Measures for positioning in the coordinate inspection machine
The specification range of the three-coordinate inspection machine is very wide. For some small and medium-sized printing equipments, it can be positioned under the three-coordinate inspection machine, that is, some equipments with a facing aspect can also be assembled and positioned under the coordinate inspection machine. Of course, the cost is higher. A domestic company has already used this method for assembly positioning and other on-site inspections for key high-end printing equipment.
Fourth, the conclusion
The traditional wallboard positioning method has produced a large degree of coaxiality error, which is undoubtedly proved, in addition to the previous calculations, which are also proved in the assembly practice and user feedback.
The five assembly positioning methods proposed in this paper not only take into account the improvement of the current traditional positioning methods, but also propose specific measures to improve the accuracy of coaxiality and the direction of adopting advanced detection technology. These measures to improve the accuracy of the coaxiality are equally applicable to the overhaul of other printing machinery and printing equipment similar to the structure of the printing press.