Application of Virtual Prototype Technology in Printing Machinery Design
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With the integration of the global economy, the competition in the printing machinery product market has become increasingly fierce. In order to improve market competitiveness, it is necessary to continuously shorten the research and development cycle of new products, improve product quality, performance, and reduce development costs. Under this demand, the computer technology represented by virtual prototyping technology is developing continuously and is a new modern design method. Using virtual design methods, you can design, analyze, and evaluate product performance at the beginning of product design, identify and optimize physical prototype parameters, thereby reducing development risk of new products, shortening development cycles, and improving product performance. This paper takes the specific design of printing machinery as an example to illustrate the application of virtual prototyping technology in the field of printing machinery design.
In the traditional printing machinery design process, engineers first select the model according to the needs of machine function improvement, then calculate the results, draw the mechanical parts drawing, component drawing and assembly drawing, and then hand it to the workshop for trial production. After the sample is out, run the test on the sample, compare the actual results of the test with the theoretical concept before design, find the cause of the difference, and then re-design the design until the sample meets the needs of improvement. This design process requires a long period of time and high sample trial cost, which often fails to meet the market requirements for the timeliness of new machine replacement, and brings huge waste of manpower and material resources. Therefore, it is necessary to use modern design methods, namely virtual prototype technology, to improve the design method of printing machinery.
What is virtual prototyping technology? Virtual prototyping technology in mechanical engineering, also known as mechanical system dynamic simulation technology, is a computer-aided engineering (CAE) technology developed rapidly in the 1980s with the development of computer technology. The engineer builds a prototype model on the computer, performs various dynamic performance analysis on the model, then improves the prototype design and replaces the traditional physical prototype experiment with a digital form. The use of virtual prototyping technology can greatly simplify the design and development process of mechanical products, greatly shorten the product development cycle, significantly reduce product development costs and costs, significantly improve product quality, improve system-level performance of products, and obtain optimized and innovative design products. . Therefore, as soon as this technology emerged, it was immediately taken seriously by industrialized countries, relevant scientific research institutions, universities and companies. Many famous manufacturers have introduced virtual prototype technology into their respective product developments and achieved good economic benefits. According to the statistics and predictions of international authoritative personnel on product performance experiments and research and development methods in the field of mechanical engineering, traditional mechanical system physical experimental research methods will be replaced by computerized digital simulation technology that will be rapidly developed. The research scope of virtual prototype technology is mainly the kinematics and dynamics analysis of mechanical systems. The core of it is the use of computer-aided analysis technology to analyze the kinematics and mechanics of mechanical systems to determine the force required for the movement of the system and its components. Reaction force.
This article takes the specific equipment R&D as an example to discuss the application of the advanced technology of virtual prototype in practical engineering and practical work, to explore the steps and methods of virtual prototyping technology used in the design of printing machinery.
As is well known, die-cutting machines are important post-press surface finishing processing equipment in the packaging printing industry. After the die-cutting, the printed products can greatly improve the grade and play an important role in increasing the added value of the product packaging. The automatic flat die-cutting machine is generally composed of a paper feeding portion, a die-cutting hot stamping portion, a stripping portion, and a take-up stacking portion as shown in FIG.
Figure 1 Automatic flat die cutting machine
At present, the working speed of foreign automatic die-cutting machines is generally between 7500 and 9000 sheets/hour. Compared with this, the automatic flat die-cutting machine produced in China has a lower working speed, generally up to 5500-7500 sheets/hour. In terms of die cutting precision, the die cutting precision of foreign automatic flat die cutting machine can usually be controlled at about 0.10mm, while the die cutting precision of domestic automatic flat die cutting machine is in the range of 0.15~0.20mm, only a small number of models Can achieve a die cutting precision of 0.1mm. Moreover, when the working speed of the domestic automatic flat die cutting machine is high, the die cutting precision will be greatly reduced, which seriously affects the die cutting quality of the printed product.
After careful research on the existing die-cutting machines in China, including some foreign die-cutting machines, the author found that after the speed-cutting of the die-cutting machine, a very important factor that restricts the precision of die-cutting is the insufficient time for paper positioning. We analyze this, the principle of paper positioning and conveying mechanism of die-cutting machines at home and abroad is basically the same. As shown in Figure 2.
Figure 2 Die-cutting machine paper positioning and conveying mechanism
The working process of the positioning and conveying mechanism is that the large sprocket drives the chain (divided into segments of equal length) to make periodic intermittent movements in the direction of molding. When the paper carried by the current chain is in the molding state, the latter chain also reaches the paper picking point (point A). At this point, the large sprocket and the chain are stationary. At this time, the swinging plate is horizontally placed, the paper is conveyed along the swinging plate, and is positioned by a gauge device fixed to the swinging plate, and then delivered to the bite on the chain. After the handover is completed, the swinging plate is hem. The paper carried by the current chain completes the molding work. When the large sprocket is driven to move forward, the newly acquired paper chain will move and reach the molding position, and the cycle will resume.
From a certain chain to point A, starting to pick up the paper, and then starting to leave point A, the time used is usually only 2/5 of a cycle. This 2/5 time contains the paper positioning time. And, these 2/5 times are not all used for paper positioning. In order not to interfere with the mechanism, after the chain reaches point A, the oscillating plate can swing up; the oscillating plate must be hem before the chain moves away from point A, plus the stabilization time of the rule, etc., the time used for paper positioning. Generally less than half of this 2/5 time. It can be seen that the paper positioning time is originally very tight, and as the speed of the machine continues to increase, the absolute time of paper positioning becomes shorter and shorter. Undoubtedly, the lack of positioning time will cause great damage to the die cutting precision.
To this end, an improved method has been proposed to obtain a new paper positioning and conveying mechanism that will greatly improve the positioning time of the paper. As shown in Figure 3.
Figure 3 Improved paper positioning and transport mechanism
The new agency abandoned the original swinging plate and installed a transfer nozzle. After the paper is positioned at point B, it is handed over to the paper feed nozzle; the paper feed nozzle is horizontally moved, handed over to the paper take-up chain, and then the hem returns. The control of the air flow and the trajectory movement of the transfer nozzle can be done by the cam mechanism, which is very easy to implement.
The difference between the new mechanism and the original mechanism is that the original paper positioning is subject to the chain drive system. It must wait until the paper take-up chain reaches point A to swing the plate to the horizontal position, and then the paper comes over and starts to position. The improved positioning of the paper is relatively independent. It can start the positioning of the paper before the picking chain has reached the point A, and it can be handed over before the picking chain leaves point A. The time for paper positioning is greatly extended.
For each cycle of the transfer system, the rest of the time can be used to position the paper except for the paper feed and return of the transfer nozzle. Obviously, after the improvement, the paper positioning time is longer than the original mechanism at low speed even if it is speeding up.
After the clear design scheme, according to the process requirements of the die-cutting machine, the mechanism selection is carried out, and the cam-link mechanism is taken as the preliminary design scheme through analysis and comparison. The modified trapezoidal acceleration law is selected as the follower motion law, the mechanism parameters are determined, the design calculation is performed, and the SOLIDWORKS software entity modeling is adopted. Because of the relationship between the lengths, the basis for the calculation and the detailed process are not introduced here. According to the basic method of mechanical design, it is relatively easy to find the theoretical model.
The key to the question now is, can the requirements be met for the designed product? Different from the traditional design method, there is no need to rush to the workshop to process parts according to the drawings, but to adopt a new method, that is, to use virtual prototype technology to verify whether the designed samples meet the needs of use. Here we need to use the ADAMS software. ADAMS software is a mechanical system dynamics simulation analysis software developed by MDI Company of the United States. It can be used to predict the performance of mechanical systems, range of motion, collision detection, peak load and input load of finite element calculation. It uses an interactive graphical environment and parts library, constraint library, force library, and a fully parameterized mechanical system geometry model to perform static, kinematic, and dynamic analysis of the virtual prototype system, outputting displacement, velocity, acceleration, and reaction curve. Figure 4 shows the working interface of the virtual prototyping software ADAMS.
Figure 4 Virtual Prototyping Software ADAMS
Under the ADAMS interface, geometric modeling can be performed directly, and ADAMS has a rich set of geometric modeling tools. If you use other specialized modeling tools, it is much more convenient to import them into ADAMS after building the model. Therefore, we modeled the design drawings by SOLIDWORKS, imported them into ADAMS, and completed the following work in sequence, and then simulated and tested with ADAMS.
1 add constraints, such as hinge pairs, cylindrical pairs, etc.;
2 set the physical properties of the mechanism, such as materials;
3 Perform simulation calculation analysis, set output mode, etc.
After introducing the newly designed die-cutting machine to the ADAMS, the actual performance of the designed product is directly obtained according to the kinematics, dynamics and elastic dynamics analysis of the mechanism. Here, the mechanism of the specific application of the mechanism is illustrated by taking the elastic dynamic analysis process of the mechanism as an example.
The development trend of die-cutting machines is that the speed of the machine is constantly increasing, and the weight of the machine tends to be reduced. Therefore, in the design of the mechanism, it should be considered that as the weight of the machine is reduced, the flexibility of the member is increased, and the flexible member is deformed by the external force and the inertial force, thereby causing the real movement of the mechanism and the expected movement. An error has occurred. As the speed increases, the inertial force increases sharply, and the problem becomes more prominent. Therefore, an elastic dynamic analysis of the new mechanism must be performed to verify that the mechanism can meet the accuracy requirements at high speeds.
The first step: Considering that the connecting rod is relatively strong, it is also an important part of the upper and lower parts of the connecting mechanism. Its flexible change will have a great influence on the accuracy of the mechanism. Therefore, consider the flexible body of the connecting rod (machine speed selection) Set to 9000 rev / h).
Figure 5: Flexible body parts
The second step: the flexible body is loaded into the mechanism to replace the original rigid body part, the other parts remain unchanged, the assembly is re-assembled, the motion simulation of the mechanism is performed, and the displacement curve of the transfer paper is output.
Figure 6 Flexible body loading mechanism
The third step: comparing the displacement curve of the transfer paper before the replacement, and outputting the difference curve of the two with time.
Figure 7 Displacement error results
From the results in Figure 7, it can be seen that even in the case of high speed (9000 rev / h), the error of the mechanism is in a small range, the maximum is 0.01mm, far less than the 0.10mm error of the machine, to meet the design. Claim.
As mentioned above, this paper makes a structurally innovative design of the die-cutting machine in the printing machine. After designing the theoretical data, the sample is not sampled according to the traditional method, but the virtual prototype analysis software ADAMS is used to carry out the mechanism. Kinematics, dynamics, and elastic dynamics analysis show that the designed mechanism meets the design requirements. In this way, the design process is greatly simplified, the design cycle is shortened, and the design work of the printing machine is greatly facilitated. Therefore, in the design of printing machinery, mastering the application of virtual prototyping technology is an urgent requirement of new technology for engineers.