1. Definition:
Parallel machine tools, also known as parallel structure machine tools and virtual axis machine tools, are also known as hexapod machine tools and hexapod machine tools. Parallel machine tool is developed on the basis of Stewart platform principle of spatial parallel mechanism, and it is a new concept machine tool that has just appeared in recent years. It is the product of the combination of parallel robot mechanism and machine tool, and it is a high-tech product which is highly combined with space mechanism, machinery manufacturing, numerical control technology, computer software and hardware technology and CAD/CAM technology. It overcomes the inherent defects of the traditional machine tool series mechanism, such as the cutter can only feed along the fixed guide rail, the freedom of cutter operation is low, and the flexibility and maneuverability of equipment processing are not enough. It can realize multi-coordinate linkage NC machining, assembly, measurement and other functions, and can better meet the processing of complex special parts. Since 1994 made its debut at Chicago Machine Tool Exhibition, it has been praised as "the machine tool of 265438+20th century" and has become the most vital new member of the machine tool family.
2. The characteristics of parallel machine tools
On the whole, the traditional serial mechanism machine tool belongs to the machine tool with simple mathematics and complex mechanism, while the parallel mechanism machine tool has simple mechanism and complex mathematics, and the movement of the whole platform involves quite a lot of mathematical operations, so the virtual axis parallel machine tool belongs to the knowledge-intensive mechanism. This new machine tool completely breaks the traditional concept of machine tool structure, abandons the tool guiding mode of fixed guide rail and adopts multi-bar parallel mechanism to drive, which greatly improves the rigidity of the machine tool and greatly improves the machining accuracy and quality. In addition, due to the improvement of its feed speed, it is easier to realize high-speed and ultra-high-speed machining. Because this machine tool has the advantages of high rigidity, high bearing capacity, high speed, high precision, light weight, simple mechanical structure, low manufacturing cost and high standardization, it has been successfully applied in many fields, so it has attracted widespread attention in academic circles. Series-parallel CNC machine tools composed of parallel and series not only have the advantages of parallel machine tools, but also have more practical value.
With the continuous development of high-speed cutting, the structural rigidity of the platform constructed by the traditional series mechanism and the high speed of the moving table have gradually become the bottleneck of technical development, and the parallel platform has become the best candidate. Compared with the series of machine tools, the parallel working platform has the following characteristics and advantages:
Simple structure and low price. The number of mechanical parts of the machine tool is greatly reduced compared with the platform with series structure, and it is mainly composed of ball screw, Hooke hinge, ball hinge, servo motor and other general parts. These general components can be produced by specialized manufacturers, so the manufacturing and inventory costs of this machine tool are much lower than those of traditional machine tools with the same function, and it is easy to assemble and carry.
High structural rigidity. Due to the closed-loop structure, it has the advantages of high stiffness and high speed, and its structural load streamline is short, while the tension and pressure of load decomposition are borne by six connecting rods at the same time. From the point of view of material mechanics, when the external force is constant, the stress and deformation of cantilever are the largest, followed by built-in and simply supported at both ends. Its stiffness-to-weight ratio is higher than that of traditional CNC machine tools.
High machining speed and low inertia. If the structural force changes direction (between tension and pressure), the two-force structure will be the most material-saving structure, and its moving parts are driven by six actuators at the same time, so the machine is easy to speed up and has low inertia.
And the machining accuracy is high. Because it is composed of multi-axis parallel mechanism, the lengths of six telescopic rods act on the position and attitude of the tool independently, so there is no accumulation and amplification of geometric errors of traditional machine tools (that is, serial machine tools), or even average effect; It has a thermal symmetrical structure design, so the thermal deformation is small; Therefore, it has the advantage of high precision.
Multifunctional and flexible. Because this machine tool is simple in mechanism and easy to control, it is easy to design a special machine tool according to the processing object. At the same time, it can also be developed into a general machine tool to realize milling, boring and grinding, and it can also be equipped with necessary measuring tools to form a measuring machine to realize the multi-function of the machine tool. This will bring huge application and market prospects, and it has a very broad application prospect in national defense and civil use.
Long service life. Because the stress structure is reasonable, the moving parts wear little, and there is no guide rail, there is no scratch, wear or corrosion caused by iron filings or coolant entering the guide rail.