Design of Shenzhen Double Ten Precision Machinery System
    With the development of science and technology and industrial production, the function and accuracy of precision machinery and instruments have also become higher and higher.
 Requirements. At present, the positioning tip or transmission accuracy of the worktable is generally required to be 0. lium, and the spindle rotation accuracy is
0. O1um. The indexing accuracy is about 0.2s. Functionally, it is required to be able to detect points, lines, and even spatial surfaces, and automatically collect and
 Processing data and real-time online monitoring and control. To achieve these requirements. Relying only on traditional methods, only focusing on improving
 The accuracy and functions of the mechanism itself are not only poor in economic efficiency, but sometimes difficult to achieve. Therefore, most modern precision machinery uses electricity
 Comprehensive technologies such as sub-computers, optics, electrical, hydraulics, and mechanics can meet the requirements of high precision, high efficiency and multiple functions.
    This chapter will give an overall description of the precision mechanical system, focusing on those parts that have a greater impact on the accuracy and performance of the system.
 Parts. Such as base, support, worktable, spindle and servo mechanical system. Since there are specialized courses in optics and computer technology, this book
 No longer.
 Base and support
 1. The structural characteristics and main technical requirements of the base and support
    Precision mechanical instruments have a variety of bases and supports. They not only connect and support various parts and components.
 The role of position, but also to ensure the accuracy of the instrument.
    As shown in Figure 3-1, the camera is repeated step by step. It can be seen from the figure that the base and the body support
 The precision workbench, laser interferometry system and column. The column supports the camera system. The camera objective lens can be moved up and down along the column guide for focusing. After removing the hood, you can see that the workbench, various transmission elements and interferometer brackets are supported on the fuselage (see Figure 3-2)
     It can be seen from the figure that the characteristics of the base and support are:
     1. Larger size, it is the basic support of the whole instrument. Not only its own weight is large, but also the main external load is bearing;
     2. The structure is more complicated. There are many machining surfaces (or holes). And the mutual position accuracy and the accuracy of itself are high.
    According to the above characteristics, special attention should be paid to rigidity, thermal deformation, accuracy, vibration resistance and structural manufacturability when designing.
     (1) Rigidity
    The body of the above-mentioned step-by-step camera is not only heavier, but also because of the workbench and column on the body, there is a camera on the stand.
 The head, so some component loads are directly or indirectly acting on the fuselage and the column. As the moving parts move, the load condition
 The situation will change. In this case, to ensure that the elastic deformation of the base and the column is within the allowable range, it must be
 Have sufficiently high stiffness. If the stiffness of the designed part is insufficient, the resulting geometric and positional deviation may be greater than the manufacturing error
 difference.
    Stiffness not only affects the degree of emotion, but also has a direct relationship with the natural frequency, which is of great significance to the improvement of dynamic performance.
    The stiffness is divided into static stiffness and dynamic stiffness according to the nature of the load.
     (2) Vibration resistance
    The vibration resistance of the support is its ability to resist forced vibration. The source of vibration may be inside the instrument. For example, the unbalance of the driving motor rotor or rotating parts; the commutation impact of reciprocating parts. The vibration source may also be external to the instrument. Such as machinery, vehicles, and personnel activities. And the ventilators and refrigerators in the constant temperature room. When the base is affected by the vibration source to produce vibration, in addition to the vibration and shaking of the entire instrument, the main related parts and components may also produce
 Bending or torsional vibration. The shaking and vibration of the whole machine generally does not affect the work. However, the vibration of parts or parts may affect the accuracy of the instrument.
 Make an impact. When the frequency of the vibration source coincides with the natural frequency of the component or is an integral multiple of it, resonance will occur, which may make the instrument unable to
 Normal work, reduce use accuracy and shorten service life. Therefore, the amplitude of vibration, especially the relative amplitude, is specified
 allowance. For example, a light wave interferometer aperture measuring instrument (with an accuracy of 0.03mm), when the excitation frequency is 35Hz, the worktable is allowed to be in the vertical direction
 The amplitude of the direction is 0.12um; the horizontal direction is 0.22um. For CMMs, some foreign products usually stipulate the excitation frequency
 Rate is below 50H. The amplitude must not exceed Sum. When the amplitude exceeds the specified allowable value, in order to improve the vibration resistance, the following three methods are often used
 Start to improve:
     1. Improve static rigidity: reasonably design the cross-sectional shape and size of the component. Reasonable arrangement of ribs or partitions can improve static rigidity and
 High natural frequency to avoid resonance;
     2. Increase the damping: increasing the damping has a great effect on improving the stiffness, the resistance of the hydrodynamic or static pressure guide rail, the gas static pressure guide rail
 The damping of the Nibi rolling guide is large;
     3. Reduce weight: reduce the weight without reducing the stiffness of the component, which can increase the natural frequency. To thin the wall appropriately
 Thick, using steel welded structure, etc.
    Sometimes vibration isolation measures are taken to reduce the influence of external vibration sources on the normal operation of the instrument. Currently commonly used vibration isolation materials are: Gundam
 Spring, rubber, foam latex. In addition, air cushion vibration can also be used.
    (3) Stability
    The structure of the base and the support is relatively complicated, and the internal stress is easily generated due to the uneven cooling rate at various places during casting. This
 This kind of internal stress is the main reason for the long-term instability of the part size. Therefore, the base and support must be aged to eliminate
 In addition to internal stress, reduce deformation.
    There are two aging treatment methods, namely natural aging and artificial aging.
    1. Natural aging treatment: Place the casting blank or the semi-finished product after rough processing naturally in the open place, after several months
 Even within a few years, its internal stress gradually "relaxed", and gradually deformed during the process of internal stress elimination, until the shape stabilizes.
 Processing after setting, according to experience, the natural aging time is generally 1 month to 6 months, the length of time depends on the base or support
 A series of factors such as the size, shape and structure, casting conditions and final accuracy requirements. Large instruments and high-precision components
 The aging treatment takes a long time. The natural aging method is simple and the effect is better, but it covers a large area, has a long period, and has a backlog of funds.
    2. Artificial aging treatment: the most commonly used is heat treatment. Hang the casting flatly on the baking sheet, so that the surroundings are evenly heated
 Even. Choose different temperature change speeds according to the actual situation. Figure 3-3 is an example, the temperature rises at 60t per hour at the beginning
 The speed is heated to 530-55010, kept for 4-6h, and then cooled with Shanghai. The instrument components of general precision undergo an aging treatment,
 Can meet the requirements. High-precision components need to undergo multiple aging treatments before finishing.
     (4) Thermal deformation
    For machinery and instruments with high precision requirements, thermal deformation has become an important factor causing errors. For example, crashes
 When there is a temperature difference between the guide rail surface and the bottom surface of the body, the guide rail surface will produce concave or convex in the vertical plane (Figure 3-4), the maximum concave and convex
‘It can be obtained as follows:
It can be seen that the error caused by thermal deformation is very large.
    Due to the different sizes, shapes, and structures of the whole machine and various parts, the time to reach thermal equilibrium is also different, and the components thermally expand
 The speed is related to the size of the heat capacity.
    Measure the base and support of a universal involute tooth profiler, and get the curve shown in Figure 3-5. The bracket temperature with the smallest heat capacity
 When the change curve 2 passes for a period of time, the I division and the room temperature curve 3 remain equidistant and reach equilibrium. Temperature change curve of base with large heat capacity]
 It has been in the process of heating up. In a constant temperature environment, after 15 hours, the components of the instrument have not yet reached the temperature equilibrium state. From Beike
 It is known that if various parts are deformed, the thermal deformation has not reached a stable state.} It will affect the accuracy of the instrument. Therefore, it is necessary to take measures to control the temperature within a certain range.
    I. Strictly control the temperature of the working environment
    According to the accuracy requirements of the instrument, different requirements are put forward for the ambient temperature. In a general constant temperature room, filtered air flows in from the ceiling
 Indoors, exhaust from near the floor. When the air passes the light source, the heat will be taken down from near the ceiling and the room temperature will rise.
 If the temperature of the incoming air is lowered below the required temperature (e.g. the low temperature is generally below 20'C), it will cause a part of the cold
 The air sinks to the floor, causing the upper and lower temperature "stratification". For higher large instruments, this kind of indoor temperature stratification is very important for accuracy.
 The impact cannot be ignored. A better constant temperature room should be air intake from the side or the floor, and exhaust air from the upper plate. The advantages of this approach are
The air of 201C temperature flows directly into the room from the floor and exhausts from the ceiling. The heat of the light source is also exposed from the ceiling. For requirements
 For instruments with small temperature fluctuations (such as laser measuring instruments), it is necessary to adopt the method of "room in room" and hierarchical control of room temperature. For example,
 The temperature of the thermostatic chamber is controlled at ±1°C. An additional protective cover is added to the indoor instrument, and the temperature in the cover is controlled at ±0.15°C. Advanced abroad
 The environmental temperature control technology has reached a very high level, and the temperature in some laboratories in the United States can reach 20 ± 0.00561c.
     2. Control the heat transfer of the heat source inside the instrument
    Measures must also be taken to control the heat transfer of the thermal image of the instrument's own motor, lighting, etc.
     (D uses cold light sources (such as light-emitting diodes);
     (2) Separate or separate the heat source;
     (3) For heat sources that cannot be separated and are inconvenient to separate, such as bearings, screw nut pairs, etc., measures must be taken to reduce
 Heat generation,
    (4) Wait for the temperature of the instrument to balance before starting to work.