Overview of platform positioning systems
time£º2011/3/30 click£º8037
Introduce each component one by one! To help readers better understand the positioning system, we will adopt the method of separate introduction, the whole system is broken down into each component to introduce one by one. We divide the positioning system into the following parts according to function:
1. Sliding track
2. Executor
3. Electric motor
4. Feedback device
5. Electronic drives and controllers
6. External device functionality
Direction control technology can be described as a variety of, and each has its own advantages and disadvantages. The following are some of them:
Kinematics
Kinematics design emphasizes the suppression of other excess degrees of freedom by carefully selecting single points of contact. If properly selected, each contact point of such a design can inhibit a degree of freedom. Therefore, five contact points will produce contact points with only one degree of freedom(6-5 = 1); If a system has six contact points at the same time, the system will be in an unbalanced state. In most cases, kinematics design requires the application of forces(gravity, magnetism, vacuum, or spring forces) to keep all points in contact; In addition, if the ball is used as the contact point, the sliding friction force will be replaced by rolling friction force. Although such designs are "pure" in accordance with mechanical principles, their load capacity is low due to fewer contact points. Among all design methods, kinematics design is a more extreme design, while the other extreme design is an average area design(for example, a dovetail slide-see below). By comparing the kinematics and the "elastic average" method, it is helpful to find a relatively ideal design method. Kinematics design can basically reproduce the geometry of the moving surface(usually composed of planes and/or cylinders). For example, this method does not transmit stress due to thermal expansion. However, it is unavoidable that these advantages will be plagued by low natural frequency, low rigidity, and low load capacity.
Swallowtail slider
Swallowtail sliding track and kinematics design can form a sharp contrast; This design method does not only select a few contact points, but also depends on a very large contact area to improve stiffness and load capacity. This kind of moving surface usually needs to be "polished" to obtain a higher surface flatness, and the tail-end method can improve the stability of the surface moving parts during the movement. The tailtail method is usually used for the design of machining tools because such machinery requires high load capacity. Compared with the rolling mode, the sliding mode will significantly increase the friction force. Since the parts will wear during sliding, most designs contain adjustable preloads or reinforcement devices to reduce friction. Although the quality of the dovetail method is usually larger, it is generally made of cast iron and is relatively rigid, similar to the material of the sliding track itself. Therefore, the natural frequency of the overall component of the sliding track is increased, which is very critical for high-speed milling and planer operation.
Cross-cylindrical ball slide
The structure of the cross-cylindrical ball slide track is in & amp; Quot; V& Quot; A cylindrical ball is placed in the zigzag track. The rotation angle of every other ball is 90 degrees, forming a symmetrical load capacity. Due to Ball & & Quot; V& Quot; The zigzag tracks are in direct contact, thus providing a load capability that is one level higher than that of the spherical slider Gaochu. The retaining force and preloading of the ball are similar to those of the spherical sliding track. The cross ball design provides medium uniform friction, high load energy, high linear and torsional stiffness, medium cost and very good linear accuracy.
The line contact characteristics of the cross ball slider are weaker than those of the spherical slider. Therefore, the latter is more suitable for use in environments where there is a fine grinding foreign body(such as grinding operations). Compared with the spherical ball slider, the friction force of the cylindrical ball is relatively large, but due to the relatively average characteristics of the line contact, the volatility of the friction force is reduced.
Ball slider
The term "ball" in this article refers to a slider assembly. It includes a hardened track and three or more casters or cam slave mechanisms. These are mainly used to define the direction of motion of the moving component and the movement itself. Examples include squares with six slave cams(of which two pairs are located on two different sides and the other two spring slave wheels on the other two sides), four-sided sliders, and double & amp with three or more conjugate rollers; Quot; V& Quot; A zigzag slider. Since circular components are not used, this type of design incorporates the compact design and mobility characteristics of circular components. In the actual operation of this structure, the ball in it will still be reused, but the preloading force will always exist during its reuse. This avoids the problem of friction fluctuation of traditional cycle components. Usually the sliding block has lower cost, lower or moderate load capacity, low friction and uniformity, and the accuracy of the straight line movement is as good as that of the sliding block using the roller.
Twisted.
Torsion is a slider technique that is often overlooked. They use the elasticity of the parts themselves to define the motion of the linear flat axis. A more common example is the use of two thin metal sheets with photolithography threads to connect the inner and outer diameters. The speaker uses a tickling slider to define the axis of motion of the sound coil. Another common design is the parallelogram deflection slider. For some applications with limited trips, flexural sliders will be a compact and economical slider technique. In addition to the highly stable movement characteristics and no rotating parts, the flexural slider can be used as a linear transmitter to amplify or reduce the input motion. A flexural slider with a fairly high magnification resolution can be purchased on the market. Only a simple micro-separation can be used to obtain repeatable Egyptian unit level movement.
2. Executor
By selecting the appropriate guide rail to set a certain freedom of movement, we can then start to solve another independent problem, that is, how to generate incremental motion along the guide rail. We call the device that can generate motion the actuator. First of all, it is necessary to distinguish between an executor that can select one of two positions along the direction of motion and an executor that can be programmed to select one position from multiple positions. The common devices in the former type of actuator are electromagnetic valves and bar/hydraulic cylinders. In general, if the application requires that only one of the two positions be repeatedly positioned, it is usually more economical to use a "digital" executor than to use a full-featured, CPU-based functional positioning system. But that is not good news for manufacturers like us who specialize in "outlandish" positioning systems.
A. Double bit executor
Electromagnetic valve
The electromagnetic valve is a compact, low-cost actuator. If it is used together with a good guide rail, a momentum absorber, and a high hardness brake, it can provide high repeatability and fast two-position positioning functions. It mainly depends on the mutual attraction between the soft core as a moving part and the gradient electromagnetic field generated by the coil. Because it is difficult to generate a high gradient magnetic field at a long distance, the electromagnetic valve is limited to the application of a relatively short stroke(usually 1 cm). Based on the electromagnetic valve, the design of the ring heating, AC induction vibration or click sound and electromagnetic suction has a strong non-linear.
cylinder
A gas cylinder or hydraulic cylinder can provide low-cost, high-force, high-speed two-position motion performance. Although they have become larger and larger as the journey increases, there are now "fewer rods" cylinders, and they are designed to be compact and similar to circular slides. When used with a more complex servo proportional valve and feedback device, the cylinder can also be programmed to locate multiple locations.
cam
The cam has a variety of dual position indexing functions, especially when reciprocating. Automobile suction and exhaust valves may be common applications. Although they use the principle of sliding friction(the surface is easy to wear), the internal combustion engine cam actuator can still work reliably and accurately, and can achieve no-fault operation. The average number of daily operation of the exhaust pipe is as high as 1 million times! Cam positioning limited to line
Linear motor