基于PLC控制的三自由度氣動機械手設計,基于,plc,控制,節(jié)制,自由度,氣動,機械手,設計 文 獻 翻 譯 機械學院 Robot After more than 40 years of development, since its first appearance till now, the robot has already been widely applied in every industrial fields, and it has become the important standard of industry modernization. Robotics is the comprehensive technologies that combine with mechanics, electronics, informatics and automatic control theory. The level of the robotic technology has already been regarded as the standard of weighing a national modern electronic-mechanical manufacturing technology. Over the past two decades, the robot has been introduced into industry to perform many monotonous and often unsafe operations. Because robots can perform certain basic more quickly and accurately than humans, they are being increasingly used in various manufacturing industries. With the maturation and broad application of net technology, the remote control technology of robot based on net becomes more and more popular in modern society. It employs the net resources in modern society which are already three to implement the operatio of robot over distance. It also creates many of new fields, such as remote experiment, remote surgery, and remote amusement. What's more, in industry, it can have a beneficial impact upon the conversion of manufacturing means. The key words are reprogrammable and multipurpose because most single-purpose machines do not meet these two requirements. The term “reprogrammable” implies two things: The robot operates according to a written program, and this program can be rewritten to accommodate a variety of manufacturing tasks. The term “multipurpose” means that the robot can perform many different functions, depending on the program and tooling currently in use. Developed from actuating mechanism, industrial robot can imitation some actions and functions of human being, which can be used to moving all kinds of material components tools and so on, executing mission by execuatable program multifunction manipulator. It is extensive used in industry and agriculture production, astronavigation and military engineering. During the practical application of the industrial robot, the working efficiency and quality are important index of weighing the performance of the robot. It becomes key problems which need solving badly to raise the working efficiencies and reduce errors of industrial robot in operating actually. Time-optimal trajectory planning of robot is that optimize the path of robot according to performance guideline of minimum time of robot under all kinds of physical constraints, which can make the motion time of robot hand minimum between two points or along the special path. The purpose and practical meaning of this research lie enhance the work efficiency of robot. Due to its important role in theory and application, the motion planning of industrial robot has been given enough attention by researchers in the world. Many researchers have been investigated on the path planning for various objectives such as minimum time, minimum energy, and obstacle avoidance. The basic terminology of robotic systems is introduced in the following: A robot is a reprogrammable, multifunctional manipulator designed to move parts, materials, tools, or special devices through variable programmed motions for the performance of a variety of different task. This basic definition leads to other definitions, presented in the following paragraphs that give a complete picture of a robotic system. Preprogrammed locations are paths that the robot must follow to accomplish work. At some of these locations, the robot will stop and perform some operation, such as assembly of parts, spray painting, or welding. These preprogrammed locations are stored in the robot’s memory and are recalled later for continuous operation. Furthermore, these preprogrammed locations, as well as other programming feature, an industrial robot is very much like a computer, where data can be stored and later recalled and edited. The manipulator is the arm of the robot. It allows the robot to bend, reach, and twist. This movement is provided by the manipulator’s axes, also called the degrees of freedom of the robot. A robot can have from 3 to 16 axes. The term degrees of freedom will always relate to the number of axes found on a robot. The tooling and grippers are not part of the robotic system itself: rather, they are attachments that fit on the end of the robot’s arm. These attachments connected to the end of the robot’s arm allow the robot to lift parts, spot-weld, paint, arc-well, drill, deburr, and do a variety of tasks, depending on what is required of the robot. The robotic system can also control the work cell of the operating robot. The work cell of the robot is the total environment in which the robot must perform its task. Included within this cell may be the controller, the robot manipulator, a work table, safety features, or a conveyor. All the equipment that is required in order for the robot to do its job is included in the work cell. In addition, signals from outside devices can communicate with the robot in order to tell the robot when it should assemble parts, pick up parts, or unload parts to a conveyor. The robotic system has three basic components: the manipulator, the controller, and the power source. Manipulator The manipulator, which dose the physical work of the robotic system, consists of two sections: the mechanical section and the attached appendage. The manipulator also has a base to which the appendages are attached. The base of the manipulator is usually fixed to the floor of the work area. Sometimes, though, the base may be movable. In this case, the base is attached to either a rail or a track, allowing the manipulator to be moved from one location to anther. As mentioned previously, the appendage extends from the base of the robot. The appendage is the arm of the robot. It can be either a straight, movable arm or a jointed arm. The jointed arm is also known as an articulated arm. The appendages of the robot manipulator give the manipulator its various axes of motion. These axes are attached to a fixed base, which, in turn, is secured to a mounting. This mounting ensures that the manipulator will remain in one location. At the end of the arm, a wrist is connected. The wrist is made up of additional axes and a wrist flange. The wrist flange allows the robot user to connect different tooling to the wrist for different jobs. The manipulator’s axes allow it to perform work within a certain area. This area is called the work cell of the robot, and its size corresponds to the size of the manipulator. As the robot’s physical size increases, the size of the work cell must also increase. The movement of the manipulator is controlled by actuators, or drive system. The actuator, or drive system, allows the various axes to move within the work cell. The drive system can use electric, hydraulic, or pneumatic power. The energy developed by the drive system is converted to mechanical power by various mechanical drive systems. The drive systems are coupled through mechanical linkages. These linkages, in turn, drive the different axes of the robot. The mechanical linkages may be composed of chains, gears, and ball screws. Controller The controller in the robotic system is the heart of the operation. The controller stores preprogrammed information for later recall, controls peripheral devices, and communicates with computers within the plant for constant updates in production. The controller is used to control the robot manipulator’s movements as well as to control peripheral components within the work cell. The user can program the movements of the manipulator into the controller through the use of a hand-held teach pendant. This information is stored in the memory of the controller for later recall. The controller stores all program data for the robotic system. It can store several different programs, and any of these programs can be edited. The controller is also required to communicate with peripheral equipment within the work cell. For example, the controller has an input line that identifies when a machining operation is completed. When the machine cycle is completed, the input line turns on, telling the controller to position the manipulator so that it can pick up the finished part. Then, a new part is picked up by the manipulator and placed into the machine. Next, the controller signals the machine to start operation. The controller can be made from mechanically operated drums that step through a sequence of events. This type of controller operates with a very simple robotic system. The controllers found on the majority of robotic systems are more complex devices and represent state-of-the-art electronics. This is, they are microprocessor-operated. These microprocessors are either 8-bit, 16-bit, or 32-bit processors. This power allows the controller to the very flexible in its operation. The controller can send electric signals over communication lines that allow it to talk with the various axes of the manipulator. This two-way communication between the robot manipulator and the controller maintains a constant update of the location and the operation of the system. The controller also controls any tooling placed on the end of the robot’s wrist. The controller also has the job of communicating with the different plant computers. The communication link establishes the robot as part of a computer-assisted manufacturing (CAM) system. As the basic definition stated, the robot is a reprogrammable, multifunctional manipulator. Therefore, the controller must contain some type of memory storage. The microprocessor-based systems operate in conjunction with solid-state memory devices. These memory devices may be magnetic bubbles, random-access memory, floppy disks, or magnetic tape. Each memory storage device stores program information for later recall or for editing. Power supply The power supply is the unit that supplies power to the controller and the manipulator. Two types of power are delivered to the robotic system. One type of power is the AC power for operation of the controller. The other type of power is used for driving the various axes of the manipulator. For example, if the robot manipulator is controlled by hydraulic or pneumatic drives, control signals are sent to these devices, causing motion of the robot. For each robotic system, power is required to operate the manipulator. This power can be developed from either a hydraulic power source, a pneumatic power source, or an electric power source. These power sources are part of the total components of the robotic work cell. Classification of Robots Industrial robots vary widely in size, shape, number of axes, degrees of freedom, and design configuration. Each factor influences the dimensions of the robot’s working envelope or the volume of space within which it can move and perform its designated task. A broader classification of robots can been described as blew. Fixed and Variable-Sequence Robots. The fixed-sequence robot (also called a pick-and place robot) is programmed for a specific sequence of operations. Its movements are from point to point, and the cycle is repeated continuously. The variable-sequence robot can be programmed for a specific sequence of operations but can be reprogrammed to perform another sequence of operation. Playback Robot. An operator leads or walks the playback robot and its end effector through the desired path. The robot memorizes and records the path and sequence of motions and can repeat them continually without any further action or guidance by the operator. Numerically Controlled Robot. The numerically controlled robot is programmed and operated much like a numerically controlled machine. The robot is servo-controlled by digital data, and its sequence of movements can be changed with relative ease. Intelligent Robot. The intellingent robot is capable of performing some of the functions and tasks carried out by human beings. It is equipped with a variety of sensors with visual and tactile capabilities. Robot Applications The robot is a very special type of production tool; as a result, the applications in which robots are used are quite broad. These applications can be grouped into three categories: material processing, material handling and assembly. In material processing, robots use to process the raw material. For example, the robot tools could include a drill and the robot would be able to perform drilling operations on raw material. Material handling consists of the loading, unloading, and transferring of workpieces in manufacturing facilities. These operations can be performed reliably and repeatedly with robots, thereby improving quality and reducing scrap losses. Assembly is another large application area for using robotics. An automatic assembly system can incorporate automatic testing, robot automation and mechanical handling for reducing labor costs, increasing output and eliminating manual handling concerns. Hydraulic System There are only three basic methods of transmitting power: electrical, mechanical, and fluid power. Most applications actually use a combination of the three methods to obtain the most efficient overall system. To properly determine which principle method to use, it is important to know the salient features of each type. For example, fluid systems can transmit power more economically over greater distances than can mechanical type. However, fluid systems are restricted to shorter distances than are electrical systems. Hydraulic power transmission systems are concerned with the generation, modulation, and control of pressure and flow, and in general such systems include: 1. Pumps which convert available power from the prime mover to hydraulic power at the actuator. 2. Valves which control the direction of pump-flow, the level of power produced, and the amount of fluid-flow to the actuators. The power level is determined by controlling both the flow and pressure level. 3. Actuators which convert hydraulic power to usable mechanical power output at the point required. 4. The medium, which is a liquid, provides rigid transmission and control as well as lubrication of components, sealing in valves, and cooling of the system. 5. Connectors which link the various system components, provide power conductors for the fluid under pressure, and fluid flow return to tank(reservoir). 6. Fluid storage and conditioning equipment which ensure sufficient quality and quantity as well as cooling of the fluid.. Hydraulic systems are used in industrial applications such as stamping presses, steel mills, and general manufacturing, agricultural machines, mining industry, aviation, space technology, deep-sea exploration, transportation, marine technology, and offshore gas and petroleum exploration. In short, very few people get through a day of their lives without somehow benefiting from the technology of hydraulics. The secret of hydraulic system’s success and widespread use is its versatility and manageability. Fluid power is not hindered by the geometry of the machine as is the case in mechanical systems. Also, power can be transmitted in almost limitless quantities because fluid systems are not so limited by the physical limitations of materials as are the electrical systems. For example, the performance of an electromagnet is limited by the saturation limit of steel. On the other hand, the power limit of fluid systems is limited only by the strength capacity of the material. Industry is going to depend more and more on automation in order to increase productivity. This includes remote and direct control of production operations, manufacturing processes, and materials handling. Fluid power is the muscle of automation because of advantages in the following four major categories. 1. Ease and accuracy of control. By the use of simple levers and push buttons, the operator of a fluid power system can readily start, stop, speed up or slow down, and position forces which provide any desired horsepower with tolerances as precise as one ten-thousandth of an inch. Fig. shows a fluid power system which allows an aircraft pilot to raise and lower his landing gear. When the pilot moves a small control valve in one direction, oil under pressure flows to one end of the cylinder to lower the landing gear. To retract the landing gear, the pilot moves the valve lever in the opposite direction, allowing oil to flow into the other end of the cylinder. 2. Multiplication of force. A fluid power system (without using cumbersome gears, pulleys, and levers) can multiply forces simply and efficiently from a fraction of an ounce to several hundred tons of output. 3. Constant force or torque. Only fluid power systems are capable of providing constant force or torque regardless of speed changes. This is accomplished whether the work output moves a few inches per hour, several hundred inches per minute, a few revolutions per hour, or thousands of revolutions per minute. 4. Simplicity, safety, economy. In general, fluid power systems use fewer moving parts than comparable mechanical or electrical systems. Thus, they are simpler to maintain and operate. This, in turn, maximizes safety, compactness, and reliability. For example, a new power steering control designed has made all other kinds of power systems obsolete on many off-highway vehicles. The steering unit consists of a manually operated directional control valve and meter in a single body. Because the steering unit is fully fluid-linked, mechanical linkages, universal joints, bearings, reduction gears, etc. are eliminated. This provides a simple, compact system. In applications. This is important where limitations of control space require a small steering wheel and it becomes necessary to reduce operator fatigue. Additional benefits of fluid power systems include instantly reversible motion, automatic protection against overloads, and infinitely variable speed control. Fluid power systems also have the highest horsepower per weight ratio of any known power source. In spite of all these highly desirable features of fluid power, it is not a panacea for all power transmission problems. Hydraulic systems also have some drawbacks. Hydraulic oils are messy, and leakage is impossible to completely eliminate. Also, most hydraulic oils can cause fires if an oil leak occurs in an area of hot equipment. Pneumatic System Pneumatic system use pressurized gases to transmit and control power. As the name implies, pneumatic systems typically use air (rather than some other gas ) as the fluid medium because air is a safe, low-cost, and readily available fluid. It is particularly safe in environments where an electrical spark could ignite leaks from system components. In pneumatic systems, compressors are used to compress and supply the necessary quantities of air. Compressors are typically of the piston, vane or screw type. Basically a compressor increases the pressure of a gas by reducing its volume as described by the perfect gas laws. Pneumatic systems normally use a large centralized air compressor which is considered to be an infinite air source similar to an electrical system where you merely plug into an electrical outlet for electricity. In this way, pressurized air can be piped from one source to various locations throughout an entire industrial plant. The compressed air is piped to each circuit through an air filter to remove contaminants which might harm the closely fitting parts of pneumatic components such as valve and cylinders. The air then flows through a pressure regulator which reduces the pressure to the desired level for the particular circuit application. Because air is not a good lubricant (contains about 20% oxygen), pneumatics systems required a lubricator to inject a very fine mist of oil into the air