The tightening of bolts for assembly in the machine industry is a common phenomenon. Previously, people only considered screwing bolts (or nuts) to the tightest extent during assembly. Later, people discovered that this "tightest" is just a very vague concept, which varies from person to person. There are dozens of machines, and hundreds of parts are bolted and assembled. In large production, it is done by most people at different times. And to assemble dozens or hundreds of machines every day, this "tightest" dispersion will be imaginable. In addition, some parts (such as the big hole in the connecting rod of the automobile engine) need to be assembled by bolts in the production workshop. When the assembly shop is assembled, the bolts must be loosened and the tile cover removed. After tightening on the crankshaft and then retightening it, it is conceivable that the result will be very dangerous. Therefore, how to effectively control the "tightening" and make it "best" has become a topic of great concern to the machinery industry. In this way, not only the discussion and application of the tightening control method has become a hot topic, but also the application of the automatic tightening machine has become increasingly widespread.
One. Common tightening methods and applications of the tightening machine
For the control method of bolt tightening, we introduced five kinds in the last section, but there are only two kinds of applications in the current mechanical processing industry. They are the torque control method and the torque-angle control method. Among them, the torque control method is usually applied to the case where the tightening requirement is not too high, and the fixed value torque wrench or the automatic tightening machine can be used. Since the fixed torque wrench structure and its use are relatively simple, it is not allowed here. Introduction. The torque-rotation control method basically uses an automatic tightening machine. Before introducing the automatic tightening machine, it is necessary to give a brief description of the classification of the tightening machine. There are several ways to classify the automatic tightening machine. If it is divided according to the tightening control method, it can be divided into the torque control method, the tightening-angle control method and the yield point control method. If it is divided according to the degree of human participation, it can be divided into Manual and automatic tightening machine; if the energy properties of the components are tightened, they can be divided into pneumatic and electric tightening machines. Among them, the electric tightening machine can be divided into a DC tightening machine and an AC tightening machine according to the nature of the power supply of the components, and the execution components thereof are a DC servo motor and an AC servo motor. Below we only introduce the structure and control detection principle of the automatic tightening machine of these two kinds of tightening methods.
two. The structure and principle of the torque control method tightening machine
Because the tightening control of the torque control method is simple and inexpensive, it has been widely used in some cases where the tightening requirements are not high, such as oil low shell, upper cover, crankshaft oil seal, flywheel in engine assembly. , Camshaft cover, camshaft sprocket, tightening of bolts such as cam bush cover in engine parts machining. In practical applications, most of the tightening machines for torque control are now electric type, but some manufacturers of pneumatic type are still in use. The principle and method of torque detection are basically the same, and the difference is that they are used. The energy is corresponding to the tightening of the components, so the method of control is quite different, but the principle of tightening is the same. Since the current application of our factory is electric tightening machine, we only use the electric tightening machine. Introduction.
1. Torque control method
The block diagram of the torque control method is shown in the figure. It can be seen from the figure that it consists of 9 links: power conversion, motor driver, servo motor, reducer, torque sensor, output shaft, master Unit, axis control unit and display. Its energy source is AC power.
The actuator for the electric tightener is the servo motor, and the one that drives the servo motor is the motor driver. Among them, the servo motor has the distinction of AC and DC. Among them, the drive of the AC servo motor, the nature of the power supply is AC, so the function of the power conversion part is only to convert the AC input from the AC power into a suitable motor driver and The voltage value required for the servo motor to work normally (ie, the transformer) can be used. For the driver of the DC servo motor, since the nature of the power supply is direct current, the power conversion part must have a voltage value such as an AC system. In addition to the change, the AC power after the transformation is rectified and converted into DC power. However, whether it is a DC servo motor or an AC servo motor, its structure is now in the form of a brushless (ie, no brush).
2. Torque control method The working principle of the tightening machine is as follows:
When the control system of the machine tool issues a tightening running command, it directly enters the main control unit to generate a reset and start control signal, which directly enters the axis control unit, on the one hand resets it (reset to restore the original state), and On the one hand, the motor driver is given an operation command to operate it, and the input AC power source is converted according to different requirements (DC or AC), output, and sent to the servo motor for rotation. The rotational torque of the servo motor is output from the output shaft, that is, the workpiece is tightened, and the torque during the tightening process is extracted by a torque sensor connected in series between the servo motor and the output shaft, and sent to the axis control unit. During the tightening process, as the tightening progresses, the torque continuously increases. When it reaches the set torque value, the axis control unit immediately sends a control signal to the motor driver, and under the control of the drive, the servo motor stops immediately. Rotate to complete the tightening work. After the tightening is completed, the axis control unit sends out two signals for the result of tightening. One of them is to send out the display signal, and the display signal is divided into two parts, one is the actual torque peak of tightening, and the other is the tightening result. Actual state (including the torque value is acceptable, the torque is higher than the upper limit value and the torque is lower than the lower limit value); on the other hand, the actual state of the tightening result (mainly the torque value is qualified or unqualified) is converted by the main control unit. After that, it is sent to the control system of the machine tool, so that the control system of the machine tool can judge and select the next tightening work.
three. Torque-angle control method and its principle
Because the torque-rotation control method of the tightening machine is more complicated and the price is relatively higher, it is usually applied to the occasions with high requirements for tightening, such as the cylinder head, the pulley, the crankshaft main bearing cover and the engine assembly. Connecting rod cover, tightening of bolts such as crankshaft main bearing cover and connecting rod cover in machining engine parts. In practical applications, the torque-angle control tightening machine is now basically of the electric type, and the pneumatic type is rarely used, and the principles and methods of torque and angle detection are basically the same. As with the torque control method, the difference is only the energy used and the corresponding tightening of the components, so the method of control is equally large. Below we will take the electric tightening machine as an example.
1. Torque-angle control method
The block diagram of the electric torque-angle control method is shown in the figure. It can be seen from the figure that it consists of 10 links: power conversion, motor drive, servo motor, angle sensor, reducer, torque sensor. , output shaft, main control unit, axis control unit and display. Its energy source is AC power.
In practical applications, the torque-angle control tightening machine is now basically of the electric type, and the pneumatic type is rarely used, and the principles and methods of torque and angle detection are basically the same. As with the torque control method, the difference is only the energy used and the corresponding tightening of the components, so the method of control is equally large. Below we will take the electric tightening machine as an example.
2. Torque-angle control method The working principle of the tightening machine is as follows:
When the control system of the machine tool issues a tightening running command, it directly enters the main control unit to generate a reset and start control signal, which directly enters the axis control unit, on the one hand resets it, and on the other hand, the motor driver is operated. The command is run to operate, and the input AC power source is converted according to different requirements and output, and sent to the servo motor to be rotated. The rotational torque of the servo motor is output from the output shaft, that is, the workpiece is tightened. The torque during the tightening process is extracted by a torque sensor connected in series between the servo motor and the output shaft, and sent to the axis control unit. The corner during the tightening process is thrown out by the angle sensor and sent to the motor driver, which is converted into the axis control unit. Since the torque-rotation control method is tightened by first screwing the bolt to a set torque value, and then starting from this point, screw a set angle control method. Therefore, the tightening process of this method is: during the tightening process, as the tightening progresses, the torque value continuously increases, and when it reaches the set conversion torque value, the corner counter is immediately inside the axis control unit. Clear “0â€, and then start counting the corner. When the count value reaches the set corner value, the axis control unit immediately sends a control signal to the motor driver, and under the control of the driver, the servo motor stops rotating immediately. This tightening work. In order to prevent accidents, such as the occurrence of small screw holes, blockages or insufficient thread depth of the workpiece, when the tightened torque reaches the set torque value, if it is to be screwed to the set rotation angle, it is highly probable that The bolts are broken and cause undue losses. Thus, for the tightening method of the torque-rotation control method, a limit value of the maximum torque is set for the protection against such an accident. That is, there are two conditions for controlling the servo motor to stop rotating, one of which is mentioned above - the set angle is reached; the other is that the set maximum torque value is reached or exceeded, that is, although the set corner value is not reached, When the set maximum torque value is reached, the servo motor is also required to stop running. The control signal is also sent from the axis control unit, that is, the axis control unit controls the servo motor to stop running. There are two conditions, one is to reach the set rotation angle, and the other is to reach the set maximum torque. Among these two conditions, Just meet one. After the tightening is completed, the axis control unit sends out two signals for the result of the tightening. One of them is to send out the display signal, and the display signal is divided into three parts, one is the actual torque peak of tightening, and the other is the actual tightening. The corner value, the third is the actual state of the tightening result (including the pass, the torque is higher than the upper limit and the torque is lower than the lower limit, the corner is higher than the upper limit and the angle is lower than the lower limit); on the other hand, The actual state of the tightening result (mainly the qualified or unsatisfactory tightening value) is converted into the control system of the machine tool after being converted by the main control unit, so that the control system of the machine tool can judge and select the next tightening work.
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