8 Analysis and calculation of the machine part of the machine The structural calculation of the woodworking machine is basically finished in the previous five explanations. The machine reliability calculation is omitted, because the content is more abstract, and will be supplemented later according to the needs. This time, I will briefly talk about the analysis and calculation of the motion part of woodworking machine tools. Looking at the above, it is equivalent to the motion calculation and dynamic calculation of the gold cutting machine. Of course, compared to the gold cutting machine, what we are talking about should be much simpler.
In the past, woodworking machine tools were driven by concentrated electric power, and the motion was transmitted to the working mechanisms of the machine tool through the intermediate mechanical rigid transmission link. This type of transmission often makes the machine structure very complicated. In order to simplify the machine structure, in recent years, we have adopted the following transmission methods: 1 Replace the single motor drive with multiple motors, so that the complex total motion system of the machine can be decomposed. For a thousand simple and simple component motion systems, 2 develop some special transmission components that combine the electrical, electrical, mechanical and electrical-hydraulic electro-hydraulic fluids with the required rotational speed. Such as DC motor, geared motor, speed-regulating motor and rotor-type hydraulic motor, etc., they can eliminate the intermediate transmission link, directly connect the working mechanism of the machine tool with these components, 3 for reciprocating or stepping motion, has begun Hydraulic, pneumatic and gas-liquid mechanisms are used. It is also possible to connect them directly to the work organization.
The motor reducer, motor transmission and gas-liquid mechanism widely used in modern machine tools have been standardized and standardized, and have been put into mass production. As long as the following principles are followed, the machine tool movement system is simple.
The machine's total kinematic chain is decomposed into a series of individually driven individual component kinematic chains, using standardized and standardized components and transmission components. They can be directly connected to the working mechanism of the machine without an intermediate drive; when direct drive is not possible, the number of transmission links in the intermediate drive chain should be minimized to avoid the use of valuable components such as gears in the intermediate drive.
To use purchased parts, for chain drive, belt drive, flexible coupling, flexible shaft, etc.
8.1 Off-speed transmission Wood cutting machine The main motion of the machine belongs to high-speed motion. The circumferential speed of its working mechanism is calculated in terms of how many times per second. The speed of the main motion axis depends on the diameter of the cutting tool. In recent years, due to the reduction of the tool diameter, the rotational speed (synchronous rotational speed) often exceeds 3000 r/min. It is difficult to achieve using a three-phase asynchronous AC motor of standard frequency. Therefore, each step of directly connecting the working mechanism (P0) and the 供电 frequency power supply (75, 100, 150, 200HE) motor shaft can be stepped, but the difference is after each movement step It is necessary to cut off the drive or to disengage the workpiece from the carrier element. The stepping mechanism designed with double-row chain or belt drive is shown in b, c. Only when the drive is cut off less frequently (generally no more than 10 times per minute) and the workpiece can meet the exact positioning requirements. Adopt these institutions. This action can be achieved with an electromagnetic clutch and a pneumatic stop. The electromagnetic clutch must cut off the drive before the blank approaches the pneumatic stop so that the blank utilizes the inertial override of the mechanism against the pneumatic stop.
8.5 Reciprocating mechanism In the main movement of the row saw and the silver belt, the high-speed reciprocating mechanism is widely used, and in the feeding motion of the station processing machine tool, the low-speed reciprocating mechanism is applied. It is a low-speed mechanism for several typical feed reciprocating motions. It has the following three types of blank fixing or machining actuators: 1 fixed on the slide, 2 in the form of a knife, and 3 in a chain.
Type of reciprocating feed mechanism Woodworking machine tool 2003 a is the simplest rope mechanism for the reciprocating movement of the carriage 1 (with the wood 2 on the carriage). When the speed of the slide is known, the gear ratio of the reducer can be calculated according to the formula of the belt drive (4>. At this time, the friction coefficient of the rope and the drum is K=0.99. In order to make the idle speed of the slide larger than the working stroke, A two-speed geared motor (MBP) can be used with a speed ratio of 1:2 or 1:3. The power of the motor is: the more common mechanism for sliding the carriage is chain (b) or belt (c>, both The mechanism is similar. The carriage 1 is provided with wheels 2 that roll along the guide rails 3, and the carriages are connected to both ends of the chain 4 (or the V-belt 4). The chain or belt is driven by a reduction motor (MP) through a sprocket or a pulley. In order to tension the chain or the belt, the two ends are not rigidly connected with the sliding seat, but are springs that are spring-loaded. i=(2~3)F, F is the traction force.
d and e are the carriage moving mechanisms of the rack and pinion. The rack of d is mounted on a moving carriage. The rack of e is fixed on the machine bed. In order to maintain the rigidity it should have, racks that are not too long (usually less than 2 m) can be mounted on the carriage. Rack and pinion drives are labor intensive to manufacture and are therefore undesirable. By changing the rack and pinion drive to a chain drive, it is easy to manufacture. At this point, the chain can be fixed to the bed to function as a rack, and the gear is replaced by a sprocket.
In some cases, especially when the speed of movement of the carriage needs to be adjusted, hydraulic transmission is often used instead of electric one-to-one mechanical transmission. If the stroke of the carriage is not large (less than 2m), the piston rod or cylinder of the hydraulic actuator can be directly connected to the moving part without the need of the intermediate transmission link (f). If the stroke of the carriage is large, an acceleration device can be used in the middle. . The rack and pinion 1 in g and the chain drive 2 act to accelerate this. At this time, the ratio of the slide stroke to the piston stroke is the sprocket diameter (mm) on the D.?. conveyor.
When the stroke of the slide is A, the stroke of the piston rod is suitable for the slide stroke. The hydraulic plunger mechanism (h) is preferred. Compared to hydraulic cylinders, it has the advantage that the inner surface of the large length plunger does not require precise machining.
In recent years, almost all hydraulic cylinders and cylinders have been used to achieve reciprocating movement of small strokes (stroke less than .5 m). There are many different forms of construction. When designing, standard hydraulic and pneumatic devices should be used as much as possible, and the components should be designed to be compact. i is a knife-type mechanism in which the circular saw blade 1 is reciprocated by means of pneumatic or hydraulic means. In order to make the structure compact, the cylinder 3 is mounted in the guide rail of the tool holder 2 and moved together with the tool holder, and the piston rod 4 is fixed.
In the hinge mechanism of linear silver linear motion, the power cylinder is connected to one of the hinge links (j). In order to achieve the feed movement of a lightweight tool holder, such as a drill press, in recent years an embedded cylinder mechanism with a spindle has been widely used. The main shaft and the piston rod are concentric (k). Here, the piston rod 3 is hollow, and a bearing 1 is mounted therein, and the spindle 2 is mounted on the bearing and connected to the shaft of the motor 5. The cylinder 4 is fixed to the overhanging bracket 7 and is provided with a travel limiter 6, often with a gas distributor.
The piston rod is connected to the flange of the motor and acts as a guide for the moving part of the mechanism.
8.6 Adjusting the moving mechanism On the multi-step woodworking machine, the cutting tool needs to be adjusted frequently in size and position. The requirement to achieve this adjustment mechanism is the accuracy and sensitivity of the movement. At present, the adjustment of the mobile mechanism is manual, mechanized and automated. A typical structure for moving movements.
a is the simplest manual adjustment mechanism that does not meet the multi-process machine design requirements. Such a mechanism is usually a hand wheel 5 through which the platform 2 of the actuator is moved by means of a screw 4 and a nut 3. In order to install accurately, the fixing of the nut utilizes its cylindrical tail. Sometimes, there are some intermediate links between the handwheel and the screw.
The minimum positioning difference of the gapless thread mechanism with intermediate links (regardless of the elastic displacement) is the D handwheel diameter; the ratio of the i?? intermediate motion link.
When considering the clearance (usually in the screw nut pair), 0.2 mm. When designing the adjustment screw mechanism for movement, determine the force on the Fm?? handwheel of the handwheel, fM=30(N), a ?? thread angle, P?? thread friction angle; i intermediate link gear ratio.
b is a rack and pinion moving mechanism. 1 is a gear and 2 is a rack. This mechanism can be used when the amount of movement is large and the accuracy of the mechanism is not high. Under the same conditions as the screw mechanism, the positioning error of such a mechanism is sometimes, and a chain drive can also be used instead of the rack and pinion drive. When the slack of the chain elongation is not considered, the positioning error of the chain drive is the number of teeth of the z-sprocket.
The diameter of the handwheel in the rack and pinion drive is the diameter of the handwheel in the chain drive. | c is a rack and pinion adjustment mechanism with a circular guide. Here the teeth of the rack 2 are milled directly on the circular guide. The gear 3 is driven by a motor of the retarding woodworking machine 2003.
d is a screw mechanism in which the column 1 moves along the bed rail 2 . The lead screw 3 is mounted on the rolling bearing 4 and is connected to the motor 6 via a speed reducer 5. When the length of the screw is greater than 1.5 mm, it is better to fix it on the bed without moving, and let the reduction motor mounted on the moving column to drive the nut to rotate.
The rope mechanism that adjusts the movement is similar to the chain mechanism. However, since the rope is firmly anchored to the drive drum, its accuracy can be higher. Adjusting the mobile program control system is the latest in these types of organizations. e is one of its simplest forms. It is equipped with a counting device for the position of the actuator. The reduction motor 1 drives the screw 2. The saw frame 3 can be moved along the guide rail 4. The lead screw is connected to the digital drum counter 5. Counter 5 can indicate the position of the actuator. When the drum's reading needs to be changed (such as the position of the saw blade change), the handle 6 can be used to change its reading.
More complex program control mechanisms are inseparable from the use of stops or computational techniques.
f is an adjustment device having a rotating drum 4. The drum 4 is provided with a stopper 5. The drum bracket 3 is fixed to the movable blade holder base 2, which is in turn connected to the cylinder housing 1. The piston rod is mounted on a fixed tool holder base plate 7. The bottom plate 7 is also equipped with a block limiter 6. Before the adjustment work, the block is fixed at the desired position, and then the compressed air is fed into the piston chamber. Then the bottom plate 2 pushes the block drum along the A direction. open. After the drum is turned to the desired position, the gas enters the piston rod cavity again, causing the bottom plate 2 to move in the B direction to a new position.
The whole CNC system. The position sensor interacts directly with the floor of the actuator. The motor (M) drives the screw rotation through the speed reducer (P) until the feedback line of the position sensor emits a displacement end signal given by the program device (y). h, i are two similar CNC systems, the difference being that the position sensor (DP) is installed at a different location. The former position sensor is placed on the rotor of the motor (M), while the latter is mounted on the screw.
j is an open loop system (no feedback) driven by a stepper motor (M). After the stepper motor receives each pulse from the program, it turns the screw through a strictly defined angle. Machine tool adjustment for CNC machine tools has not been widely used.
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