Working principle of table tennis server
Table tennis server is a comprehensive technical product integrating electronics, machinery and computer technology. It has the characteristics of high automation, high sensitivity, stability and reliability. Its basic working principle is the principle of using the wheel to rub the ball. Table tennis can get a certain initial speed because of the action of a rotating friction wheel, which works under the control of DC motor. When the motor drives the driving wheel to rotate, it will rub the table tennis, so that the ball can gain some kinetic energy, and then the table tennis can be launched. This principle scheme is simple and practical, which can not only ensure the stability of table tennis launch, but also control the angle and speed of table tennis launch well, so that users can practice playing table tennis at will.
Let the angular velocity of the wheel be ω and the radius be r, then the linear velocity of the wheel can be calculated: v = ω× r.
Then the speed of tennis in an instant is V, which is the initial speed of table tennis.
Therefore, the initial speed of table tennis can be obtained by measuring the linear speed of the wheel.
2 Table Tennis Server Workflow
The working process of the table tennis server is to first store the table tennis in the ball storage box. The power supply is turned on, and the motor in the ball device works, and the agitator in the ball storage device is driven to rotate through the gear transmission mechanism, and the table tennis ball enters the ball delivery device through the funnel. The ball is delivered by the rotation of the impeller in the ball delivery device and reaches the ball outlet of the machine head through the ball delivery pipeline. The impeller is also driven by the motor through the transmission mechanism, and the rotating speed of the impeller is controlled by the PWM pulse width modulation of the DC motor, so that the number of balls sent out in a unit time can be controlled. After the table tennis ball reaches the ball outlet, the driving wheel rotates and rubs the table tennis ball, thus sending the ball out. Press the button on the box of the left-right swing device of the nose, and realize the left-right swing of the nose through the crank-rocker mechanism in the box. The manual mediation button on the mediation head can adjust the head up and down through the spring device on the head. 3 overall structure design of table tennis server
The overall structural design of the table tennis server includes the design of the base part, the design of the ball delivery device, the design of the fairway, the design of the ball storage device, the design of the adjusting device, the design of the head part and the selection of the motor.
3. 1 Determination of overall scheme of table tennis server
3. 1. 1 Table tennis server design requirements:
The main requirements that the table tennis server needs to meet are as follows:
1, let users have a better grasp, more points and more angles.
2. Ball frequency: 30-72 times/minute; Feed speed: 4-50m/s
3, hitting angle: 30 degrees adjustable range; Curvature of the ball: 40-degree adjustable range
4. Ball speed and ball frequency are operated by remote control.
3.2.2 Determination of the overall plan:
According to the above requirements, the overall scheme of this service machine is determined as follows:
1, the body material is mainly reinforced plastic and ABS. Some parts are made of high-quality steel, and the advantages of these materials will be introduced in detail below.
2. Serve by using the principle that the friction wheel fixed at the ball outlet rotates to friction table tennis. The ball outlet is driven by a single wheel, which can adjust eight directions, so that the sent table tennis can rotate in eight different ways.
3. The ball feeding device, ball mouth driving wheel device and agitator in the ball storage device are all driven by low-power DC motor.
4. The nose swings back and forth left and right through the crank-connecting rod device, and the crank-wheel device is still driven by the DC motor.
3.2 Design of Basic Part
The bottom of the server adopts four roller devices. On the one hand, the four rollers can bear the weight of the machine body, on the other hand, the machine body can be easily moved by using the rollers, which brings convenience to users. The bottom plate is made of thin metal parts, which can bear the weight of the machine body well.
3.3 Design of ball delivery device
The ball feeding device is the core part of the whole table tennis server, and it is also an important standard to measure whether a table tennis server has superior performance. Therefore, whether the ball delivery device can successfully realize the expected ball delivery function is related to the successful design of the whole set of products. Therefore, the design of ball delivery device is an important link in the whole product design.
The device adopts an impeller rotating ball feeding mechanism, and the impeller is driven by a DC motor to drive the gear transmission mechanism. The impeller can send six balls in one rotation. The PWM pulse width modulation of DC motor can change the motor speed, thus changing the impeller speed, thus changing the ball delivery frequency. The middle partition where the impeller is located and the mail glass plate form a closed space. In order to prevent the ball from sticking, there is a curved fairway behind the impeller, so that table tennis can smoothly enter the ball delivery pipeline. Two DC motors are designed in the ball delivery device. One motor drives the impeller and agitator to rotate through gear transmission at the same time, and the other DC motor drives the crank-link mechanism to realize the left-right swing of the nose. The selection of motor will be introduced in the next chapter.
3.4. Selection of materials
In the ball conveying device, the shell, impeller and middle partition are made of reinforced plastic, which has the characteristics of high strength, high stiffness and good toughness. It has good wear resistance, fatigue resistance and high thermal deformation temperature. From the characteristics of reinforced plastics, it is suitable for these parts.
In the ball feeding device, three pairs of transmission gears and gear shafts are all made of ABS material by injection molding. The characteristics of ABS material are: ABS is a ternary polymer based on styrene-butadiene-acrylonitrile, so it has good comprehensive properties, that is, high impact toughness and good mechanical strength; Excellent heat resistance, oil resistance and chemical stability; Stable size, easy molding and processing, and the surface can cross with metal; Good electrical performance. In view of the above excellent characteristics of ABS material, it is suitable for gears with high speed, high strength, high impact toughness, high local temperature and complicated machining, so ABS is specially selected as the manufacturing material of three pairs of gears and gear shafts.
3.4. 1 impeller design
The function of the impeller is to send the ball into the ball delivery pipeline smoothly through its rotation. The impeller of this set of service machine adopts six-blade mechanism, that is, six balls are transported in one turn, which is made of ABS material by injection molding. The blade thickness is 42 mm.
3.4.2 Design of intermediate partition
The role of the middle partition is to place the blades, motors and bearings, and surround the motors, blades and table tennis with plexiglass. Therefore, the thickness of the partition wall should comprehensively consider the above factors. See the component drawing of CAD ball delivery device for the specific dimensions of the intermediate partition.
3.5. Design of transmission gear
In this design, three pairs of gears, two pairs of helical cylindrical gears and a pair of bevel gears are used for transmission. That is, the rotation of the impeller and the agitator can be controlled at the same time. Because the transmission torque of gears in this set of equipment is relatively small, and the strength requirements of gear materials are not very high, ABS is chosen as plastic gears and manufacturing materials.
Plastic gears are favored by many transmission mechanisms and R&D engineers because of their light weight, wear resistance, corrosion resistance, small vibration, low noise, stable chemical properties, low processing cost and convenience for mass production. The design process is generally divided into the following parts: gear pair theoretical design, gear mold design, gear mold manufacturing, and gear injection production. The process is shown in the following page:
In view of the fact that the most commonly used plastic gear is involute gear with small modulus, the spur gear modulus of this system is selected as 1. Now choose a pair of spur gears to design their parameters:
1, modulus: m= 1
2. Tooth number: Z 1=60mm, Z2= 120mm, that is, the transmission ratio i=2.
3. The diameter of the cyclotron: d 1=60mm, d2= 120mm, so the center distance is a=90mm.
4. Pressure angle: α =
5. Tooth crest height coefficient: = 1, so the tooth crest circle diameters of the two gears are: =62mm, = 122mm.
6. The backlash coefficient is =0.2, so the diameter of the root circle of the two gears is =57.6mm, =117.6 mm..
The parameter selection method of other gears is the same as this pair of gears, so I won't introduce them one by one.
3.6 Design of transmission shaft
The transmission shaft is made of reinforced solid plastic by injection molding. The design of transmission shaft refers to the design method of metal shaft, and the first pair of transmission shafts is selected for design:
The first pair of shafts are connected with a motor and a gear. It is known that the speed range of the motor after pulse width modulation is 10r/min-24r/min, and the motor power is 50W.
That is, the minimum diameter of the shaft d = A0mm = 100× 17mm.
That is, the minimum diameter of the required shaft is 17mm, and the diameter of the shaft designed by this system is 20mm, which can meet the requirements.
3.7 Design of ball delivery pipeline
The basic design principle of the service fairway is that table tennis can be delivered to the service port smoothly, and the ball cannot get stuck in the middle.
The water supply pipe is made of reinforced plastic, which can reduce the weight borne by the base and facilitate installation and fixation. On the other hand, the manufacturing cost can be reduced. The lower part of the ball delivery pipeline is connected with the boss of the top cover of the ball delivery device through four screws, and the upper part is in interference connection with the adjusting spring of the machine head, so as to ensure that the table tennis can smoothly enter the service port of the machine head. The middle part of the fairway is also provided with a collar connected with the recycling net.
3.8 Design of ball storage device
The ball storage device is a table tennis clamping device, which is responsible for sending table tennis into the ball delivery device smoothly.
In design, the material of the ball container is reinforced plastic, and the lower end of the ball container is designed as an inclined plane, so that table tennis can be concentrated at the mouth of the ball container. In order to further prevent the ball from being stuck in the fairway due to the pressure generated by the mutual extrusion of table tennis, a stirring device is arranged at the bottom plate of the ball storage device near the ball opening. The continuous static pressure between balls is eliminated by the stirring of the stirrer, thus effectively preventing the ball from sticking.
3.9 the design of the nose
The nose is the device that finally realizes the service, and it is the device that realizes the function in the whole system. So this device is also an important part of the whole table tennis server. The design of the machine head in this system mainly includes the following parts: service port, service motor, turntable and spring.
The ball outlet is 40mm in diameter and 5mm in thickness. This material is reinforced plastic. The machine head can automatically swing left and right through the lateral swing device and move up and down through the manual button and spring device.
3. Design of10 regulating device
The adjusting device is a typical design part of table tennis serving machine to realize intelligence and humanization. The function of this part is to drive the nose to swing left and right, so as to send table tennis from all directions. Greatly simulated the artificial sparring.
According to the characteristics of the nose, the crank-rocker mechanism is selected to realize the left-right swing of the nose. The DC motor in the ball feeding device drives the crank rod to rotate, and then the turntable moves left and right through the traction of the rocker, so that the nose fixed on the turntable swings left and right. By properly designing the length of the crank rod, the length of the rocker and the distance between the center of the turntable and the fixed position of the crank rod, the corresponding angle range of the handpiece can be set.
In this design, the length of crank rod is selected, the length of rocker is 120mm, the distance between the center of turntable and the fixed position of crank rod is selected, and the nose is in the right center position, so that when the rocker reaches the limit position, the nose can swing symmetrically from left to right with an included angle of 30 degrees.
3. 1 1 Summary
In this chapter, the design principle and overall structure of table tennis serve machine are generally explained, and the functions of its corresponding parts are also introduced in detail, and specific design schemes are put forward for the practical problems of the machine. This will be of great benefit to the manufacture of table tennis server and the development of this work.
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