There are two basic types of rotary and reciprocating cutters. Among them, reciprocating
The cutter has a simple structure and reliable operation, and can adapt to general or higher operations.
The speed requirement is the most widely used on rice and wheat harvesters.
Cutting performance of reciprocating cutter and physical and mechanical properties of stem
Quality, cutter characteristics, cutting method and cutting speed, etc., cutting speed
The higher the cutting resistance, the better the cutting performance. But with the cutting speed
The degree of increase, the inertial impact and vibration generated by the cutter increase, the cutter is used to
Sexual force cycle changes, causing the cutter to be subjected to non-harmonic excitation
When the excitation frequency is equal to the natural frequency of the system, the machine generates severe vibration, causing component wear and even brittle fracture, thus affecting the machine.
Service life and quality of work. Research on the inertial impact and vibration of the reciprocating cutter, using the superposition principle to the cutter vibration system
Solve the steady state response, understand the critical rate of the cutter, correct
It is important to use cutters and improve the quality of their work.
1 cutter structure
1.1 The composition of the cutter
The cutter is generally made up of a moving blade, a fixed blade, a blade protector, a blade cutter,
The friction plate and the knife bar are composed as shown in Fig. 1. Fixed blade riveting
On the blade, the moving blade is riveted to the arbor, and the blade has a light edge on both sides or
Toothed edge. When cutting, the upper edge of the blade and the fixed blade provide double support.
The knife makes a reciprocating linear motion to shear the crop stems.
Fund Project: 2012 Nantong Science and Technology Innovation Project (HL2010016)
About the author: Yan Shuai (1969-), male, Nantong, Jiangsu, associate professor, master, (E-mail)
5. Moving blade 6. Fixed blade 7. Blade protector
Figure 1 cutter structure
1.2 Transmission mechanism of reciprocating cutter
Reciprocating cutter drive mechanism for changing the rotary motion
Complex linear motion. Commonly used reciprocating cutter transmission mechanisms include a crank linkage mechanism, a swing lever mechanism, and a planetary gear mechanism.
1.2.1 crank connecting rod transmission mechanism
1.2.2 swing ring mechanism
The pendulum ring mechanism is compact in structure and reliable in operation, but the cost is high.
3 is shown.
1.2.3 planetary gear mechanism
The planetary gear mechanism is shown in Figure 4. The length of the crankshaft is equal to
The pitch circle radius of the planetary gear, the pitch circle radius of the planetary gear is the ring gear
2 vibration analysis basis
2.1 Incentive and response
An actual vibration system will be activated by the external excitation F(t)
Presents a certain vibration effect. The excitation is the input of the system, and the response X(t) is the output of the system. The two are connected by the vibration characteristics of the system.
Start. The actual vibration system relationship is shown in Figure 5.
k and ideal damping. It consists of 3 basic components. Figure 6 is common
Single degree of freedom system model 0.
Taking the mass element m as the research object, taking the separation body and drawing the force diagram
As shown in Figure 7. F(t) is the external excitation, Fs(t) is the spring force, and Fd(t) is the damping force.
2.3 Principle of superposition of linear vibration system
(t) separately motivate the response
(t), according to the linear vibration system differential equation
Equation (2) and equation (3) add up
2.2 Vibration system differential equation
2.2.1 Mechanical model of vibration system
Vibration system mechanics model from ideal mass m, ideal spring
According to formula (4), the principle of superposition of linear systems, that is, several incentives
The total response is the sum of the response functions.
3 cutter vibration analysis bookmark6
3.1 cutter mechanical model
The reciprocating straight line of the unbalanced cutter when the crank connecting rod cutter is working
The motion produces an inertial impact that causes the system to vibrate. Multiple cutters
The composition of the part, its simplified mechanical model is shown in Figure 8.
The inertial force of mass Mb is
The total inertial force of the cutter system is
Let the cutter system have a mass of M and a stiffness of K for the cutter system.
The differential equation of motion is
For linear systems, the principle of superposition is used to obtain the system of the cutter
Steady state response is
3.2 cutter steady state response
The mass of the connecting rod is replaced by two masses by mass substitution:
The first mass M1 is located at the crank pin and performs a circular motion with the crank pin;
The second M2 is located at the cutter and reciprocates with the cutter &]. movement
All unbalanced masses can be simplified to two points, A and B, respectively.
Quantitative brother and Zha said that if the cutter quality is Md and the crank pin mass is Mq, then the rotation mass Ma=
The component of the rotational mass inertial force in the horizontal direction is
The mass Mb makes a reciprocating linear motion, and its reciprocating geometric relationship is
12wt(10) according to McLaughlin's expansion r246cosa=1
4 cutter damping design bookmark7
The crank connecting rod cutter generates inertia due to the reciprocating motion of the moving knife
Force and impact load, inertial force is converted to the crank pin, which can be decomposed into
Radial force combined with tangential force. Radial force causes vibration of the frame, affecting the cutter
Life; tangential force causes alternating torque on the crank, affecting cutting
Performance 6_9]. Therefore, the inertia force of the cutter must be balanced,
The system is designed for vibration reduction.
Balance the inertia of the cutter, add weight to the opposite side of the crank
Mp, using the rotational inertia force of Mp to balance. The quality mentioned above
The quantity substitution method solves the inertial force of the connecting rod, and for this reason it is assumed that the connecting rod 1/3 mass
Circumferential movement with the crank pin, 2/3 mass reciprocating with the cutter
Move E0_11. The force applied to the system after adding the weight is shown in Figure 9.
In the crank connecting rod cutter transmission mechanism, the length of the connecting rod is usually
It is several times larger than the radius of the crank, so. According to the steady state response solution, it can be seen that
When the crank rotation rate is equal to the system natural frequency or the crank rotation frequency is 50% of the system natural frequency, the system generates resonance, so it should be avoided.
Free work at these two critical rates.
Proposing a method for balancing the inertial force of a reciprocating cutter
The force balance method reduces the vibration of the cutter and can effectively reduce it.
The vibration of the cutter improves the reliability of the cutter.
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