Vibration steady-state response analysis and vibration reduction design of reciprocating cutter

The cutter is an important part of the harvester, and the commonly used cutter has

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.

excitation

response

enter

Output

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

And X2

(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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