## 15 Jan Principle of the motor（2）

**Resonance concept**

Like swinging

1.A push is hard to swing high.

2.The best way is to push in the same direction as the swing moves;That’s the frequency of the push and the swingThe same frequency.A swing has its own natural frequency, and resonance occurs when the driving force is in line with the natural frequency.To correspond to a linear motor is to require that the frequency of the driving force be consistent with the natural frequency of the motor.Since the usage frequency is regulated by the mobile phone, f0 consistency is required in manufacturing.In general, the amplitude achieved by resonance is Q times the magnitude of the primary thrust, Q=27.3*f0/D, approximately 30.**vibration quantity**

Vibration formula：a=mx(2pif)^2/M

1.m:The mass of the weight, which is mainly a design consideration, has a very small dispersion in production.

2.f:Operating frequency: customer requirements.

3.M:Test fixture mass: customer requirements.

4.x:Vibration amplitude of weight, which is the most easily fluctuated in production.

There are two necessary conditions for reaching the required swing range:

4.1A resonance swing has to reach a certain amplitude, just like a swing.

4.1.1The swing is proportional to the driving force.

4.1.2The swing is inversely proportional to the damping.

4.1.3The key is the effect of resonance, swing amplitude and f0 are greatly affected (see sweep curve).

4.2Vibration space: if the space is not enough, swing is limited, also can not meet the requirements.

The biggest change in production is f0, space, damping.**f0**

F0 formula：f0=(k/m)^0.5/2pi

k is the spring constant, and m is the mass of the weight.

k is affected by multiple responses:

1.Spring design

2.Spring material thickness

3.Spot welding position.

Other factors that affect f0: there are some differences of LRA motor between the actual and the theory, so the driving force, damping, and vibration space have a slight effect on f0. With large driving force, small damping and small vibration space, f0 will rise by 1-2hz slightly.**Vibration space**

1.Maximum space in design: the maximum space reserved in the design, beyond which the oscillator will collide with the stator and make a great noise.It is safe to use 80-90% of the actual space.

2.Physical space:

2.1Spatial symmetry: due to spring deformation, assembly error and other factors will cause the asymmetry of the upper and lower space, the actual available space is determined by the minimum space.

2.2Limit adhesive: the actual available space is equal to the maximum space minus the compressed thickness of the limit adhesive;The total space is generally around 0.6, and the tolerance of limit adhesive +/-0.03 May result in a dispersion of 10%.

When the limit adhesive is thickened, the vibration space decreases and the vibration quantity decreases correspondingly.The limit adhesive becomes thinner, the vibration space increases and the vibration quantity increases, but there will be noise at the same time. The selection of the thickness of the limit adhesive needs to take an optimal advantage between the vibration quantity and the noise.At the same time, the thickness of limit adhesive also has an effect on f0, and the change of f0 will also bring the change of vibration quantity.**The noise**

The noise of the linear motor is caused by the friction or collision between the oscillator and the stator.

A concave block is removed from the corresponding surface of the limit adhesive, and the remaining height after compression is reserved.

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