Physical and mechanical calculation of the efficiency of a composite kick shock absorber and the friction force with the material

The article presents an effective structural scheme with a rubber shock absorber for the sewing machine. As a result of the theoretical research, analytical methods were used to calculate the coefficient of uniformity of the rubber shock absorber with a component bearing and to determine the friction force between the bearing and the material being sewn. Parameter connection graphs were determined. Based on the results of the analysis, the parameters of the proposed compositional reaction node were developed.


Introduction
During the sewing process, there must be enough friction between the needle and the material to ensure that the material is pushed evenly along the length of the seam.In this process, due to a number of reasons, the frictional force decreases cyclically due to the vertical vibration of the wheel.This does not ensure that the bahias are formed evenly.The vertical vibrations of the shaft are partially reduced when cylindrical and conical [1] springs used in existing machines [2,3] are used.In this case, the use of a rubber shock absorber in the proposed construction of the wheel [4] significantly reduces the vertical vibrations of the wheel.Because rubber shock absorbers have higher damping properties compared to springs [5].It is important to determine the friction force between the surface of the lower part of the tire and the material being sewn when using the recommended tire construction.The amount of pressure required to press the foot on the material being sewn depends on the thickness of the material.The determined tension N corresponds to the maximum thickness of materials that can be sewn on the machine in question.In other cases, this value will be smaller.The thickness of the material to be sewn on heavy duty machines can be taken much thicker than on universal machines, which is equal to N.
During the operation of the sewing machine, the rod attached to it vibrates vertically along with the stem.The reason for this is that the rod 1 and rod 3 (figure 1) are compressed by the spring 12, representing an elastic system that is in the mode of forced vibrations during operation of the machine.The source of forced vibrations is the push gear rack, which during operation of the machine raises the shaft relative to the needle plate, and then lowers it again.In sewing machines, sufficient frictional force must be created between the conveyor rail and the materials to move the materials being sewn.This force is provided by tire pressure.Another main function of the kicker is to keep the material being sewn at the level of the needle plate when the needle and thread puller are raised.In addition, it is necessary to ensure a certain amount of compression of the materials being sewn.This greatly facilitates adequate tensioning of the seams with the thread tensioner and ensures the appearance of elastic forces that create sufficient tension in the seams even after the reaction stops on the material.In the construction of the 22-A-class sewing machine known to us, the wheel is fixed to the moving vertical rod with a screw.The kick consists of a base and a hinged holder.The kick star can move parallel to the needle holder on the guides mounted on the machine head.A bracket with a push-out guide, which moves when the wheel is raised, is mounted on the steering wheel in the long slot of the machine head.This prevents the stern from rotating on its own axis.When raising the kicker by hand, it is necessary to screw a special ball through the offshoot.In the 22-A-class sewing machine, the reaction pressure on the materials being sewn is created by a cylindrical spring that is attached to the steering wheel.Some sewing machines, for example, class 97 machines, use flat springs instead of cylindrical springs.Such a spring has no special advantages over a cylindrical one.
In sewing machines, in order for the transport rail to move the materials being sewn, sufficient friction force must be created between it and the materials.This force is provided by the pressure of the presser foot.The purpose of the presser foot is also to hold the stitched materials level with the needle plate as the needle and thread take-up move upward.In addition, the presser foot must provide a certain compression to the materials being sewn.This greatly facilitates the tightening of stitches with a thread take-up and ensures the appearance of such elastic forces in compressed materials that create sufficient tension in the stitches after the influence of the presser foot on the materials ceases.

Determining the stiffness of the rubber shock absorber
The design of the shock absorber directly affects the friction force.Therefore, it is necessary to determine the integrity of the rubber shock absorber figure 1 shows the scheme of the proposed structure in working condition.It is known [5,6] that the total weight forces of the steering wheel, spring, upper and lower parts of the wheel, and the rubber shock absorber are mutually balanced according to the static condition [7], and the restoring force of the spring, rubber shock absorber, and the deformation of the materials are in mutual balance [8].
It should be noted that the deformation of the sewn materials depends on their uniformity coefficients.Therefore, they are generally given coefficient of singleness [11], in two-layer materials: in three-layer materials Putting the received (2), ( 3) into (1), taking into account the parameter expressions, we create the formula for determining the uniformity of the rubber shock absorber with a component: Numerical results of the problem were obtained in the case of graphs of the dependence of the values of the parameters on the consistency of the rubber shock absorber.Figure 2 shows the graphs of the dependence of the coefficient of uniformity of the rubber shock absorber with a composite bearing unit on the ratio of the coefficients of uniformity of the spring and the materials being sewn, and the total mass value.From the analysis of the graphs, it should be noted that when the total mass is 5.0•10-1 kg, and when the mutual ratio of the total uniformity coefficients of the push spring and sewn materials is increased from 0.5 to 1.5, the uniformity coefficient of the rubber shock absorber is 1.8•103 N/m.It decreases from m to 0.76•103 .The main reason for this is that the higher the stiffness of the compression spring and the softer the material, the lower the coefficient of elasticity of the rubber.Accordingly, with the increase in the total mass of the suspension mechanism, it is necessary to increase the stiffness of the shock absorber.In particular, when the value of m y increased to 8.6•10-1 kg , it was found that the coefficient of uniformity of the rubber shock absorber decreased linearly from 2.0•103 N/m to 1.5•103 N/m (figure 2).In particular, when the value of m y increased to 8.6•10-1 kg, it was found that the coefficient of uniformity of the rubber shock absorber decreased linearly from 2.0•103 N/m to 1.5•103 N/m (figure 2).It should be noted that high deformation values of the rubber shock absorber increase the amplitude of the vibration of the pressure force of the material, the friction changes, and the quality of the resulting bag decreases.Therefore, in order to ensure that the values of ∆y r do not exceed 1.0•10-3 m, csc=(1.8÷2.0)•103N/m, cmc=(2.2÷2.6).It is recommended to be in the range of 103 N/m, mym=(7.5÷8.0)•101kg.

Determining the friction force between the lower part of the composite wheel and the material
It is known that the force of friction between the reaction and the material to be sewn mainly depends on the pressure force of the materials.So, when calculating the pressure force, the steering mechanism of the suspension mechanism, the compression spring, the weights of the composite suspension and the unit forces of the spring and rubber shock absorber are affected [12], that is: Fb = mst g + msc g + (mtd + mtp )g + mr g -cpr ∆ysc -cr ∆yr (5) Accordingly, the frictional force between the reaction and the material [13]: (6) obtained on the basis of the values of the above-mentioned parameters was carried out.But if the friction force is too great, the material will be crushed, the load on the rail will increase, and the material will be crushed.Therefore, the recommended values are: csc = (1.2÷2.0)•103N/m, cpc = (2.2÷2.5)•103N/m. Figure 4 shows the graphs of the friction coefficient between the reaction and the material being sewn, depending on the friction force.In general, the coefficient of friction between the needle and the materials to be sewn mainly depends on the characteristics of the materials being sewn, the smoothness of the surface of the needle.Therefore, if the coefficient of friction is not high, it is necessary to increase the pressure force of the bearing.Because if the friction is not enough, the material will not be pushed uniformly.Based on the analysis of the obtained graphs, it can be noted that when the coefficient of friction between the reaction and the material being sewn is increased from 0.05 to 0.3 and the value of the total mass of the system is 3.5•10 -1 kg, the friction force between the reaction and the material F heat values 0.38 N to 2.08 N increases in a linear fashion.Correspondingly, when the coefficient of friction between the reaction and the material f increases mym = 7.2•10-1 kg, the values of the friction force increase and increase from 0.74 N to 4.53 N in linear connection.As mentioned above, the following values of the parameters are recommended to ensure sufficient friction force between the surface of the bottom part of the tire and the material being sewn: mym = (6.5÷7.0)•10-1kg, f = (0.1÷0.16).

Conclusion
A structural scheme with a rubber shock-absorbing bearing, which provides quality stitches when sewing materials on a sewing machine, is recommended.On the basis of theoretical studies, formulas were obtained for calculating the strength of the rubber shock absorber with a composite wheel and the friction force between the wheel and the material.The parameters of the reaction node are based on the analysis.

Figure 1 .
Figure 1.Scheme of the proposed reaction structure in working condition.

Figure 2 . 4 .
Figure 2. Graphs of the dependence of the coefficient of uniformity of the rubber shock absorber with a composite rod on the ratio of the coefficients of uniformity of the spring and the materials being sewn, the total mass value 1 -mym = 8.6•10 -1 kg; 2 -mym = 6.8•10 -1 kg; 3mym = 5.0•10 -1 kg;