The hottest steel ball force increasing hydraulic

Steel ball force increasing hydraulic fixture

in the fixture design, the combination of appropriate mechanical force increasing mechanism and hydraulic transmission technology can effectively reduce the working pressure of the hydraulic system and prolong its service life. However, when the common lever force increasing mechanism, hinge force increasing mechanism and wedge force increasing mechanism are used in hydraulic fixtures, the fixture structure is often not compact, or Nanjing University of technology has been working on it since 2000 γ- PGA and ε- The friction loss of PL's basic and industrialization research is large. The steel ball force increasing hydraulic fixture we studied basically overcomes the above shortcomings

1 double steel ball force increasing mechanism and rodless hydraulic cylinder

1) working principle

Figure 1 shows the hydraulic fixture composed of double steel ball force increasing mechanism and rodless hydraulic cylinder. Its working principle is: when the reversing valve is in the position shown in the figure, the pressure oil flows to the left chamber of the hydraulic cylinder, the piston moves to the right, and the steel ball placed in the middle hole of the piston pushes the steel ball at the upper right upward; The steel ball on the upper right pushes the clamping element on the fixture with the output force F to clamp the workpiece before entering and leaving the factory. When the reversing valve is switched to the right position, the piston moves to the left to loosen the workpiece

1. Steel ball 2 Hydraulic cylinder block 3 Force action line 4 Piston

Figure 1

2) mechanical calculation

after establishing a mechanical model and analyzing it, it can be seen that if the friction loss in the process of force transmission is ignored, the calculation formula of the theoretical output force ft (unit n) and the theoretical force increasing coefficient it of the system shown in Figure 1 is

where D - piston diameter, m

p - hydraulic cylinder.Left chamber pressure, pa

α T -- theoretical pressure angle, RAD or (°)

the actual output force FP (unit n) and the actual force increasing coefficient IP of the system shown in Figure 1 can be obtained from the following approximate calculation formula

tanat+tanj (3) IP ≈

fp=1 (pd2p/4) tanat+tanj (4)

, where φ Is the friction angle between the piston and the inner wall of the hydraulic cylinder, in rad or (°), i.e φ= Arctan (friction coefficient between piston and inner wall of hydraulic cylinder)

it should be noted that equations (3) and (4) are obtained under the condition of ignoring the friction loss between steel balls and between steel balls and their constraint holes. In addition, when designing the fixture structure, it should be noted that the piston should be equipped with a circumferential positioning device

2 three steel ball force increasing mechanism and rodless hydraulic cylinder

Figure 2 shows the hydraulic fixture composed of three steel ball force increasing mechanism and rodless hydraulic cylinder. Its working principle is: the middle of the piston is milled flat, and a through hole is machined, and a steel ball is built in the hole. When the reversing valve is in the position shown in the figure, the pressure oil flows to the left chamber of the hydraulic cylinder, the piston moves to the right, and the steel ball placed in the middle hole of the piston moves upward in the hole under the action of the steel ball at the lower right, and pushes the steel ball at the upper right upward; The steel ball on the upper right of it pushes the clamping element on the fixture with the output force F to clamp the workpiece

1、5. Steel ball 2 Hydraulic cylinder block 3 Force action line 4 Piston

in the system shown in Figure 2

if the centers of the two steel balls at the upper right and lower right are located on the same vertical line, the calculation formula of the theoretical output force ft and the theoretical force increase coefficient it is

ft= (pd2p/4)/2tanat (5)

it=ft/(pd2p/4) =1/2tanat (6)

for the system shown in Figure 2, the actual output force FP and the actual force increase are small due to the friction loss in the process of force transmission.Coefficient IP, It can be replaced by theoretical formula for approximate calculation

3 technical performance comparison

the technical performance comparison of the two systems shown in Figure 1 and Figure 2 is as follows:

1) in terms of structural compactness and structural rigidity, the system in Figure 1 is superior to the system in Figure 2

2) when the effective displacement of the piston is the same, the output displacement of the steel ball in the upper right corner of the system in Figure 2 is twice that of the system in Figure 1

3) the system in Figure 2 is superior to the system in Figure 1 in terms of piston stress conditions. It is not difficult to see that the piston in the system in Figure 1 bears a large radial force, while the piston in the system in Figure 2 bears a negligible radial force

4) determined by the force conditions of the piston, the friction loss of the system shown in Figure 1 is significantly greater than that of the system shown in Figure 2. Although from the comparison of calculation formulas (2) and (6), the value of the theoretical force increasing coefficient it of the system shown in Figure 1 is twice that of the system shown in Figure 2. However, due to the large friction loss of the system shown in Figure 1, when the theoretical pressure angle is small, the difference between the actual force increasing coefficient IP of the two systems is not significant. For example, set α t=8°， φ= 6 °, the actual reinforcement coefficient of the system shown in Figure 1 and Figure 2 is IP1 ≈ 4.01 and IP2 ≈ 3.56 from formula (4) and formula (6). The actual reinforcement coefficient of the system shown in Figure 1 is only 3 times the 1.1 overweight lithium battery investment of many listed companies such as BYD, Shanshan, dadongnan, camel, etc. of the system shown in Figure 2

4 conclusion

1) the fixture system composed of steel ball force increasing mechanism and rodless hydraulic cylinder has the advantages of simple and compact structure and simple manufacturing process; The disadvantage is that the contact between the steel ball and its components is point contact, and it is not suitable to bear excessive load

2) the comprehensive technical performance index of the system composed of three steel ball force increasing mechanism and rodless hydraulic cylinder is better than that of the system composed of two steel ball force increasing mechanism and rodless hydraulic cylinder, which should be preferred when designing fixtures

3) steel ball force increasing hydraulic fixture is suitable for small and medium-sized machine tools requiring clamping automation. (end)