How to choose a swing cylinder? Analysis on the selection method of swing cylinder

The function of the swing cylinder


The swing cylinder is a pneumatic actuator that uses compressed air to push the swing shaft to swing back and forth within a certain angle range and output torque. Swing cylinders are usually used for indexing, turning over, transporting, pressing, supplying or stopping supply of workpieces, opening and closing valves, bending pipes and driving manipulator rotation, etc.





How to choose a swing cylinder? Analysis on the selection method of swing cylinder


1. Select varieties


A comparison of the characteristics of the two swing cylinders is shown in Table 1. It can be used as a basis for selecting the type of swing cylinder. The comparison items in Table 1 are compared under the condition that the nominal bore diameters of the two varieties of swing cylinders are the same. The values ​​listed in Table 1 are taken from SMC's product samples.
When selecting a variety, the size of the swing angle or the adjustable range of the swing angle must meet the requirements. In some situations, such as when using a swing cylinder on a manipulator, the swing cylinder is also required to be small in size and light in weight.





2. Pre-select the nominal bore size (or model)


2.1 Estimate the moment the swing cylinder will bear based on the nature of the load


Loads can be divided into static loads, resistive loads and inertial loads.​


Static load refers to a load that is in a static state. If the swing cylinder is used to compress the workpiece (Fig. 1), the torque it bears M= F●l


In the formula, M——the moment endured by the swing cylinder, N m


F——Loading force, N


l——the moment arm of the load force, m





Resistive load refers to a moving load whose inertia force can be ignored. For example, the torque exerted by the swing cylinder overcomes friction (Fig. 2a) or gravity (Fig. 2b). It is still calculated according to formula (1). The moment arm l in Figure 2a can be approximately taken as the central moment between the swing cylinder axis and the pressure wheel axis.





Inertia load refers to a moving load whose inertial force cannot be ignored. For example, the swing cylinder drives the load to swing back and forth at a certain speed. The moment it bears M=J●a


In the formula, J——moment of inertia of inertia load, kg m2


A——Suppose the angular acceleration of the load when swinging at constant acceleration,
rad/s2








where θ——rotation angle, degrees
t——Swing time through angle θ, s







2.2 Select load rate according to load properties


Load rate of swing cylinder





In the formula, M——the moment endured by the swing cylinder, N m
M0——effective output torque of the swing cylinder, N m
For static loads, η=0.9 is generally selected;for resistive loads, eta is selected between 0.2~0.5;for inertial loads, eta is selected between 0.1~0.25. The selection of eta value is related to the swing speed. If the swing speed is high, eta should be selected as a small value.












2.3 Select the use pressure
The effective output torque M0 of the swing cylinder is proportional to the operating pressure p. The M0 given on the product catalog is the value under a certain operating pressure. The operating pressure is generally 0.5MPa, but it shall not be lower than the minimum operating pressure.







2.4 Preselect nominal bore size (or model)
After estimating the torque M endured by the swing cylinder and selecting the load rate eta, the effective output torque M0 of the swing cylinder is calculated according to equation (4). From the product catalog, press M0 and the selected operating pressure p to pre-select
The nominal bore diameter (or model) of the swing cylinder.



Table 1 Comparison of characteristics of swing cylinders








Variety


Features


Swing angle


swing speed
Adjustment range
(s/90°)


allowed to suck
Collect kinetic energy
(J)


Effective loss
Output torque
(N●m)


Minimum use
Use pressure