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Toggle Mechanism (Fundamentals of Booster Mechanism)

This article is Part 5 in the Fundamentals Series. Could you move the earth using leverage? An introduction to booster mechanism with examples of how levers, toggles and crank mechanisms are used

Booster Mechanism (2): Toggle Mechanism

A toggle mechanism is a type of link mechanism consisting of 2 links and a slider. The input causes the component to move in the input direction, and the output is increased by a booster mechanism.

Toggle mechanism
Fig. 2 Toggle mechanism

Fig. 2 illustrates the toggle mechanism in which joint O is fixed, and A is not fixed but free to move.
If the force acting vertically from joint A is F0, the horizontal force acting on B when F0 is applied is F2, and assuming that the lengths of joints OA and AB are the same,

Booster Mechanism_2 is valid.

Because the tangent has the cycle shown in Figure 3 on the right, the force increases rapidly as the angle of θ/2 increases to 90°.
Thus, the closer OA and AB approach a straight line (180°), the more rapidly F2 increases.

Furthermore, when the angle θ/2 is 90°, the link becomes a straight line and the structure is very resistant to external forces even when the input is removed.

This toggle mechanism is applied to toggle clamps.

Fig. 3 Tangent graph

Booster Mechanism_3

Application of toggle mechanism Toggle clamp

A toggle clamp is a jig that clamps objects using a toggle mechanism. Please refer to Fig. 4.
Fig. 4 consists of a 4-bar linkage with A and B fixed. BC and CD are the toggle mechanism, which means that link D operates on the input from link C. This movement causes the clamping pad to clamp the corresponding part.
When locked, link C enters slightly inside the line connecting BD and locks the clamped object. Therefore, when external force is applied, link C tries to move in the direction of the red arrow, but it cannot open because the direction is opposite to the opening.
To open, link C must be moved to the open side, and this mechanism generates a large clamping pressure at the time of locking.

Fig. 4 Toggle clamp mechanism

MISUMI toggle clamp

MISUMI offers toggle clamps of various shapes, including underside holding type (vertical/horizontal handle type) and horizontal drive orientation type.

Vertical type

MISUMI toggle clamp_1