Trigger (finger clench grip)

The European Standard EN894-3 defines manual control actuator as: a control actuator adjusted or manipulated by human hand to effect change in a system, e.g., push-button, knob, steering wheel.

The trigger can be categorized from its movement characteristics:

• Type of movement: rotary
• Axis of movement: x (right hand rule)
• Direction of movement: one per axis
• Continuity of movement: Discrete
• Angle of rotation for continuous rotary movement less than 180°

From its grip characteristics:

• Type of grip: clench
• Part of hand applying force: finger(s)
• Method of applying force: tangential

For more information about the definitions and usage of the above read EN894-3.

The minimum recommended dimensions for the trigger according to the above characteristics are:

Width of grip ≥15mm
Length of grip along axis of rotation must be between 60≤ and ≤80 mm.
Maximum recommended actuating force 15Nt if the operator hand stays still and 30Nt if the hand is moving. For example if the grip is a trigger (1 or 2 fingers max) in a hand clench the maximum recommended actuating force will be 15Nt, if the grip is part of a lid safety lock then the force will be 30Nt.

A well designed finger clench grip must have enough space for 2 fingers, must not hurt them or make the operator discomfort during operation. The figure above gives basic dimensions of a functional trigger design (tooling). It’s easy to remember as the 30-40-10-40 trigger (30mm inner diameter, 40mm outer, 10mm vertical center distance and 40mm overall length). The angle of 34.32° and the radius of 60 and 80mm include the geometrical place of the rotation axis center for maximize actuating torque. In other versions of the trigger the outer diameter is removed and only the contact surface of inner diameter remains.