Two-hand control

The two-hand control (colloquially also two-hand operation ) is a protective device for machines. It is mainly used to protect hands and arms against mechanical hazards from crushing, shearing or being drawn in.

Working principle

To trigger the dangerous movement, e.g. B. the working stroke of a press, both controls must be operated simultaneously with the hands. When one of the control elements is released, the movement is stopped or - if this does not pose a risk - the direction of movement is reversed. This ensures that the hands are outside the danger area, namely on the operating elements, during the dangerous movement. An operation of both control elements with one hand or with other parts of the body is prevented by a sufficient distance, partitions or other structural measures.

The disadvantage of two-hand controls is that the operator cannot perform any other activities while actuating the control elements. If you let go of a control element prematurely, bad parts or malfunctions can occur. In principle, a two-hand control only protects the person who operates it.

Classification and requirements according to DIN EN 574

The following parts of this section seem since November 2019 out of date to be : The new standard DIN EN ISO 13851: 2019-11 "Safety of machinery - Two-hand control devices - Functional aspects and design guidelines" has replaced DIN EN 574.
Please help with the missing information to research and insert .

Two-hand controls have to meet different requirements depending on the risk to be covered. Several types of two-hand circuits are therefore defined in EN 574. Certain basic requirements apply to all types:

• it must be operated with both hands
• the control output signal may only be present as long as both control elements are operated. The output signal may then only be generated again after releasing both control elements.
• if one of the control elements is released, the output signal must be terminated
• accidental activation and bypassing of the protective device must not be possible

Further requirements depend on the type of two-hand control selected

• Type I: Application of category 1 according to DIN EN 954-1 (i.e. usually single-channel design).
• Type II: Use of category 3 according to DIN EN 954-1 (single-fail-safe, usually two-channel design)
• Type IIIA: both control elements must be actuated synchronously within 0.5 s, category 1
• Type IIIB: both control elements must be actuated synchronously within 0.5 s, category 3
• Type IIIC: both control elements must be actuated synchronously within 0.5 s, category 4 (even an accumulation of up to 3 errors does not lead to failure of the safety function)

Controls

Electric buttons or manually operated pneumatic valves are often used as operating elements, occasionally also operating levers (for example in hydraulic tail lifts to select the direction of movement) or other operating elements. Individual manufacturers use novel operating principles such as capacitive buttons.

Pre-assembled two-hand control panels are available which, in addition to two buttons and standard partition walls, contain an emergency stop button.

control

In order to meet the requirements with regard to the category according to DIN EN 954-1, the control components and actuators used must also be designed accordingly.

Special two-hand control devices are available as logic modules; in the case of more complex controls, the function of the two-hand control is mapped by a programmable safety control. Many suppliers have tested function modules for two-hand controls for programmable safety controls.

Pneumatic presses use type II, IIIB and IIIC pneumatic press safety valves, which combine the function of a logic module and actuators. The control is possible through manually operated pneumatic valves or electrically.

exam

Two-hand controls must be checked annually by a competent person. The follow-up time is also measured, i.e. the time in which the dangerous movement comes to a standstill after a control element has been released.

Regulations

• DIN EN 574: 2008 Safety of machines - two-hand controls - functional aspects - design principles (for the European Union)
• ZH 1/456 "Safety rules for two-hand controls on power-operated presses in metalworking" (valid for presses in old machines)

Individual evidence

1. ↑ Note: As of 2013, DIN EN 574 still uses the terms of DIN EN 954-1, not the applicable DIN EN ISO 13849-1