Two hand control

Two—Hand Controls-Requires the operator to use both hands concurrently to activate the machine. 

B2 Standards. These apply to particular safety devices or components such as EN 574 (Two Hand Controls) and EN 60947 (Safety Switching Devices). 

Safety components, as opposed to critical components, fulfill a specific safety function when in use and the failure or malfunctioning of the device places exposed persons in imminent danger. Safety components are regulated by the Machinery Directive and examples inelude light eurtains, two-hand controls, and sensor mats. 

Safety components such as light curtains, sensor mats, and two-hand controls are regulated by Machinery Directive 89/392/EEC which requires a manufacturer s declaration of conformity but no CE marking. EU type-approval marks are also highly recommended for safety components. 

A term used in American National Standards Institute (ANSI) standards to describe any actuating control device or mechanism that prevents the operator from reaching the hazard point during normal cycling of the machine. A two-hand-control device is an example of a hostage control device. See also Two-Hand Controls. 

The minimum distance from each control-actuating device of a two-hand control system to the hazard point such that the operator cannot reach the hazard point with a hand or other body part before cessation of motion of the hazardous portion of the machine cycle. See also Separation Distance (Safety Light Screen). 

Tripping devices for a machine that require simultaneous application of both hands to operate the control, so that the hands of the operator are kept out of the point-of-operation area while the machine is operating. A two-hand-control device protects only the hands of the machine operator (and not other individuals) when used as a safeguarding device. See also Hostage Control Device. 

On some special purpose machines such as guillotines with photo-electric safety devices or loose knife cutting machines, additional protection is provided by two-hand control ... 

Multiple Operators Use of more than one person can provide redundancy. In aircraft, a pilot and a copilot can perform the same function. If one is incapacitated, the other can take over (parallel redundancy). Another example (series redundancy) might be atwo-person press. Both operators may face the hazard of getting caught in the machine when it is in motion. If each operator has a two-hand control, all four hands of the operators must depress the switches before the machine will operate. 

There are many kinds of point-of-operation devices. They include gates or moveable barrier devices, presence sensing devices, pull-out devices, sweep devices, hold-out or restraint devices, two-hand controls, and hand-feed tools. 

Distance and Time The two-hand control must be far enough from the machine so one cannot reach into the point-of-operation after the machine starts in motion. Equation (13-1) would apply here as well. 

Figure 13-14. Example of a two-hand control device on a press. (From OSHA 3067.)...

Presence sensing devices Two-hand controls Awareness Means... 

Use four-way, spring-centered, pneumatic valves for equipment working off of two hand controls. 

Two-hand controls are used on machines on cyclic operations where the work is placed in the machine and the machine struck on. They are applicable only to machines with a single operator and the control buttons must be positioned more than a hand-span apart. The control circuit should be arranged so that both controls must be activated simultaneously to start the cycle and that both controls must be released after each cycle before the next cycle can be initiated. Release of either button during the dangerous part of the cycle must stop or reverse the machine movement. 

Safety controls use involvement of the operator as a safeguarding method, and include safety trip controls, two-hand controls, and two-hand trips. For safety trip controls, if the operator or anyone trips, loses their balance, or is drawn toward a machine, the resulting pressure applied to a bar installed on the machine will stop the operation. The positioning of the bar, therefore, is critical. It must stop the machine before a part of the employee s body... 

Another type of safety control is the two-hand control, which requires constant concurrent pressure by the operator to activate the machine. This kind of control requires a part-revolution clutch, brake, and a brake monitor if used on a power press. With this type of device, the operator s hands must be at a safe location (on control buttons) and at a safe distance from the danger area while the machine completes its closing cycle. The advantages of this type of safety control are that the operator s hands are at a predetermined location and that the operator s hands are free to pick up a new part after the first half of a cycle is completed. Some two-hand controls, however, can be rendered unsafe by using an arm on the controls or blocking, thereby permitting one-hand operation. The safety control only protects the operator. 

Figure 12.16 Pedestal mounted free-standing two-handed control device.

Where two-handed controls are used, the following principles must be followed ... 

Hold-to-run controls give even less protection to the operator than two-handed controls and have the same main drawback in that they give no protection to anyone other than the operator. 

British Standards Institution, BS EN 574 (ISO 13851), Safety of machinery - Two-hand control devices - Tunctkmal aspects - Principles for design, BSI, London (1996)... 

Electrical parts of machinery Interlocking devices associated with guards Electrosensitive protective equipment Emergency stop devices Two hand control devices... 

Other machine features that offer protection include moveable barriers, automatic feed systems, presence-sensing devices, emergency stop control, hand control devices and mechanisms, such as pull-out devices, restraint devices, and two-hand control. Reduced speed control is used during setup, cleaning, and maintenance. Other safety mechanisms include antikickback devices, run controls, and foot controls. 

The majority of the instructions for controlling the robot and other equipment such as the rotating tables, access door latches and the response to limit switches and the "two hand" controls etc, is programmed... 

Pure safety function pure (e.g., two-hand control with dependable stopping of the drives) and a... 

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