Two-handed control devices

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. 

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. 

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

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

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... 

Selection of safeguards to allow for safe access to the danger zone during normal operation, e.g. interlocking guard, two-hand control device... 

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. 

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). 

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 ... 

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. 

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

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. 

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. 

FIGURE 32.18 Schematic of the prehension patterns of the hand as defined by Keller, Taylor, and Zahn (1947) (al) palmar prehension (three-jaw chuck), (o2) palmar prehension (two finger), (b) tip prehension, (c) lateral prehension, (<0 hook prehension, (e) spherical prehension, (/) cylindrical prehension. In a handlike prosthesis, it takes two to four independently controlled degrees of freedom to implement these prehension patterns. In a non-hand-like device, a single-degiee-of-free-dom device such as a split hook can be used. 

A machine will have a presence-sensing device and an interlocking barrier gate. How far should you locate a two-hand trip control from the point of operation ... 

Walkie Tractors. Walkie tractors are the smaller variety of indnstrial tractors.These tractors are battery-electric with motive power, braking, and steering being provided by a single wheel or a close-coupled pair of wheels. The drive mechanism is tiller-controlled through hand controls, as in other walkie eqnipment, and deadman controls are provided.Two other wheels are provided for stability at the rear of the vmit. A variety of coupling devices are available for attaching the tractor to trailers and semilive skids. 

Each bay is responsible for (dis)connecting one element from the transmission network. This is achieved by a set of elements - relays and electronic devices of the following two types - either a protection device or a control device. The function of the protection devices is to disconnect the power elements from the transmission network, e.g. as a result of overloading of a line or of a generator. The control devices, on the other hand, are used to connect or disconnect the power elements from the network and are typically used by either the operators in the respective control centres or by special purpose software (SPS) designed to undertake some of the operators functions automatically. 

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