Two-hand control can be used as a safeguarding device in the single-stroke mode of operation on part-revolution clutch presses and hydraulic press and press brakes.
There are many requirements that must be met before two-hand control can be used as a point-of-operation safeguard. These requirements are located in OSHA 29 CFR 1910.217 and ANSI B11.1, B11.2, B11.3, and B11.19. We have referenced the following paragraphs for your convenience:
(c)(3)(i) Point-of-operation devices shall protect the operator by:
(e) Requiring application of both of the operator’s hands to machine operating controls and locating such controls at such a safety distance from the point of operation that the slide completes the downward travel or stops before the operator can reach into the point of operation with his hands;
(c)(3)(vii) The two-hand control device shall protect the operator as specified in paragraph (c)(3)(i)(e) of this section.
(a) When used in press operations requiring more than one operator, separate two-hand controls shall be provided for each operator, and shall be designed to require concurrent application of all operators’ controls to activate the slide. The removal of a hand from any control button shall cause the slide to stop.
(b) Each two-hand control shall meet the construction requirements of paragraph (b)(7)(v) of this section.
(c) The safety distance (Ds) between each two-hand control device and the point of operation shall be greater than the distance determined by the following formula:
Ds = 63 inches/second x Ts where:
Ds = minimum safety distance (inches);
63 inches/second = hand speed constant; and
Ts = stopping time of the press measured at approximately 90° position of crankshaft rotation (seconds).
(d) Two-hand controls shall be fixed in position so that only a supervisor or safety engineer is capable of relocating the controls.
(b)(7)(v) Two-hand controls for single stroke shall conform to the following requirements:
(a) Each hand control shall be protected against unintended operation and arranged by design, construction, and/or separation so that the concurrent use of both hands is required to trip the press.
(b) The control system shall be designed to permit an adjustment which will require concurrent pressure from both hands during the die closing portion of the stroke.
(c) The control system shall incorporate an antirepeat feature.
(d) The control system shall be designed to require release of all operators’ hand controls before an interrupted stroke can be resumed.
The following formula is used to compute the minimum safety distance (Ds) on mechanical power presses to meet the ANSI (American National Standards Institute) B11.1 press safety standard:
Ds = K x (Ts + Tc + Tr + Tspm) where:
K = Hand speed constant (63 inches/second)
Ts = Stop time of equipment measured at the final control element
Tc = Response time of the control system
Tr = Response time of the two-hand control device and its interface
Tspm = Additional time allowed for the stopping performance monitor to compensate for variations in normal stopping time
Dpf = The added distance due to the depth penetration factor. Note: If the channel blanking feature is used on light curtains, additional safety distance must be enforced based on the number of channels blanked.
When determining the safety distance, a portable or built-in stop-time measuring unit must be used to check the stopping time (Ts) of the machine.
ALL-IN-ONE TWO-HAND CONTROL
An all-in-one two-hand control is available that includes a prewired control box that is ready for the user to bring wires in from the machine actuator.