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Appendix B
Power Press Applications
Muting is allowed on power presses only during the non-hazardous portion of the
cycle (e.g. the upstroke), per OSHA1910.217, ANSI B11.1, B11.2, and B11.3. The
mute permits the insertion or removal of material into the press that would other-
wise block the sensing field of the safety light screen, causing the press to stop.
Muting should not be confused with "Inch" or "Jog" modes, whose manual
selection may bypass the safety light screen within the machine control.
For the proper application of muting on a power press, at a minimum, two (or
four) independent position switches (such as cam-operated limit switches, induc-
tive prox sensors, or pressure switches) must be used to initiate the mute during
the non-hazardous portion of the machine cycle. These position switches would
be mute devices M1/M2 (and M3/M4 if used). Typically, these switches have nor-
mally open contacts, which are held (or actuated) closed during the mute cycle.
These switches must be mounted separately to prevent misadjustment, misalign-
ment, or a single common mode failure, which would result in an improper mute
cycle or otherwise unsafe condition. They must be installed so that they can not
be easily defeated or bypassed, and their adjustment should be under superviso-
ry control.
The two (or four) muting devices must be properly adjusted (or positioned) so
that they close only after the hazard no longer exists and then open when the
cycle is complete (top of stroke) or when the hazard is again present. If improp-
erly adjusted or positioned, injury or death could result.
If the machine has reversing capability where a hazard is possible during a muted
condition, the control must include an automatic means through which muting is
permitted in the forward (non-hazardous) direction only. A "Mute Enable" signal
from the machine control, motor drive, or other machine logic, is a means to
assist in meeting this requirement.
In muting applications involving an operator, all pass-through hazards must be
eliminated so that the operator is continually detected when in the defined area.
This ensures that if a hazard arises, causing the mute cycle to end while the
operator is present, the safety light screen will immediately issue a stop. (See
pass-through hazard information below.)
A "pass-through hazard" is associated with applications that allow personnel to
pass through a safeguard, which removes or stops the hazard(s), and then allows
the individual to continue into the hazardous area. Subsequently the individual's
presence is no longer detected, and the safeguard can not prevent the start or
restart of the machine. A pass-through can be created by as little as 75 mm (3")
space between the defined area and machine frame. If the safety light screen is
muted while the individual passes through the defined area, a stop command will
not be issued and the hazard cannot be eliminated; the individual must be detect-
ed while entering the safeguarded area and the hazardous motion must stop
immediately. This is typically accomplished by supplemental safeguarding such
as described in ANSI B11 standards or other appropriate standards.
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MM-TA-12B Muting Module
Instruction Manual
WARNING . . .
Proper Installation
The user has the respon-
sibility to ensure that all local, state,
and national laws, rules, codes, and
regulations in any particular applica-
tion are satisfied. It is extremely
important to be sure that all appropri-
ate agency requirements have been
met. See Appendix C for appropriate
standards.
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