Machine Guarding Devices

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Machine Guarding Devices
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Objective

• To introduce some methods and technologies that
  can be used to reduce the exposure of employees
  to point of operation hazards.

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Goal

• The goal is to provide you with a better
  understanding of the technology that is available
  and how it is used

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Technologies

• Safety Interlock Switches
• Non Contact Interlocks
• Guard Locking Devices
• Trip Cords
• Safety Mats
• Safety edges
• Two hand trip controls
• Safety Light Curtains

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Technologies

• Safety Laser Scanners
• Enabling Switch
• Trap key Systems
• Hydraulic Press Brake Safeguarding

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Safety Interlock Switches
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Safety Interlock Switches

• Principles interlocks a guard door or access
  panel with the power source of the hazard
• Application They are used where physical hard
  guarding protects personnel from dangerous
  machine motion or other hazardous
• Advantages Provides a physical barrier that
  prevents reaching or walking into the hazardous
  area and Guards against flying chips and sparks

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Safety Interlock Switches

• Disadvantages Requires careful adjustments and
  maintenance. Inhibits access to the point of
  operation. Can reduce visibility of point of
  operation
• Cost Under 100 to over 400
• Maintenance Requires periodic testing
• Consensus Standards ANSI B11.19, 3.32, 7.1.6
  2003,

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What to look for in a safety interlock switch

• Defeat resistant The method of using the
  machine and the severity of the hazard should
  dictate how difficult it should be to override
• Reliability It must operate reliably under all
  conditions

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Defeat resistant

• Designed so they cannot be defeated in a simple
  manner. with readily available objects.

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Reliability

• The switch should be designed to operate reliably
  under all conditions such as
• Broken switch The switch should have Isolated
  contacts
• Welded contacts The switch should have positive
  mode operations

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Isolated Contacts

• On contact blocks with two sets of contacts a
  galvanic isolation barrier is required if it
  would be possible for the contacts to touch each
  other in the event of a contact weld or other
  component failure

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Isolated Contacts
Galvanic IsolationBarrier
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Over coming a welded contact

• Positive Mode Operation A moving mechanical
  component inevitably moves another component
  along with it, either by direct contact or via a
  rigid element. It should not rely solely on
  spring pressure to open the contacts

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Can they Do This?
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Standard

• This is the international symbol for a positive
  acting switch
• This is the standard the
• switch was built to

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Non-Contact Interlocks
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Non-Contact Interlocks

• Principles rely on the presence or absence of
  some sort of magnetic or electronic field
• Application They are used where conditions make
  it difficult or imposable to use a mechanical
  switch
• Advantages They can be used in harsh or wet
  environments, they do not require careful
  alignment

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Non-Contact Interlocks

• Disadvantages switches without redundancy and
  automatic monitoring are generally not suitable
  for interlocking duties. Require a controller
• Cost Under 250 to over 800 (with controller)
• Maintenance Requires periodic testing
• Consensus Standards ANSI B11.19, 3.32, 7.1.6
  2003,

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What to look for in a non contact interlock
switch

• Defeat resistant The method of using the
  machine and the severity of the hazard should
  dictate how difficult it should be to override
• Reliability It must operate reliably under all
  conditions

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Defeat resistant

• By using multiple magnetically biased reed
  contacts, or an electrically coded read head
  intentional defeat is drastically reduced.

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Difficult to use a mechanical switch
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Typical non-contact interlocks
Control Monitor Relay
Electrically Coded
Magnetically Coded
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Reliability

• These devices rely on the presence or absence
  of some sort of magnetic or electronic field.
  Because they do not have the benefit of true
  mechanical positive mode operation, they must
  rely on oriented failure modes and/or the use of
  duplication and monitoring

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Guard Locking Devices
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Guard Locking Devices

• Principles The guard remains closed and locked
  (retaining the actuator) until the risk of injury
  from the hazard has passed, to insure that no
  entry can be made to the hazardous area until all
  motion has ceased
• Application used in applications where dangerous
  motion behind a panel or door will continue for
  some period of time after power is removed from
  a machine
• Advantages They can be used on machines with
  long stopping times.

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Guard Locking Devices

• Disadvantages Needs a method to detect the
  stopping of motion or a safety rated timer.
• Cost Under 150 to over 700
• Maintenance Requires periodic testing
• Consensus Standards ANSI B11.19, 3.32, 7.1.6
  2003,

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What to look for in a Guard Locking Device

• In a Conditional Guard Unlocking Device- That it
  can only be opened on Receipt of a Signal That
  the contactor is OFF or a pre set time interval
  has elapsed or that dangerous motion has ceased.
• In an Unconditional Guard Locking device That
  he handle or guard lock also opens the circuit
  and that a sufficient amount of time is required
  to enable the motion to stop

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Guard Locking

• Locking Family Switches are typically used in
  applications where dangerous motion behind a
  panel or door will continue for some period of
  time after power is removed from a machine

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Guard Locking

• The guard remains closed and locked (retaining
  the actuator) until the risk of injury from the
  hazard has passed, to insure that no entry can be
  made to the hazardous area until all motion has
  ceased

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Four Types of Guard Locking

• Manually Applied/Manually Released
• Spring Applied/Power Released
• Power Applied/Spring Released
• Power Applied/Power Released

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Manual
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Power Type Switches
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Solenoid operated locking switch
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Guard Locking

• Spring applied, power release devices must
  have manual unlocking that requires the use of a
  tool to operate.

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Manual unlocking
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Trip Cords
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Trip Cords Rope or Wire pulls

• Principles when pulled or cut (made slack) will
  cause the attached switch to generate an
  emergency stop
• Application They are used horizontally across
  the points of hazard generated by rotating
  machinery, conveyor motion etc.
• Advantages they can be located at the point of
  hazard for the involved operators use, unlike an
  E-Stops which may be located away from the point
  of hazard

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Trip Cords

• Disadvantages They do not prevent injury, but
  may limit the extend of injury, can have zones of
  unknown action
• Cost Under 250 to over 500
• Maintenance Requires periodic testing, need to
  be kept in tension
• Consensus Standards ANSI B11.19, 3.32, 7.1.6
  2003,

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What to look for in trip cord

• Proper Tension The unit should be designed to
  be under constant steady tension. To slack or to
  tight should trip the device
• Proper Installation It must be installed to
  minimize the unknown action zone

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Proper Tension
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Proper Installation
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Proper installationVector Eyebolt
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Vector Eyebolt
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Distance between Eyebolts
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Direction Change
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Turning the corner
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Turning the corner
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When Properly Installed

• The switch should activate with reasonable force
  (5 to 20 lbs.) and reasonable deflection (3 to 6
  inches) over the zone of protection

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Safety Mats
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Safety Mats

• Principles A signal is transmitted through the
  upper and lower plates. When sufficient pressure
  is applied to the mat the plates touch causing
  the controller to send a stop signal to the
  machine.
• Application They are used where perimeter access
  guarding is required protects personnel from
  dangerous machine motion or other hazardous
• Advantages Provides improved productivity while
  providing access guarding.

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Safety Mats

• Disadvantages Requires a controller to monitor
  the status of the mats, may need frequent
  replacing if in areas of heavy vehicle traffic
• Cost Under 700 to over 5,000
• Maintenance Requires periodic inspection and
  testing
• Consensus Standards ANSI B11.19-2003
• ANSI/RIA R15.06-1999

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What to look for in a safety mat

• Mat Controller- A controller is necessary to
  monitor for a failure in the mat system.
• Proper Installation Most important is the
  calculation of the safety distance. To insure a
  minimum mat size is placed between a worker and
  the hazard, and that the mat is secured to the
  floor

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Mat Controller
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Typical Application
Pressure Sensitive Safety Mats
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Mat Safety Distance Calculations

• The first and by far the most important
  consideration is the calculation of the safety
  distance. There is a Minimum mat size that should
  be placed between a worker and a Hazardous motion.

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ANSI B11.19-2003Annex D

• The added distance, in inches for a ground level
  device which can be reached over (safety mats) is
• 48 inches

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DsK (TsTcTrTspm)Dpf
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• K 63 in./sec (hand speed constant)
• Ts Tc 0.200 (Total machine stop time)
• Tr 0.030 (mat control system 30ms)
• Tspm .050 (A brake monitor set of .250
  seconds - .200 total stop time)
• Dpf 48 in

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DsK(TsTcTrTspm)Dpf

• Ds63(.200.03.05)48
• DS65.64 in.

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65.64
K(TsTcTrTspm)17.64
48
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Only authorized persons may relocate the safety
mat
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Safety Edges
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Safety Edges

• Principles The safety contact is located inside
  the safety contact strip. Pressing the safety
  contact strip will cause the controller to change
  to an open state, but when pressure is removed
  the contacts will NOT transfer back without a
  reset
• Application flexible edging strips fixed to the
  edge of a moving part. If the moving part
  strikes the operator (or vice versa) a stop
  signal is sent
• Advantages can be used where there is a risk of
  crushing or shearing, or a risk of operator
  entanglement.

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Safety Edges

• Disadvantages Requires a controller to monitor
  the status of the edges, can only be used on
  machine with short stop times , or to limit the
  extent of an injury
• Cost Under 600 to over 1,000
• Maintenance Requires periodic inspection and
  testing
• Consensus Standards ANSI B11.19-2003 3.59

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What to look for in a safety edge

• Edge Controller- A controller is necessary to
  monitor for a failure in the mat system.
• Proper Installation The switch edge should be
  of sufficient size to insure that the switch will
  activate and stop motion before the edge is fully
  compressed

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Safety Contact Strips

• Safety contact strips are used on edges of guard
  or gates and at possible crushing or shearing
  points

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How they work
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Two Hand Trip/control
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Two Hand Control/Trip

• Principles Two start buttons have to be operated
  at the same time to run the machine. This ensures
  that both hands of the operator are occupied in a
  safe location and cannot be in the hazard area
• Application They are common on single cycle and
  index table applications
• Advantages Can provide effective protection for
  the operator, Two-hand trip can be used on
  machines that cannot be stopped

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Two hand control/Trip

• Disadvantages Provides protection for the
  operator only, Inefficient because the operators
  hands must maintain the buttons through the
  hazardous portion of the cycle
• Cost Under 400 to over 600
• Maintenance Requires periodic inspection and
  testing
• Consensus Standards ANSI B11.19-2003 3.71 3.73

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What to look for in a Two hand control/Trip

• Mounting separation the installation should be
  such that the two controls cannot be operated
  with the hand and elbow from the same arm. The
  device shall be located at a distance such that
  the operator cannot reach the hazard with a hand
  or other body part before the hazard is removed.
  
• Synchronous Actuation/Simultaneity An output
  signal shall be generated only when both buttons
  are actuated within .5 seconds of each otherif
  not, both must be released before the next output
  signal can occur.

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Two Hand Control Relay
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Two-Hand Control
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Safety Light Curtains
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Safety Light Curtain

• Principles A photoelectric transmitter projects
  an array of synchronized, parallel infrared light
  beams to a receiver unit. When an opaque object
  interrupts one or more beams the control logic of
  the light curtain sends a stop signal to the
  guarded machine
• Application They are very often used for point
  of operation guarding and for perimeter guards
• Advantages Protects multiple operators and
  other employees, Allows freer movement for
  operator, No adjustments required

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Safety Light Curtain

• Disadvantages Not practical for machines with
  long stop times, Does not protect against flying
  chips and sparks, Does not protect against
  mechanical failure
• Cost Under 1000 to over 7000
• Maintenance Requires periodic inspection and
  testing (once per shift)
• Consensus Standards ANSI B11.19-2003 3.44
  ANSI/RIA R15.06-1999, UL508

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What to look for in aSafety Light Curtain

• Proper Installation- The curtain must be at the
  proper distance from the hazard, and installed in
  such a manner that you can not stand between it
  an the hazard without being detected the light
  curtain or other device.
• Supplemental Guarding- May be needed to prevent
  reaching over under or around the Safety Light
  Curtain

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Safety Light Curtains
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A Light Curtain in its Simplest Form
Receiver
Emitter
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Safety Light Curtain Design

• Redundant Logic Systems
• Dissimilar microcontrollers
• Unique software for each controller
• Written by different authors
• Comparison of Status
• Exercising of System Components

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Safety Light Curtain
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Optical Performance

• The presence sensing device shall have an
  identifiable minimum object sensitivity.
• Not Beam Spacing

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Minimum object sensitivity

• This refers to the smallest object (diameter)
  that the light curtain can detect. It is
  sometimes referred to as the resolution of the
  light curtain or as its detection capability

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Beam Spacing, or Optical Pitch

• Refers to the distance from the center line of
  one beam to the center line of the next beam
• It is possible for an object that is the same
  diameter as the optical pitch to be in such a
  position that it does not block the path of a
  single beam

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Some Common light curtain resolutions

• 14mm or less (0.55 inches) for finger
  protection
• 30mm or less (1.25 inches) for hand protection
• 50mm 500mm or less (2.00 20.00 inches) for
  body protection

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Three Box System
Two Box System
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Type 2 VS, Type 4

• Fault Detection Circuits Type two light
  curtains lack the redundant automatic
  self-checking circuits employed in type 4 light
  curtains. As a result they do not meet the OSHA
  or ANSI requirements for control reliability
• Optical Angle- Type 4 safety light curtains have
  an effective optical angle of 2.5º, while type 2
  devices have an effective optical angle of 5º.
  The wider angle increases the possibility of
  reflective surface interference which may cause
  an optical short circuit

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Optical Short Circuit
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Test Procedure
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Safety Laser Scanners
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Safety Laser Scanner

• Principles Safety laser scanners are optical
  sensors that used pulsed laser light to scan its
  surroundings. It then compares the scanned
  information to its predefined zones. If it
  detects an intrusion into that area it sends a
  stop signal to the guarded machinery
• Application Robotic work cells, in front of
  press or other machinery, and guarding the front
  or rear of an automated guided vehicle
• Advantages Can guard stationary and moving
  equipment, and can be configured for multiple
  irregularly shaped hazardous areas. Can provide a
  warning Zone

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Safety Laser Scanner

• Disadvantages Does not protect against flying
  chips and sparks, Does not protect against
  mechanical failure, May not work in very dusty or
  Smokey environments
• Cost Under 4500 to over 8000
• Maintenance Requires periodic cleaning and
  inspection and testing.
• Consensus Standards ANSI B11.19-2003 3.44
  ANSI/RIA R15.06-1999, 11.5

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What to look for in aSafety Laser Scanner

• Warning and Protected Zones Clearly Marked- The
  Zones should be clearly marked to give persons in
  the area a clear indicator of the location of the
  zones.
• The System is Installed Properly- The units
  should not be more than 12 above the walking
  surface when mounted horizontally

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Laser Scanners

• Are opto-electronic protective device that
  operates similar to radar, but using light
  transit time to measurer its environment
• The time of flight measurement is directly
  related to the distance the light has traveled to
  an object

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Trap Key / Captive Key Systems
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Trap Key System

• Principles the premise that no one key can be in
  two places at once, Trap key systems can be
  configured to require a predetermined sequence of
  events takes place to eliminated or reduced
  hazards to a tolerable level before operators are
  exposed to them
• Application Robotic work cells, to prevent the
  accidental or illegal discharge of processing
  material, to control access to equipment or
  machinery while it is in a dangerous state
• Advantages Can be used in an explosive
  atmosphere, Can provide a higher degree os
  security and tamper resistance

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Trap Key Systems

• Disadvantages May not be best for machines that
  require frequent manual operation, may requires
  additional hard guarding
• Cost Under 1,100 to over 15,000
• Maintenance Requires periodic cleaning and
  inspection and testing.
• Consensus Standards ANSI B11.19-2003 3.44
  ANSI/RIA R15.06-1999, 5.2.1

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What to look for in a Trap Key System

• The lock can only be operated by the dedicated
  key It should not be possible to defeat the
  lock by means of a tool or by mistreating it in
  any manner, and the specifying of the key code
  should insure that only one key works.
• It is not possible to obtain the key in any other
  manner than the intended manner Any excessive
  force will result in a broken key as opposed to a
  broken lock

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Time Delay Trap Key
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Non Time Delay Example
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Dual Key Lock
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How it works
B Key
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3-Port Spool Valve
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Valve Interlock
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Enabling Switch Device

• Principles- A manually operated device which when
  continuously activated, permits motion
• Application- Allows for troubleshooting, set-up,
  programming, or servicing of robotic or automated
  machinery
• Advantages- Provides the margin of safety needed
  when no other safety devices are possible or
  practical

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Enabling Switch Device

• Disadvantages Requires the use of one hand to
  control the switch, may cause fatigue if used for
  long periods
• Cost Under 300 to over 500
• Maintenance Periodic inspection of switch and
  cable, testing of device
• Consensus Standards ANSI/RIA R15.06-1999, 3.12
  10.10.3

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What to Look for

• Ergonomic Design Switch should be designed to
  minimizes discomfort and allow the hand to be in
  as much of an at rest position as possible
• That the switch is used in conjunction with some
  other presence-sensing safeguarding device to
  ensure the safety of others in the area

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Enabling Device
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• Position 1 This is the released STOP position
• Position 2 This is the ENABLED position, the
  trigger is pressed and held in this position to
  allow machinery to operate
• Position 3 This is Squeezed STOP position, the
  trigger is pressed beyond the middle position

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Laser Safeguardingfor Hydraulic Press Brake
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Laser Safeguardingfor Hydraulic Press Brake

• Principles- A continuous band of laser light that
  senses the zone below the punch. If an
  obstruction is detected, the ram movement is
  stopped and retracted
• Application- For use on most down and up acting
  hydraulic press brakes
• Advantages- Permits freedom of handling the
  workpiece and higher throughputs while providing
  operator protection and real time monitoring for
  press brake failures

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Laser Safeguardingfor Hydraulic Press Brake

• Disadvantages Will not work on all Hydraulic
  press brakes, requires professional installation
• Cost 9,000 to 15,000 installed
• Maintenance Requires periodic inspection and
  testing
• Consensus Standards ANSI B11.19, UL 1998, EN954-1

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What to look for

• Failure detection Should be performed by
  real-time monitoring of the process under control
• Third party Certification The system should be
  inspected an certified by a third party such as a
  NRTL or a EU Notified Body

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Laser Scanning System
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System in Use
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Summary
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Questions?
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Thank You