Title: Machine Guarding Devices
1Machine Guarding Devices
2Objective
-
- To introduce some methods and technologies that
can be used to reduce the exposure of employees
to point of operation hazards.
3Goal
-
- The goal is to provide you with a better
understanding of the technology that is available
and how it is used
4Technologies
- Safety Interlock Switches
- Non Contact Interlocks
- Guard Locking Devices
- Trip Cords
- Safety Mats
- Safety edges
- Two hand trip controls
- Safety Light Curtains
5Technologies
- Safety Laser Scanners
- Enabling Switch
- Trap key Systems
- Hydraulic Press Brake Safeguarding
6Safety Interlock Switches
7Safety 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
8Safety 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,
9What 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
10Defeat resistant
- Designed so they cannot be defeated in a simple
manner. with readily available objects.
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14Reliability
- 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
15Isolated 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
16Isolated Contacts
Galvanic IsolationBarrier
17Over 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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19Can they Do This?
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22Standard
- This is the international symbol for a positive
acting switch - This is the standard the
- switch was built to
23Non-Contact Interlocks
24Non-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
25Non-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,
26What 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
27Defeat resistant
- By using multiple magnetically biased reed
contacts, or an electrically coded read head
intentional defeat is drastically reduced.
28Difficult to use a mechanical switch
29Typical non-contact interlocks
Control Monitor Relay
Electrically Coded
Magnetically Coded
30Reliability
- 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
31Guard Locking Devices
32Guard 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.
33Guard 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,
34What 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
35Guard 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
36Guard 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
37Four Types of Guard Locking
- Manually Applied/Manually Released
- Spring Applied/Power Released
- Power Applied/Spring Released
- Power Applied/Power Released
38Manual
39Power Type Switches
40Solenoid operated locking switch
41Guard Locking
- Spring applied, power release devices must
have manual unlocking that requires the use of a
tool to operate.
42Manual unlocking
43Trip Cords
44Trip 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
45Trip 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,
46What 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
47Proper Tension
48Proper Installation
49Proper installationVector Eyebolt
50Vector Eyebolt
51Distance between Eyebolts
52Direction Change
53Turning the corner
54Turning the corner
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56When 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
57Safety Mats
58Safety 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.
59Safety 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
60What 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
61Mat Controller
62Typical Application
Pressure Sensitive Safety Mats
63Mat 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.
64ANSI B11.19-2003Annex D
- The added distance, in inches for a ground level
device which can be reached over (safety mats) is - 48 inches
65DsK (TsTcTrTspm)Dpf
66- 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
67DsK(TsTcTrTspm)Dpf
- Ds63(.200.03.05)48
- DS65.64 in.
6865.64
K(TsTcTrTspm)17.64
48
69Only authorized persons may relocate the safety
mat
70Safety Edges
71Safety 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.
72Safety 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
73What 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
74Safety Contact Strips
- Safety contact strips are used on edges of guard
or gates and at possible crushing or shearing
points
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76How they work
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78Two Hand Trip/control
79Two 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
80Two 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
81What 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.
82Two Hand Control Relay
83Two-Hand Control
84Safety Light Curtains
85Safety 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
86Safety 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
87What 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
88Safety Light Curtains
89 A Light Curtain in its Simplest Form
Receiver
Emitter
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91Safety Light Curtain Design
- Redundant Logic Systems
- Dissimilar microcontrollers
- Unique software for each controller
- Written by different authors
- Comparison of Status
- Exercising of System Components
92Safety Light Curtain
93Optical Performance
- The presence sensing device shall have an
identifiable minimum object sensitivity. - Not Beam Spacing
94Minimum 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
95Beam 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
96Some 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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98Three Box System
Two Box System
99Type 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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101Optical Short Circuit
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103Test Procedure
104Safety Laser Scanners
105Safety 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
106Safety 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
107What 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
108Laser 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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114Trap Key / Captive Key Systems
115Trap 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
116Trap 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
117What 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
118Time Delay Trap Key
119Non Time Delay Example
120Dual Key Lock
121How it works
B Key
1223-Port Spool Valve
123Valve Interlock
124Enabling 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
125Enabling 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
126What 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
127Enabling Device
128- 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
129Laser Safeguardingfor Hydraulic Press Brake
130Laser 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
131Laser 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
132What 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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134Laser Scanning System
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136System in Use
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138Summary
139Questions?
140Thank You