Download Lecture #2: Robot Safety Robotic Operation: Module #1

Lecture #2: Robot Safety
Robotic Operation: Module #1
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Safety: Robot operation within a work cell.
Powering up a robot controller.
Safety concerns on powering down a robot controller.
Explain how to power up/down a robot’s controller.
Cover Robot Safety Organizations.
Safety Organizations:
o OSHA
1970.
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OSHA has no specifics on robot safety.
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OSHA only addresses safety around machinery, which emphasis machine
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guards.
o ANSI/RIA
Two organizations have created standards for working around robots.
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American National Standard Institute (ANSI)
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Robotic Industries Association RIA
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Both organizations have created two standards that relate to integrated
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manufacturing systems.
- Safeguarding a work cell:
o Safe guarding devices:
Primary function of the device is to provide a warning and to restrict traffic
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flow.
A work cell should have three zones: OVERHEAD figure 10-1
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 Zone 1: Area outside work zone which has no restrictions on human
traffic.
 Zone 2: Area inside of work cell but out of reach of robot’s work
envelope.
 Zone 3: Area inside robot’s work envelope.
 Zone 1: Usually consist of signs and yellow lights.
 Zone 1 to 2: Physical barrier with electrical interlocks.
 Zone 3: Floor outline indicating robots reach.
o Safety Hardware:
Physical barriers can consist of:
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 Chains and guard post
 Safety rails
 Wire mesh fencing
 Equipment in the work cell, such as electrical panels.
Sensing Devices
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 Light curtains
 Pressure sensing floor pads.
 Proximity sensing devices.
 Look over SICK proximity sensor, figure 10-3. OVERHEAD
 These devices will automatically warn and shut down equipment
E-Stop Devices
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 Red mushroom push buttons that will kill power to machinery.
 Should always be hard wired and not computer or PLC controlled.
 E-Stop/Jog stations should always be in view of motor it controls.
Interlocks:
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 Door switches
 Should disable outputs that control motors, relays, solenoids.
o Proximity Sensing Devices
Two types: Ultrasonic and laser units are used to sense presence of a human.
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Lasers provide the best detection.
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o Light Curtains
Light curtains are also referred to as light screens or optical guards.
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Device transmits an array of parallel light beams to a receiver.
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Light type is infrared.
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Light curtain is equivalent to a direct type photo eye.
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Receivers are designed to detect light source at a specific frequency and
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ignores all other external light.
o Safe Curtain Distance:
Distance detection curtain must be mounted from machine’s pinch point so
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that the curtain can halt the machine before any part of operator’s body
makes contact with machine.
Safe Distance = Body Speed x (Stop time of mach + Response time of
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machine controls to activate brake + Response of safety curtain + Brake stop
time) + Distance of non detectable body parts.
Body speed is defines by hand movement.
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ANSI standard body speed value is 63 inches per second. (3.57 miles/hour)

Stop Time of Machine: Measures from final de-energized control element.
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Response Time: Time required for controls to activate machine.
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Sensor Response: Detection time of light curtain.
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D = K x (Ts + Tc + Tr + Tbm) + Dp
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o Sensing Mats
Simple solution

Normally open switch.
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o Interlock Devices:
Interlocks machine guard door with power source.

Interlock Switch Operation:
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 Must be reliable under extreme conditions and rough treatment.
 Must be designed so that mechanism cannot be cheated or defeated.
 Best if device is not accessible when guard is open.
o Interlock Positive Mode Operation:
A force is required to break electrical contact.
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Negative, requires no force to break electrical contact.
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o Forms of Interlock Devices
Power interlocking:
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 Direct electrical contact with machine power.
 Switch must be capable of handling high currents and voltage.
 Not common with three phase systems.
Control Interlocking:
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 Most common method used.
 Contacts are wired in with low voltage control circuit.
o Calculating Safe Guard Distance:
S = (k x T) + C
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 S ~ Minimum distance from danger zone to opening of guard edge.
 K ~ Approach speed of operator. 1600mm/sec = 5.25 ft/sec = 3.57
miles/hour
 T ~ Total time of interlock switch opening to machine stopping.
 C ~ Distance operator can reach past guard before stopping action
occurs.
o Mechanical Interlock Switches:
Links movement in guard door to positive mode switch operation.

 Actuated: Tongue on guard makes physical contact with switch
contacts.
 Hinged:
 Cam operated.
o Non-Contact Interlock:
o Motion Limits:
Mechanical Stops

 Physical stops that limit the travel of a robot’s joint.
 Can also be referred to as HARD Stops.
 Stops are usually adjustable.
Over Travel Limit Switches
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 Mechanical switches
 Usually positioned before the hard stops.
 Switches are optional.
 Wired directly to servo motor controls.
 Over travel can generate a JOG-001 violation warning.
Software Limits.
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 Established in system software.
 Set by system variables.
 Only usable after robot position is calibrated.
 Movement pass software limits will generate a JO-013 warning.
Cover robot safety zones 1-3.
Robot safety equipment and sensors.
- Robot E-stops
o Hardwired circuit that over rides all robot controls.
o Removes drive power from all actuators.
 Actuator: device that causes motion or movement.
o Applied dynamic braking to all robot driven joints.
 Dynamic Braking:
 Method used to stop a DC motor.
 Circuitry that uses stored energy in motor armature to produce a torque
opposite to motor direction which slows motor at a quicker rate.
o Teach pendant and SOP both have E-stop buttons.
- Deadman Switch
o Located on back of teach pendant.
o Two switches are present but only need to use one.
o Switch has three positions
 Release: Will not allow robot to jog
 Middle indent: Position required in order to jog robot.
 Fully depressed: Will stop movement of robot.
o Used when teach pendant is ON.
o With teach pendant in the ON position the servo power is disabled and robot brakes
are applied.
- Operator Safety
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Do not wear loose clothing
Remove watches and jewelry
Long hair not tied back or under a hat can be a safety hazard in a robot’s work cell.
Keep foreign items out of a work cell area.
Know your surroundings for a quick exit from the work cell.
Isolate robot from remote signals.
Know where all E-stop buttons are located.
Knowledge of robots work envelope.
- Robot Safety
o Always single step all new programs through one motion cycle at low speed..
o Run new program continuously though one cycle at a low speed.
o Run program through one cycle at production speed.
- Robot Movement
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Maximum Space: Robots full range of movement.
Restricted Space: Limiting devices that will stop the robot if activated.
Operating Space: Area that robot will move in order to complete its task.
Restricted and Operating spaces can be changed for different application.
Robot Controller
The standard operator panel is abbreviated SOP.
SOP is defined as the lights, push buttons, and key switch.
Two cabinets sizes:
Size A: Houses the SOP in a different panel than the controller.
Size B : SOP and controller in same ousing.
Key Switch
Auto Mode:
o Control from Teach pendant is disabled
o Used for production run at programmed speeds.
T1:
o Used to test programs using teach pendant.
o Joint speed is limited to 10% of full speed.
T2:
o Used to test programs using teach pendant.
o Full speed is enabled.