ROBOT SAFETY

• OBJECTIVES:

– BE ACQUAINTED WITH ROBOITIC SAFETY.– UNDERSTASND SFETY STANDARD.– RECOGNISE SAFETY RELIABILITY.– BE FAMILIAR WITH HUMAN FACTOR ISSUES.– BE AWARE OF SAFETY SENSORS AND MONITORING.– REALIZE SAFEGAURDING.– PERCEIVE THE IMPORTANT FACTORS OF TRAINING.– APPREHEND SAFETY GUIDELINES.– UNDERSTAND DEFINITIONS.

• SAFETY: METHOD AND TECHNIQUE USED FOR AVOIDING ACCIDENTS.

• INCLUDES THE USUAL CONSIDERATIONS OF MAN, MACHINE AND WORKSTATIONS, ENVIRONMENT, AND THE INTERDFACE BEHAVIOUR, BUT IT MUST ALSO CONSIDER SOFTWARE.

ROBOTS AND CONVENTIONAL MACHINERY• THREE MAJOR DIFFERENCES BETWEEN ROBOTS AND CONVENTIONAL

MACHINERY CAN BE IDENTIFIED THAT ARE CONCERN OF SAFETY PERSONNEL.– SPEED OF MOVEMENT.– PREDICTABILITY OF MOVEMENT.– HAZARD ZONES.

• IN CONVENTIONAL MACHINERY HAZARD ZONES MAY BE DIFFICULT TO RECOGNIZE, BUT ARE FIXED WITH TIME.

• ALSO THE MAIN DIFFERENCE BETWEEN CONVENTIONAL MACHINERY AND ROBOT IS THAT A ROBOT CAN BE :

– PROGRAMMED TO DO DIFFERENT JOBS.– REACT TO CHANGES IN THE PROCESS, EVEN MAKING DECISIONS FROM A

LIMITED NUMBER OF CHOICES.

• SAFETY ENGINEERING SHOULD BE APPLIED TO ROBOT SAFETY, PARTICULARLY IN THE HUMAN FACTORS ASPECTS AND SYSTEMS SAFETY APPROACHES.

• ROBOT SAFETY MUST INCLUDE THE USUAL CONSIDERATIONS OF MAN, MACHINE AND WORKSTATIONS, ENVIRONMENT, AND THE INTERFACE BEHAVIOR, BUT IT MUST ALSO CONSIDER SOFTWARE

CAUSES OF ACCIDENTS

• ENGINEERING DEFICIENCY• LACK OF PROPER PROCEDURES• INADEQUATE PROGRAMMING

• EMERGENCY STOP SWITCHES MUST APPEAR ON THE CONTROL PANEL AND ALSO BE ADDED TO THE PENDANT USED IN THE TEACH MODE WHERE THE OPERATOR OR PROGRAMMER MAY BE MOVING IN THE ROBOT’S WORK ENVELOPE.

• COMPREHENSIVE INSTRUCTION AND OPERATION PROCEDURES MUST ALSO BE INCORPORATED THROUGH TRAINING PROGRAMS.

SAFETY STANDARDS• SAFETY IS AN IMPORTANT CONSIDERATION IN INSTALLING,

PROGRAMMING, OPERATING, AND MAINTAINING ROBOT SYSTEMS.

• SAFETY CAN ALSO BE CONSIDERED AS A JUDGMENT OF THE ACCEPTABILITY OF DANGER, WHERE DANGER IS THE COMBINATION OF HAZARD AND RISK.

• HAZARD IS DEFINED AS INJURY PRODUCER, AND RISK IS DEFINED AS THE PROBABILITY THAT AN INJURY WILL OCCUR.

• THE CAUSES OF EMPLOYEE INJURY IN ROBOTIC ENVIRONMENT INCLUDES:

– PARTS OF THE BODY BEING CAUGHT.

– BEING STRUCK BY A PART OR ROBOT GRIPPER.

– FALLING FROM THE EQUIPMENT OR STRUCTURE.

– SLIPPING OR TRIPPING ON WALKING OR WORKING SURFACES.

– EXPOSURE TO DANGEROUS LEVELS OF HEAT OR ELECTRICITY

– EXCESSIVE PHYSICAL STRAIN

• SAFETY STANDARDS ARE VERY IMPORTANT IN THE WORKPLACE. ALL THE PROFESSIONAL ASSOCIATIONS HAVE DEFINED THE FOLLOWING PRIORITIES FOR ELIMINATING HAZARDS.

– ELIMINATE THE HAZARD THROUGH THE MACHINE DESIGN STAGE.

– APPLY SAFEGUARDING TECHNOLOGY.

– USE WARNING SIGNS AND LABELS.

– TRAIN AND INSTRUCT THE WORKER, PROGRAMMER, AND MAINTENANCE PERSONNEL.

– PRESCRIBE PERSONAL PROTECTIVE EQUIPMENT AND DEVICES.

HUMAN FACTOR ISSUES

• HUMAN FACTOR(ERGONOMICS) ISSUES OR ENGINEERING IS THE STUDY OF THE HUMAN-MACHINE INTERACTION AND IS DEFINED AS AN APPLIED SCIENCE THAT COORDINATES THE DESIGN OF DEVICES, SYSTEMS AND PHYSICAL WORKING CONDITIONS WITH THE CAPACITIES AND REQUIREMENTS OF THE WORKER.

• A MACHINE OR ROBOT SYSTEM DESIGNED WITH POOR ERGONOMICS WILL BE UNCOMFORTABLE AND TIRING TO USE, MAY EVEN BE DANGEROUS.

• BESIDES THE SIZE OF A ROBOT’S WORK ENVELOPE, ITS SPEED, ITS PROXIMITY TO HUMANS, AND INTERACTION WITH OTHER MACHINERY, MANY OTHER FACTORS SHOULD BE CONSIDERED AND INVESTIGATED SUCH AS:

– THE LAYOUT OF CONTROL PANELS.– TEACH-PENDANT ACCURACY.– PERSONNEL TRAINING– BARRIER GUARDS.– SAFETY DEVICES.– INTERLOCKS.– WARNINGS

• IN ADDITION HUMAN FACTOR ISSUES SHOULD INCLUDE EVALUATION OF A ROBOT WORKSTATIONS WHEN AN OPERATOR ENTERS THE WORKSTATIONS FOR MAINTENANCE, PROGRAMMING, AND THE LIKE.

SAFETY SENSORS AND MONITORING

• SAFETY MONITORING INVOLVES THE USE OF SENSORS TO INDICATE CONDITIONS OR EVENTS THAT ARE UNSAFE OR POTENTIALLY UNSAFE.

• THE OBJECTIVE OF SAFETY MONITORING INCLUDES NOT ONLY THE PROTECTION OF HUMANS WHO HAPPEN TO BE IN THE CELL, BUT ALSO THE PROTECTION OF THE EQUIPEMENT IN THE CELL.

• THE SENSORS USED IN THE SAFETY MONITORING RANGE FROM THE SIMPLE LIMIT SWITCHES TO SOPHISTICATED VISION SYSTEM THAT ARE ABLE TO SCAN THE WORKPLACE FOR INTRUDERS AND OTHER DEVIATIONS FROM THE NORMAL OPERATING CONDITIONS.

• GREAT CARE MUST BE TAKEN IN WORKCELL DESIGN TO ANTICIPATE ALL POSSIBLE MISHAPS THAT MIGHT OCCUR DURING THE OPERATION OF THE CELL, AND TO DESIGN SAFEGAURDS TO PREVENT OR LIMIT THE DAMAGE RESULTING FROM THESE MISHAPS.

LEVELS OF ROBOT SAFETY

• THE NATIONAL BUREAU OF STANDARDS DEFINES THREE LEVELS OF SAFETY SENSOR SYSTEMS IN ROBOTS.

– LEVEL 1 --- PERIMETER PENETRATION DETECTION.

– LEVEL 2 --- INTRUDER DETECTION INSIDE THE WORKCELL

– LEVEL 3 --- INTRUDER DETECTION IN THE IMMEDIATE VICINITY OF THE ROBOT.

• LEVEL 1 SYSTEMS ARE INTENDED TO DETECT THAT AN INTRUDER HAS CROSSED THE PERIMETER BOUNDARY OF THE WORKCELL WITHOUT REGARD TO THE LOCATION OF THE ROBOT.

• LEVEL 2 SYSTEMS ARE DESIGNED TO DETECT THE PRESENCE OF AN INTRUDER IN THE REGION BETWEEN THE WORKCELL BOUNDARY AND THE LIMIT OF THE ROBOT WORK VOLUME.

• LEVEL 3 SYSTEMS PROVIDE INTRUDER DETECTION INSIDE THE WORK VOLUME OF THE ROBOT.

• THERE ARE TWO COMMON MEANS OF IMPLEMENTING A ROBOT SAFETY SENSING SYSTEM

1. PRESSURE SENSITIVE FLOOR MATS --- ARE AREA PADS PLACED ON THE FLOOR AROUND THE WORKCELL THAT SENSE THE WEIGHT OF SOMEONE STANDING ON THE MAT. THESE CAN BE USED FOR EITHER LEVEL1 OR LEVEL2 SENSING SYSTEMS.

2. LIGHT CURTAIN --- CONSISTS OF LIGHT BEAMS AND PHOTSENSITIVE DEVICES PLACED AROUND THE WORKCELL THAT SENSE THE PRESENCE OF AN INTRUDER BY AN INTRRUPTION OF THE LIGHT BEAM. USE OF LIGHT CURTAINS WOULD BE MORE APPROPRIATE AS LEVEL1 SYSTEMS.

• PROXIMITY SENSORS LOCATED ON THE ROBOT ARM COULD BE UTILIZED AS LEVEL 3 SENSORS.

• THE SAFETY MONITORIN STRATEGIES THAT MIGHT BE FOLLOWED BY THE WORKCELL CONTROLLER WOULD INCLUDE THE FOLLOWING SCHEMES.

1. COMPLETE SHUTDOWN OF THE ROBOT UPON DETECTION OF AN INTRUDER.

2. ACTIVATION OF WARNING ALARMS.3. REDUCTION OF THE SPEED OF THE ROBOT TO SAFE LEVEL.4. DIRECTING THE ROBOT TO MOVE ITS ARM AWAY FROM THE

INTRUDER TO AVOID COLLISION.5. DIRECTING THE ROBOT TO PERFORM TASKS AWAY FROM THE

INTRUDER.

• NOTE: THERE IS ANOTHER SAFETY MONITORING CALLED A “FAIL-SAFE HAZARD DETECTOR.” THE CONCEPT OF THIS DETECTOR IS BASED ON THE RECOGNITION THAT SOME COMPONENT OF BASIC HAZARD SENSOR SYSTEM MIGHT FAIL AND THAT THIS FAILURE MIGHT NOT BE FOUND OUT UNTIL SOME SAFETY EMERGENCY OCCURRED. THE FAIL-SAFE HAZARD DETECTOR IS DESIGNED TO OVERCOME THIS PROBLEM.

SAFEGUARDING

• MOST INDUSTRAIL ACCIDENTS OCCUR ARE THE RESULTS OF UNSAFE ACTS BY THE WORKER. UCH ACTS CAN OCCUR DUE TO:

– IMPROPERLY TRAINED OPERATORS.– CARELESS PROGRAMMERS ACTIVATING THE WRONG CONTROLS.– COMPONENT FAILURE OR OTHER UNSAFE CONDITIONS IN THE

PLANT.

• MAJOR CONCERN IN SAFETY OF ALL PERSONNEL INVOLVED WITH INDUSTRIAL ROBOTS IS VERY IMPORTANT.

• ACCORDING TO THE NATIONAL SAFETY COUNCIL(1991) THE PRINCIPAL HAZARDS ASSOCIATED WITH ROBOTS ARE AS FOLLOWS:

1. BEING STRUCK BY A MOVING ROBOT WHILE INSIDE THE WORK ENVELOPE.

2. BEING TRAPPED BETWEEN A MOVING PART OF A ROBOT AND ANOTHER MACHINE, OBJECT, OR SURFACE.

3. BEING STRUCK BY A WORKPIECE, TOOL, OR OTHER OBJECT DROPPED OR EJJECTED BY A ROBOT.

SAFEGUARDING (CONTD.)

• ROBOT SAFEGUARD:

– TO ERECT A PHYSICAL BARRIER AROUND THE ENTIRE PERIMETER OF A ROBOT’S WORK ENVELOPE.

– A GUARD CONTAINING A SENSING DEVICE THAT AUTOMATICALLY SHUTS DOWN THE ROBOT IF ANY PERSON OR OBJECT ENTERS ITS WORK ENVELOPE CAN BE EFFECTIVE.

– TO PUT SENSITIZED DOORS OR GATES IN THE PERIMETER BARRIER THAT AUTOMATICALLY SHUT DOWN THE ROBOT’S MOVEMENT WHEN THEY ARE OPENED.

• SAFEGUARDING (CONTD.)

• EVEN THOUGH IT IS DIFFICULT TO GO TO A RISK-FREE ENVIRONMENT BECAUSE THER IS ALWAYS THE POSSIBILITY OF A MALFUNCTION OR THE VIOLATION OF GOOD SAFETY PRACTICES. HOWEVER, THERE ARE WAYS TO MINIMIZE THE POTENTIAL OF THESE ERRORS:

1. SAFETY TRAINING2. DEPENDABLE MACHINE DESIGN3. HIGH-RELIABILITY CONTROLS4. PROPER LAYOUT WORK AREA.5. SAFE POSITION AND CLEAR VISIBILITY FOR

PROGRAMMING.6. ESTABILISHING PROPER MAINTENANCE PROCEDURES.7. ADEQUATE INSTALLATION PERFORMED IN THE

PRESENCE OF SAFETY PERSONNEL.8. OBEYING SAFETY RULES AND REGULATIONS OF

AUTHORITATIVE ORGANIZATIONS.

SAFETY GUIDLINES

• THE UNEXPECTED ROBOT MOVEMENTS ARE THE CONCERN OF EMPLOYEES FOR OBTAINING FURTHER GUIDELINES ON ROBOTICS SAFETY.

• RESEARCHERS HAVE DEVELOPED MANY GUIDELINES PERTAINING TO SAFETY ISSUES IN ROBOTS.

• FOLLOWING GUIDELINES ARE FOR SAFE USE OF ROBOTS IN A PRODUCTION ENVIRONMENT:

1. IF THE ROBOT IS NOT MOVING, DO NOT ASSUME IT IS NOT GOING TO MOVE.

2. IF THE ROBOT IS REPEATING PATTERN, DO NOT ASSUME IT WILL CONTINUE.

3. ALWAYS BE AWARE OF WHERE YOU ARE IN RELATIONSHIP TO THE POSSIBLE POSITIONS THAT THE ROBOT MAY REACH.

SAFETY GUIDELINES (CONTD.)

4. BE AWARE IF THERE IS POWER ACTUATORS. INDICATOR LIGHTS WILL BE ON WHEN THERE IS POWER TO THE ACTUATORS.

5. TEACHING, PROGRAMMING, SERVICING, AND MAINTENANCE ARE THE ONLY AUTHORIZED REASONS FOR ENTRY INTO THE WORK ENVELOPE.

6. BEFORE ACTIVATING POWER TO THE ROBOT, EMPLOYEES SHOULD BE AWARE OF WHAT IT IS PROGRAMMED TO DO, THAT ALL SAFEGUARDS ARE IN PLACE, AND THAT NO FOREIGN MATERIALS ARE PRESENT WITHING THE WORK ENVELOPE.

7. NOTIFY SUPERVISION IMMEDIATELY WHEN AN UNEXPECTED INTERRUPTION TO THE NORMAL ROBOT WORK CYCLE OCCURS.

8. REPORT ANY MISSING OF DEFECTIVE SAFEGUARD TO SUPERVISION IMMEDIATELY. CHECK ALL SAFEGUARDS AT THE BEGINNING OT EACH SHIFT.

SUMMARY• SAFETY IS AN IMPORTANT COMPONENT IN INDUSTRIAL

AUTOMATION.

• ROBOT SAFETY DEPENDS ON THE SIZE OF THE ROBOT’S WORK ENVELOPE, ITS SPEED, AND ITS PROXIMITY TO HUMANS.

• SAFETY SENSORS AND MONITORING PROVIDE THE CAPABILITY OF THE WORKCELL CONTROLLER AND ITS SENSORS TO MONITOR THE OPERATION DURING UNSAFE CONDITIONS IN THE CELL.

• SAFEGUARDING IS THE PREVENTION OF INJURY OR ACCIDENT IN THE WORKPLACE.

• TRAINING IS A MAJOR FACTOR IN THE SUCCESSFUL IMPLEMENTATION OF ANY ADVANCED TECHNOLOGY IN A COMPANY OR OPERATION.

• SAFETY GUIDELINES HAVE BEEN DEVELOPED BY RESEARCHERS PERTAINING TO SAFETY ISSUES IN ROBOTS TO REDUCE OR ELIMINATE ACCIDENTS IN A PRODUCTION ENVIRONMENT.