72341840.pdf

International Journal of Production Research Vol 50 No 1 1 January 2012 161 176 Impact of dynamic virtual and real robots on perceived safe waiting time and maximum reach of robot arms Parry P W Nga Vincent G Duffybcd and Gulcin Yucelbe aSchool of Industrial Engineering and Engineering Management The Hong Kong University of Science and Technology Clear Water Bay Kowloon Hong Kong SAR China bSchool of Industrial Engineering Purdue University West Lafayette Indiana USA cRegenstrief Center for Healthcare Engineering Purdue University West Lafayette Indiana USA dSchool of Agricultural and Biological Engineering Purdue University West Lafayette Indiana USA eSchool of Industrial Engineering Istanbul Technical University Istanbul Turkey Final version received February 2011 This research examines perception of dynamic objects and robots in a virtual and real industrial work environment The studies are modelled after those of Karwowski and Rahimi from the early 1990s By applying virtual reality technology the real workplace can be simulated in the virtual world for the improvement of facility design Perception of hazard and risk safe waiting time maximum reach of robot arm are measured related to the impact of parameters such as robot size speed and type and exposure to a virtual accident Analysis includes techniques such as sequential experiments to compare results in the virtual and real environments These methods may be considered as a model for studying perception and transfer in other domains The comparison of the analysed data in the virtual and real environments helps to further determine the transferability of performance and perception from virtual reality to real Results show similarity in perceived safe waiting time but there are large differences in perceived maximum reach of robot arms between the virtual and real environments Using the preliminary results from the integrated data in the sequential experiments potential guidelines for using virtual facility layout in industry are discussed Keywords human robot interaction perception of hazard and risk maximum reach of robot arms sequential experiment data bridging 1 Introduction Many industrial companies utilise industrial robots to perform dangerous tasks in industry to avoid possible hazards Still others are attempting to reduce musculoskeletal disorders through the use of hybrid automation such as assist devices Nussbaum 2000 According to the World Robotics 2007 published by Union Nations Economic Commission from Europe www euron org there were approximately 951 000 units in 2006 and it is expected to be 1 200 000 units in 2010 Table 1 Since the robots are used more frequently in workplaces issues related to human robot interaction HRI are more often considered by researchers and practitioners According to Dhillon et al s 2002 survey 523 papers about robot safety and reliability were published between 1973 and 2000 Most of this research was done between 1982 and 1990 and robot safety and reliability research has been incrementally decreased since 1986 Dhillon et al 2002 On the other hand between 1995 and 2000 multidisciplinary research in HRI has been more recently started by the collaboration of researchers from human factors robotics cognitive science psychology and natural language and during that time many conferences and workshops were dedicated to HRI such as IEEE International Symposium on Robot and Human Interactive Communication RoMan Association for the Advancement of Artificial Intelligence s AAAI Symposia Series IEEE International Conference on Robotics and Automation ICRA Goodrich 2007 Since 2006 international HRI conference has been held annually One of the issues related to HRI is the safety of the users In reference to the statistics on Occupational Injuries compiled by the Labour Department of Hong Kong Government in 2007 there were 3967 injuries and 21 fatalities in the manufacturing industry in total They indicated that there had been 491 workers injured due to striking against or being struck by dynamic moving objects the number one type of accident in the manufacturing industry Hong Kong Labour Department 2007 Previous research on robot safety has been done along two separate Corresponding author Email duffy purdue edu ISSN 0020 7543 print ISSN 1366 588X online 2012 Taylor one included experiments both with simulated and physical robots Because of cost and reliability concerns most of the time it is not possible to conduct experiments with real robots On the other hand in simulation experiments the real world s detail situations cannot be represented very well Therefore in this study the experiments were done both in real and virtual environments Analytical results are compared in the dynamic virtual and real environments with moving hazard using the Table 1 Summary of number of robots working in industry worldwide Number of robots Working in industry worldwide951 000 Projected to be working by 20101 200 000 Per 10 000 manufacturing employees in Japan349 Per 10 000 manufacturing employees in Republic of Korea187 Per 10 000 manufacturing employees in Germany186 Per 10 000 manufacturing employees in the United States99 Source World Robotics 2007 United Nations Economic Commission for Europe 162P P W Ng et al sequential experimental techniques Snow and Williges 1998 Based upon the results obtained from the experiment the transferability of the experience perception from virtual to real worlds and similarities and differences of the results given by Karwowski Karwowski et al 1988a 1988b Karwowski and Pongpatanasuegsa 1990 Rahimi and Karwowski 1990 Karwowski and Rahimi 1991 and this research can be shown 1 1 Safe robot speed The causes of accidents related to robots could be ascribed to some human perceptual physical and psychological limitations including human perception of robot size speed and range of motion that can affect the human behaviour Carlsson 1984 Different speed of robots can cause different perceptions of hazards Kulic and Croft 2006 and Ikuta et al 2003 used velocity as an input while developing a danger index during HRI The force exerted by robot arms is high with fast speed of robot motion However it should be noted that Haddadin et al 2007 conducted crash tests with robot and dummy head to decide the impacts of collisions between robot and human They reported that a robot with arbitrary mass driving moving at speeds up to 2m s cannot be dangerous to a non clamped head with respect to the severity indices used in the automobile industry that are based on head acceleration It can also be noted that other research reported that the human was not in danger for impact with the human chest abdomen and shoulder at robot velocities up to 2 7m s Beside robot velocity robot mass s affect on head injury criterion HIC was also investigated and it was reported that a heavy robot cannot pose a significant threat to the human head by means of HIC Haddadin et al 2008 2009 Even though the safe robot operating conditions such as speed under 2 7m s mechanical output under 150N etc remove physical risks HRI still involves risks related to the mental strains caused by robot motion Aria et al 2010 It should be emphasised that this study is focused on cognitive aspects of robot safety In this study robot speeds are chosen 25 and 90cm s for experiments above and below the thresholds of concern since it was previously shown that people feel threatened by robot speed above 64cm s Karwowski and Rahimi 1991 Aria et al 2010 studied mental strains of a human operator in a cell production system where an operator assembles a product with the aid of parts feeding by the robot Based on their physiological assessment and subjective assessment results the operator feels discomfort when the robot s speed is more than 500mm s It can also be mentioned that the initial impact may not be the greatest reason for the concern expressed by the operators Especially with large robots operators are aware that the potential for a pin of body parts against other objects after impact is highly likely if a collision occurs since the robot does not necessarily stop after impact whereas in an auto and in transportation there is nothing to continue to drive the collided objects together after initial impact Hence operators perception of their own reaction time may be influencing their perceived safe robot speed rather than simply a concern over the damage at initial impact 1 2 Perception of safe robot idle time The American National Safety Standard American National Standards Institute 1986 ANSI R15 06 was established for robot safety in the United States Also the Occupational Safety and Health Administration OSHA in the US provided guidelines for robot safety OSHA 1987 The standards related to robotic safety are summarised in Table 2 According to Bonney and Yong 1985 and Nagamachi 1986 1988 the complex robot systems are potentially hazardous even in the normal mode of operation Most accidents happened because robot operators misperceive the reasons for pauses which are either system malfunctions or programmed stops Sugimoto and Kawaguchi 1983 Accident reports have shown that people can be injured or be killed by robot arms if they misperceive the work envelope and enter it during the robot operation 1 3 Simulated accident A simulated accident can be introduced to influence the behaviour since the expected shift in the processing of information brings the task into the cognitive realm Lehto and Papastavrou 1993 Park 1997 Rahimi and Karwoski 1990 suggested that the idle times must be considered in designing the facility layout and robot programmes It is expected that the exposure to a simulated accident will influence the waiting time to enter the International Journal of Production Research163 work envelope for both robots As suggested by Parsons 1986 1987 it has been shown that the simulated robot accidents influence the robot operator after training Karwowski et al 1991 Hypothesis 1 It is expected that factors of exposure to a simulated accident size speed and type of robots will affect waiting times i e idle times significantly in both the virtual and real environments 1 4 Perception of maximum reach of robot arms The robot work envelope is defined as the maximum reach of robot arms or the unsafe zone of a robot According to Karwowski 1991 the maximum reach of robot arms were significantly affected by factors such as accident exposure size speeds and type of robots The methodology from Rahimi and Karwowski 1990 and Karwowski et al 1991 are replicated in this study and the results will be compared Wright 1995 reported that real world distance perceptions are usually 87 90 of actual distances Lampton et al 1995 showed the tendency for underestimating distance in both the virtual and real environments but the distance in virtual were more extremely underestimated than that in real Witmer and Kline 1998 attempted to determine how accurately stationary observers could estimate distances to objects i e cylinders in a simple virtual environment given by static cues for distance and defined perceived distance judgement by referring to tasks in which stationary observers judge the distance between themselves and a stationary or moving object immediately perceivable to them Based on the results from Witmer and Kline 1998 people generally underestimated distance to the objects in the virtual and real environments but the errors in distance estimation was to be greater in virtual than that in real Moreover they showed that the size of the object i e cylinders influenced the estimated distance significantly but floor texture and pattern did not Hypothesis 2 Perception of the work envelope of the robot is related to exposure to a simulated accident speed types and sizes of robots in both the virtual and real industrial work environments 1 5 Sequential experimentation and data bridging A sequential experimentation research strategy was proposed by Williges and Williges 1989 which could be utilised for human factors studies to investigate and examine a large number of independent variables using a series of small sequential studies The results from the sequential studies can be integrated to build the empirical models to explore the effects of different independent variables and predict human performance Han 1991 Table 2 Robot safety standards ANSI RIA R15 06 199 The American National Safety Standard Robot safety Includes risk assessment methodology and guidelines for safeguarding robotic system CSA 2434 2003Canadian Standards AssociationSimilar to US standards by minor differences ISO 12100International Standard Office Safety of Machinery Standard Basic concepts general principles for design ISO 10218International Standard Office Robots for industrial environments safety requirements Requirements and guidelines for the inherent safe design protective measures and infor mation for use of industrial robots IEC61508Functional safety of electrical electronic programmable E E PE electronic safety related systems Requirements to minimise dangerous failures in E E PE safety related systems OSHAOccupational Safety and Health Administration An interpretation of ANSI standards and a directive concerning of robotics safety Source Spada 2005 164P P W Ng et al Data bridging can be treated as a statistical method for integrating results across sequential studies Han 1991 If there are no significant differences in the responses from the common data points the data can be considered as from the same experiment and combined into a common data set in order to build the model Snow and Williges 1998 Based on these results it is believed that a comparison of virtual and real experiments could be allowed if the data could be merged into a common data set based on the use of data bridging in the virtual experimental conditions 2 Methods 2 1 Subjects for robot experiment Sixty four 32 males and 32 females engineering students were recruited from the Hong Kong University of Science and Technology HKUST The subjects of the experiment had a basic understanding about robot programming and operations The experiments took about 2h Each participant was paid 200 Hong Kong dollars 7 8HKD 1USD for their participation All participants were divided into eight groups with eight participants in each group 2 2 Equipments robot experiment Two industrial robots Yaskawa MOTOMAN K10S and SONY SRX 410 were investigated in this research Both robots are located in the CAD CAM laboratory of the Hong Kong University of Science and Technology Yaskawa MOTOMAN K10S is a vertically articulated robot with six degrees of freedom and is mounted on the floor Its controller is a servo drive controlling system The payload capacity of the robot is 10kg The position repeatability of the robot is 0 1mm The base rotation of the robot is 320 degrees about the base The maximum reach of robot arm of MOTOMAN K10S is 1555mm and the combined linear speed of all axes is 1500mm s Its position repeatability is 0 1mm The SONY SRX 410 is a SCARA type high speed assembly robot It is a compact desktop design with four axes DC servo motor control The work envelope of the robot is 600mm first arm 350mm second arm 250mm The maximum speed of linear motion first and second arms combined is 5200mm s The weight of the robot is 60kg 132 2lbs Its payload capacities are 5kg at low speed 3kg at medium speed and 2kg at high speed The position repeatability of robot for the X Y axis and Z axis are 0 025mm and 0 02mm respectively Figures 1 and 2 show the Yaskawa MOTOMAN K10S and SONY SRX 410 robot respectively The real workplace with two robots is simulated in the dynamic virtual world by using the Virtual Reality Modeling Language VRML A Pentium III 600MHz computer with a Sony 1700Video Display Terminal VDT monitor V frequency 75Hz H frequency 60kHz was used and Java Script provided animation in the VRML environment In the VRML environment the robot motion was controlled start and stop through the program buttons of control panels using an Internet Explorer browser with Cosmo player plug in Since the VRML program is a virtual internet based system the computer is needed to connect the network to the Internet World Wide Web WWW Figures 3 and 4 show the MOTOMAN K10S and Sony SRX 410 robots in the virtual environment respectively 2 3 Experimental design In this study the four experiments can be divided into two main categories 1 idle time experiment and 2 maximum reach of robot arm experiment Each category of the experiment had two parts one was the virtual part and the other one was the real part All participants belonging to the real group were required to perform some virtual trials to fulfil the requirement of data bridging for the sequential experiment in order to do the common point testing For the real group half of the subjects 16 subjects performed tasks in the real environment first and the other half performed some tasks in the virtual environment first A simulated accident was shown to half of the subjects 16 subjects in the real group and 16 subjects in the virtual group International Journal of Production Research165 2 3 1 Idle time experiment This experiment was a six factor ANOVA mixed design 2 genders 2 accident exposures 2 speeds 2 sizes 2 types of robots 2 lighting levels All independent variables had two levels The between subject variables are gender males or females and accident exposure Yes or No The other four within subject independent variables are speed of the robot 10cm s or 90cm s size of the robot large or small types of robots Sony SRX 410 or Yasakawa MOTOMAN K10S and lighting condition bright or dark The dependent variable perceived idle Figure 1 Yaskawa MOTOMAN K10S Figure 2 Sony SRX 410 Figure 3 Virtual Yaskawa MOTOMAN K10S Figure 4 Virtual Sony SRX 410 166P P W Ng et al time of robot is the time that the subjects wait as long as they feel that it is safe for them to enter the wor