机械类英文参考文献

Int J Interact Des Manuf(2011)5:103–117DOI10.1007/s12008-011-0119-7ORIGINAL PAPERBenchmarking of virtual reality performance in mechanics educationMaura Mengoni·Michele Germani·Margherita PeruzziniReceived:27April2011/Accepted:29April2011/Published online:27May2011©Springer-Verlag2011Abstract The paper explores the potentialities of virtual reality(VR)to improve the learning process of mechanical product design.It is focused on the definition of a proper experimental VR-based set-up whose performance matches mechanical design learning purposes,such as assemblability and tolerances prescription.The method consists of two main activities:VR technologies benchmarking based on sensory feedback and evaluation of how VR tools impact on learning curves.In order to quantify the performance of the technol-ogy,an experimental protocol is defined and an testing plan is set.Evaluation parameters are divided into performance and usability metrics to distinguish between the cognitive and technical aspects of the learning process.The experi-mental VR-based set up is tested on students in mechanical engineering through the application of the protocol. Keywords Mechanical product design·Virtual reality·Experimental protocol·Learning curve·Mechanics education1IntroductionModern society is dominated by continuous scientific and technical developments.Specialization has become one of the most important enablers for industrial improvement.As a result,nowadays education is more and more job-oriented and technical education is assuming greater importance.In this context both university and industry are collaborating to create high professional competencies.Thefirst disseminates M.Mengoni(B)·M.Germani·M.PeruzziniDepartment of Mechanical Engineering,Polytechnic University of Marche,Via Brecce Bianche,60131Ancona,Italye-mail:m.mengoni@univpm.it knowledge and innovative methods while the second pro-vides a practical background for general principles training. The main problem deals with the effort and time required to improve technical learning,while market competitiveness forces companies to demand young and high-qualified engi-neers in short time.Therefore,the entire educational process needs to be fast and efficient.Novel information technolo-gies(IT)and emerging virtual reality(VR)systems provide a possible answer to the above-mentioned questions.Some of the most important issues,in mechanical designfield,are the investigation of such technologies potentialities and the evaluation of achievable benefits in terms of product design learning effectiveness and quality.While IT has been deeply explored in distance education,i.e.e-learning,VR still rep-resents a novelty.VR refers to an immersive environment that allows pow-erful visualization and direct manipulation of virtual objects. It is widely used for several engineering applications as it provides novel human computer interfaces to interact with digital mock-ups.The close connection between industry and education represents the starting point of this research. Instead of traditional teaching methods,virtual technolo-gies can simultaneously stimulate the senses of vision by providing stereoscopic imaging views and complex spatial effects,of touch,hearing and motion by respectively adopt-ing haptic,sound and motion devices.These can improve the learning process in respect with traditional teaching meth-ods and tools.The observation of students interpreting two-dimensional drawings highlighted several difficulties:the impact evaluation of geometric and dimensional tolerances chains,the detection of functional and assembly errors,the recognition of right design solutions and the choice of the proper manufacturing operations.These limitations force tutors to seek for innovative technologies able to improve students’perception.Investigations into the use of VR have indicated that it may improve the learning process offering a more useful product’s representation and creating an augmented environment for the models investigation and description.The main problem deals with the effective application of a VR system into edu-cational situations and the appraisal of its impact on learning. These are crucial points if we consider that the definition of a proper VR arrangement for specific lesson purposes has to be correlated to the learning process as the result of indi-vidual skills(procedural aspects)and instrumental practice (declarative aspects).The scope of this research is the experimentation of VR in mechanical product design teaching,the assessment of the limits and advantages of available technologies and,finally, the evaluation of the achieved learning process performance.In this context,the paper aims at defining both a proper VR set-up for mechanical product design teaching and an exper-imental protocol for validation tests.A method is proposed to benchmark current VR technologies.It is based on the study of product design lessons by traditional means of rep-resentation,on the identification of the main critical activities where paper-based tools and CAD systems usually fail and on the correlation between the identified activities and tools usability,achieved presence and depth of sensations that are perceived into the experienced-based learning environment. Then an experimental protocol based on specific context met-rics is defined.It aims at evaluating both the learning process performance for the specific purpose and the usability of the adopted VR-based set-up.2Background:VR technologies for learning purposes2.1Learning environments for mechanical product designA learning environment is characterized by active interac-tions among all involved individuals.Kaye[13]in particular states that learning is an individual process but it is always influenced and stimulated by the external context.Only by conversation and comparison with peers and experts,stu-dents reach a solid knowledge of the specific topics.Mul-tidisciplinary environments are particularly appropriate for educational purposes:scientific studies showed that human learning usually happens for83%by sight,only10%by hearing and the rest by other senses[17].On the other hand, collaborative environments provide learners with several advantages such as the opportunity to experience the multi-ple standpoints of other learners with different backgrounds and the ability to develop critical thinking skills through the process of judging and valuing.In order to improve col-laboration,advanced digital technologies may help students for incrementing learning by simulating real design process operations and by sharing the design outcomes[10].A recent study shows that design education can be implemented by two main different approaches[22]:•face-to-face education,that improves the learners-learners and learners-instructors interaction.The main problems in experience-based learning application are related to retrieving information,developing collaborative work and experiencing design solutions in real time;•distance education,that implies learners and instruc-tors in geographically separated sites.Three different approaches and related communication media are pro-posed:(a)one-way instruction by mail,radio and televi-sion,(b)single technology instruction by computer-based or web-based learning,and(c)blended learning that com-bines face-to-face with asynchronous and/or synchronous computer technology.The same study demonstrates that face-to-face is more suc-cessful than distance learning in mechanical product design where the understanding of design topics requires a concrete experimentation of general principles.The concept of expe-rienced-based learning has been widely explored in design teaching.It basically consists of the following steps:con-crete experience of technical problems and solutions,obser-vation of the achieved results and formulation of abstract concepts and generalizations[14].Other researches claimed that learning without execution of action remains at the state of mental action and therefore distant from real action[21]. These preliminary considerations point out the importance of adopting educational methods and tools that make students experience design topics in an effective way.A suitable learn-ing set-up ought to answer students’needs and to enable them to reach educational goals.2.2Potentialities of VR in mechanical product designteachingTraditional teaching is almost entirely centred on2D rep-resentations that make difficult the interpretation of differ-ent design solutions and errors detection.Nowadays CAD systems offer3D models visualization and animation that support assembly comprehension by a better visual charac-terization.Otherwise perception is still limited only to sight and it does not significantly increment the learning process. It is worth to notice that CAD systems functionalities are not able to support the identification of awkward reach angles or relevant assembly/disassembly issues.The use of experimental laboratories may overcome the above-mentioned problems.They allow students to experi-ence mechanical equipments and manufacturing operations. High costs of maintenance,great initial investments and the increasing number of classroom students make laboratories not easy to be kept up.VR-based environments seem to be a valid solution to improve mechanical design topics learning.However this intuitive assumption needs to be objectively demonstrated. Researches into the use of VR have indicated that it may offer more useful artefacts representations and simulate the relevant characteristics of a product such as engineering, manufacturing and maintenance aspects[6].In particular,in assembly and tolerances analysis VR environments can sup-port realistic interaction between parts by real-time simula-tion of physical constraints and an intuitive interface,which allows natural manipulation.Some studies have suggested also that adding force feedback to assembly,virtual anal-ysis increases task efficiency and performance[1,25]while eliminating physical prototypes gives substantial cost savings [23].Finally,virtual environments may easily create collabo-rative spaces where students learn multiple-level information about the product,listen to different interpretations and share their learning experience to develop their own practical and cognitive skills.Most of the recent studies on face-to-face design education highlight the potentialities of VR technologies to improve perception in education and training applications[4,20,24].The main advantages recognized to VR applications are:•the improvement of the spatial ability of learners as they allow not only the visualization of3D models but also their experimentation.Furthermore studentsfind them much easier to understand things from diagrams or mod-els simply looking at graphs or mathematical algorithms;•the knowledge sharing facilitation and the collaboration in multidisciplinary teamwork;•the achievement of sense of presence instead of traditional visualization technologies;•the interaction with virtual models in a very intuitive and natural manner.Although the above-mentioned advantages,no experimen-tal results have been achieved in selecting the most suitable technologies for mechanics education tasks.This is mainly due to the high costs of VR technology implementation,the difficulty to identify the proper VR technologies combina-tion for the specific learning purposes and the complexity to understand how it impacts on the learning curve.2.3Evaluation of VR technologies in the learning process The ability of a mechanical designer is earned by experience and practice and could be considered the outcome of his/her learning process.Over the years,several models were devel-oped to capture the human performance in carrying out a task. They are usually based on two main learning curves forms: time-based or performance-based representations.Outlining learning curve has become a very popular method thanks to its simplicity of use and its ability tofit empirical data well [15].From the learning point of view,mechanical product design implies a sequence of mental and practical activi-ties,such as the creation of solid models,their assembly, the comprehension of their interrelations and their particular functions.The transfer of acquired expertise depends on both the individual aptitude for learning and traducing action into experience(cognitive level)and the support and ease to use of tools(technical level).Considering the case under inves-tigation,the thinking processes allow students to elaborate the right procedure for product design,but the mere course of actions does not lead to a successful result.Furthermore, tools’usability and learnability influence the learning pro-cess.Several studies stressed the need to understand how new technologies affect learning curves in order to establish the appropriate training and assessment[8].Recent works are notably oriented to considerfinal learning as the sum of cog-nitive and technical components.Hamade et al.[7]develop a method to assess the speed and proficiency of CAD sys-tems learning,based on test exercises and on the measure of two objective factors,performance time and feature count. The study interest lies not only in the objectivity and porta-bility to other contexts,but also in the distinction between procedural and declarative knowledge.Total learning curve is set up and decomposed into its cognitive and behavioural components through a dual-phase learning model approach. However the method leaves out the usability of equipment and it uses only objective metrics underestimating the sub-jective components.Distinction of cognitive and technical aspects is cited also by Blavier et al.[3].They achieve a more complete evalu-ation and include the perceptual and the technology impact on the learning performance.The research estimates learning curves in a comparative study between classical and robotic laparoscopy and appeals both to objective data collected dur-ing experimental tests and subjective data collected by ques-tionnaires.Both objective and subjective data are required for an accurate evaluation of a VR-based set-up for mechanical learning purpose.This is the focus of the present research. This way allows measuring performance advantages and establishing how much the VR system contributes to stu-dents’learning experience.3The VR-based set-up for mechanical product design learning3.1VR technologies classification based on perception Perception in design education plays a crucial role in incrementing knowledge.Although several researchers areconcentrated on visual perception[18],it is worth to notice that individuals perceive objects and the space surrounding them also by all other sensorial modalities.Human beings depend onfive senses to experience their surroundings and infer from the physical objects and envi-ronment around ers interact with objects and their interface by experiencing them with their sensorial modali-ties that generate a set of stimuli.They arefirst elaborated at a cognitive level and then transformed into actions.In order to obtain similar conditions by VR,it is necessary to identify which technology better stimulates each sense and provides deep sensations in the users.The proposed classification starts from the Burdea’s def-inition of VR as“a high-end user-computer interface that involves real time simulation and interactions through mul-tiple sensorial channels”[2].Available VR technologies are divided into four classes(visual,sound,haptic and motion) that correspond to the four sensorial channels involved in the virtual experience(vision,hear,touch and motion).Each of them provides the corresponding sensorial feedback to the users(Fig.1).The sense of motion,sometimes called the sixth human sense,is usually achieved via some means of position and orientation tracking that mediate the user’s input into the VR simulation.They include all navigation and manipulation technologies.The sense of touch is performed by what are called haptic technologies.Tactile and force feedback devices seek to simulate tactile cues.The sense of vision is provided by visualization technologies.They can be divided into sin-gle-user displays and multi-users displays.Thefirsts are gen-erally desk-supported while the seconds are large volume displays that allow the simultaneous collaboration of several individuals.They can beflat or curved,front of rear projec-tion-based;they may provide passive or active stereoscopic experience.The sense of hearing is provided by sound tech-nologies:stereo sound,specializing multiple sound sources and3D sound.They differ from each other in the level of realistic feedback they supply to the user.In order to achieve a fully immersive environment that improves students’perception of the virtual scene,also smell and taste feedback must be simulated but the complexity of these senses has made them difficult for available VR tech-nology to conquer.All these technologies are also combined with the com-puting hardware for VR real-time simulation and interaction support and with the software toolkits to map the input/output devices with the digital scene,model3D objects and create libraries for optimising VR simulations.Fig.1The proposedclassification of VR technologies and the correlation with the humansenses3.2A method for VR benchmarking to achieve the learninggoalsIn order to improve experimental-based learning by VR tech-nologies,students should feel being involved in the virtual environment and be allowed to test principles by touching, hearing and moving the objects they are working with.It has been demonstrated that the communication medium influ-ences the form of interaction and knowledge perception and cognition,particularly when learners are unfamiliar with the communication technologies used to deliver instruction and perform design tasks[19].Therefore we state that in VR applications for education,it is important to evaluate not only the level of involvement perceived by the user but also the system’s usability.Based on these considerations,the benchmarking of VR technologies combination is based on three different clas-ses of heuristics:usability,presence and depth of sensations. Usability concerns the capacity of the VR interfaces to meet the users’needs.The degree of the system usability depends on different characteristics such as the adopted tools bar-rier free,ease-to-use,intuitiveness.Presence means“being immersed”and refers to an emotional and mental state of being involved in the virtual scene;it denotes the level of engagement.The sense of presence is determined by some characteristics of the system such as interactivity,collabo-ration,non constraining or navigation support.Finally,the depth of sensation refers to the degree of the sensory feed-back(visual,tactile,auditory)that users feel while exploring the virtual space.In order to manage the complexity of all possible combi-nations of VR technologies,a matrix-based method is intro-duced.Two3D matrices are used to connect technologies and human senses:thefirst allows the management of the combination between haptic,visual and navigation technol-ogies,while the latter matches thefirst achieved arrange-ment with sound technologies and assigns a value for each final combination to each heuristics for assessing the system’s performance(Fig.2).In order to identify which VR combina-tion is suited to teach specific mechanical design subjects we introduce an additional matrix,which correlates the activ-ities necessary to perform experienced-based learning and the levels of sensory feedback necessary for perception and cognition.On the contrary of previous matrices,that are ful-filled by VR experts as they relate to technical and functional performances and are not design learning-oriented,this addi-tional matrix needs to be fulfilled by professors of mechanical product design for their deep experience of learning environ-ments.The method application preliminarily requires the analy-sis of which activities should be performed to gain a good understanding of the lesson subjects.In the study context, two different mechanical product design topics have been explored and for each of them the necessary teaching activi-ties have been traced.•Product functional design and assembly principles.The topic aims to develop a critical attitude in the interpretation of mechanical components and assemblies,in functional errors detection and in the identification of assembly problems.In functional design the tutor generally shows different functional alternatives in order to clarify these concepts.The use of examples is considered fundamental to improve general principles understanding.•Dimensional and geometric tolerances.The topic aims to develop the ability of identifying assembly and manufacturing problems in different design solutions and the relation between tolerances andfinal product quality.In particular students should be able to ver-ify the consequences of tolerances prescription onthe Fig.2Synthesis of the proposed methodTable 1Assessment of the sensory feedback necessary to undertake the necessary activities for learning product functional and assembly principles and geometric and dimensional tolerances prescriptionValuationLevels of sensory feedback Definition of the levels of sensory feedback for teaching purposes Sense of sight Sense of touch Sense of hearing Sense of motionAssessment of design solution alternatives combining different standard components with similar functions5513Assessment of the impact of design decisions on manufacturing and assembly operations5353Identification of manufacturing and assembly problems by analyzing manufacturing operations and equipments 251Identification of the rightfunctional design solution by analyzing the manufacturing and assembly cycle costs of different alternatives3411Detection of functional and assembly errors in different design solutions5555Understanding components interaction in assemblies and identification of the proper sequence of assembly operations 3555Absolute Importance ( bij)61Relative Importance (ai*bij)253Requested value of sensory feedback ( ai*bij/ 5*bij)0.87Interpretation of a design solution and identification of the tolerances352Identification of the dimensional and geometric tolerancesreferences and of the difference between them3524Understanding of the differences between tolerances according to the control techniques433Identification of the manufacturing and assembly problems deriving from wrong tolerances chain 5513Assessment of the impact oftolerances chain on the assembly operations 5515Absolute Importance ( bij)44Relative Importance (ai*bij)188Requested value of sensory feedback ( ai*bij/5*bij)0.7manufacturing and quality control processes and of tol-erances variation on product functionalities.Students should also be able to recognize tolerance chains and identify the proper references.Professors in mechanical product design have been involved in the definition of the most significant activities and the lev-els of sensory feedback necessary to perform them.Table 1shows the necessary learning level of product functionaldesign and assembly principles and dimensional and geo-metric tolerances prescription.The evaluation values in the grey column are related to the importance that each activity represents for the learning process.The values in the side columns represent the sensory feedback required for performing every activity successfully,according to1–5scale.For example,it can be stated that the sense of sight is very important(the level is5)in assessing design solution alternatives while the sense of motion(3)and the sense of touch(1)are secondary.Hearing is useful in no way.On the contrary the functional and assembly errors detection involves the same three sensorial chan-nels but they all are key factors and gain an equal feed-back level(5).Absolute and relative importance values are calculated applying mathematical functions showed in table.Final values assess the level of sensory feedback requested to the proper VR set-up technology in order to support the concerning topic.In case study obtained feed-back values are equal respectively to0.87for functional and assembly principles learning and0.7for tolerances learning.An exhaustive description of the benchmarking method can be found in a previous research work where it was applied for identifying the VR system that better answers to design reviews activities requirements.Experimental results pointed out that most advantages in the use of VR are achieved when the technology is selected according to specific process char-acteristics and needs[19].At this point three different VR technologies combinations (C1,C2and C3)have been chosen for the assessment.C1is a single-user learning environment that consists of a head-mounted display(HMD)coupled with a common mouse. C2consists of a large volume display provided with ste-reo imaging and an optic tracking system that both improve visual perception of design solutions and create a collab-orative environment.C3associates a similar large volume display with afinger-based haptic device that gives force feedback and tactile perception of materials and compo-nents interaction.The evaluation method is based on a set of heuristics that are conveniently defined for virtual reality system context.Heuristics are grouped into three different dimensions(usability,presence and depth of sensation)as previously described.Each VR combination is evaluated by afive-point Likert scale[16].The method application allows the definition of a relative total value for every technological set-up(Fig.3).Comparing the obtained total values with the sensory feedback required by mechanical design learning topics it is possible to rec-ognize which technological combinationfits better for the specific purpose.The case study results highlight that C3combination is the best suited in supporting product functional design and assembly principles teaching while C2combination is the best suited in tolerances learning.If we would identify the combination that better answers to both topics,C3should be selected.Itsfinal value is the nearest to both requested feedback levels.4A structured experimental protocol to assess the learning process in mechanical product designIn order to verify the applicability of the proposed method and to test the main advantages connected with the use of the achieved VR technologies combinations,a structured experimental protocol is set.According to the educational standpoint it is worth to notice that learners’performances always depend on two main factors:the personal aptitude for specific subjects and the influence of the adopted hard-ware and software technologies.These two dimensions in mechanics education are strictly interconnected:it is difficult to distinguish their specific impact on the learning process. Therefore understanding how technology affects learning is a not a trivial task.In order to face this issue two evaluation levels are con-sidered inside the protocol:performance and usability.The first analysis aims at measuring the performances achieved by students during lessons and to quantify them in an objec-tive way.In this context time monitoring,error detection and learning curves could be useful indicators.The second anal-ysis aims at assessing the usability of the exploited support system.It can be stated that for learning scope a highly usable VR set-up is needed.4.1Performance analysisThe performance analysis is based on a set of objective met-rics and direct evaluation methods,such as user task analysis. Performance metrics are defined considering the main diffi-culties of students in mechanical product design learning. They are expressed by tangible entities,such as time and percentage mistakes,related to the following aspects:•assembly recognition capability,•assembly sequence identification,•assemblability error detection,•surfacefinishing comprehension,•design alternatives evaluation,•dimensional tolerances detection,•geometric tolerances detection,•mating type recognition,•tolerances chain comprehension,•geometrical tolerances impact.Each aspect represents a possible task for each mechanics education topic that is identified during the benchmarking。