Assembly Simulation on Collaborative Haptic Virtual Environments Rosa
Assembly Simulation on Collaborative Haptic Virtual Environments Rosa Iglesias, Elisa Prada Sara Casado, Teresa Gutierrez Ainhoa Uribe, Alejandro Garcia-Alonso Fundacion Labein Universidad del Pais Vasco (UPV-EHU) /18
Outline • Objectives • Haptic devices, haptic rendering • Haptic Assembly Simulation • Collaborative Haptic Assembly Simulation • Network Topologies • Client/Server (two implementations) • P 2 P • Conclusions
Collaborative Haptic V Environment for Assembly Tasks GOAL: Create a Distributed Virtual Environment for collaboration, whereby users can carry out assembly and maintenance tasks • VE Assembly + simultaneously + haptic devices • to design and evaluate computer generated mock-ups prior to building any physical prototype.
Haptic devices
Haptic rendering • “Haptic rendering is the process of computing and generating forces in response to user interactions with virtual objects” (Salisbury, 1995). • “Haptic rendering allows users to “feel” virtual objects in a simulated environment” (Salisbury, 2004) – To touch objects, move them, … – To create different haptic effects: texture perception, deformable elements or collision impacts. • Haptic devices require an update frequency of 1000 Hz.
Haptic rendering • An update frequency of 1 KHz means: Haptic loop
Haptic assembly simulation (HAS) • Description video
Introduction: HAS • Examples of assembly constraints: – Assembly along an axis – Assembly along a common plane
Haptics require new architectures • Classical simulation loop : – Process input events (move objects) – Simulation – Image rendering – Haptic rendering ? ? ? it is not possible • Due to high frequency of haptic rendering: required two independent processes (threads).
HAS : two processes Simulation (20 -60 Hz) Haptic (1000 Hz) • Get last position • • Simulation (collisions, constraints, …) Image rendering • • • Send “haptic requirements” • Read last position (from haptic device) Send last position “haptic requirements” received ? Compute force (haptic rendering) Send force to haptic device Problems : (1) haptic cycles without simulation updates, (2) updates mean brusque changes (haptic feedback instability)
Objectives & Challenges - Broad objective: Several users can work simultaneously to achieve a common goal using haptic devices in assembly operations. - Challenges: • Consistency (virtual scene synchronization) must be guaranteed, because users simultaneously interact with the same scene • Effective and stable haptic feedback when users collide or assemble their grasped objects. • Scalability: number of users, virtual objects and so on.
Objectives & Challenges • KEY FACTOR: Network conditions – Delay – Variation of delay (jitter) – Message Loss, …. • They affect: VE consistency and user perception – Visually: • Sluggish scene update of the remote object – Haptically • Unstable haptic feedback
Objectives & Challenges in CHAS • GOAL: Collaborative Haptic Assembly Simulator (CHAS), whereby two users can simultaneously carry out assembly tasks using haptic devices. • Two types of interaction: – INDEPENDENT INTERACTION: interacting with static objects (not grasped). – DEPENDENT INTERACTION: depends on other user’s action.
Objectives & Challenges in CHAS • Two types of dependent interaction: – Dependent collision: when both grasped objects collide – Remote assembly: when a grasped object is being assembled into other grasped object CHALLENGES in CHAS In the case of a remote assembly + dep. coll. : • consistency must be guaranteed. • each user must receive adequate haptic feedback
Network topology To build a distributed VE: Client/Server (C/S) Peer-to-Peer (P 2 P) C/S Mixture of them Multiple Servers P 2 P /18
Client/Server (A 1) • PROS: Consistency is automatically satisfied, since data are validated centrally, and then distributed to clients. • CONS: computations for simulation are Simulation made sequentially Simulation or validation: check if new object position is colliding or computes the assembly constraints A 1
Client/Server (A 3) Observing its disadvantage: sequential computation. A new C/S architecture was designed. • PROS: well-balanced distribution of the workload and parallel computation. • CONS: efficiency comes from the worst Consistency computer conditions Consistency: server checks if there is any inter-object penetration. In that case, synchronise user’s scenes Simulation A 2
Network topology: Analysis using C/S RESULTS using C/S architectures: • With A 1 and A 3: several users can simultaneously interact using keyboard/mouse. • A 3 seemed to have better performance when > 2 users • A user can haptically interact while others watch with A 3. • After experiments, it was shown that simulation/validation must be placed at each user for avoiding unstable haptic feedback, even with independent interaction. • A 1 and A 3 are very sensitive to the network delay.
Network topology: Analysis using C/S • They address: – collaboration taking turns (any delay) – cooperative manipulation = a carrying task • Two users grasping the same object. • Only low-delay interaction between both users, because haptic interaction is affected. • Two goals still not achieved : – simultaneous assembly tasks – high delay
Network topology: Analysis C/S vs P 2 P Comparing C/S and P 2 P: • C/S: Consistency is more easily achieved. Local scene update after a round-trip delay to the server. • P 2 P: Consistency challenge. Update delay is only one-way - Updates are less dependent on network conditions. - Permit a better performance with haptic interaction. - Potential to scale to a larger number of users. Then, a P 2 P architecture is chosen
Consistency-maintenance scheme • In our research, to build the Collaborative Haptic Assembly Simulator (CHAS), CHAS whereby two users can simultaneously carry out assembly tasks using haptic devices. • A new consistency-maintenance scheme has been designed and tested.
Consistency-maintenance scheme Main features: • Gives priority to the validation of interactions between objects grasped by users for fast haptic response. • Small messages size: < 200 bytes • Not need to store and manage a history of movements. • Not specific messages to deal with inconsistency because each user manages consistency locally.
Experimental set-up • Many experiments were carried out varying end-toend delays: less than 1 ms, 50 ms, 100 ms, 200 ms and with jitter (0 ms – 100 ms). • The experimental platform:
Experimental set-up • The experimental platform: – Experimental platform: 3 computers via a 100 Mbps links connected by two high-speed switches. – Two computers are each connected to an OMNI device. – The other computer to simulate the different values of delay and jitter.
Results between Labein & QUB: VE & tasks Virtual scene: Electrical box for an aircraft engine • User Labein grasps the handle • User Queen’s grasps the screw • Perform collisions • Assemble both grasped objects CAD design: Electrical box for an aircraft engine by SENER
Results between Labein & QUB: Consistency • Consistency after a dependent collision
Results between Labein & QUB: Forces • Collision force magnitude after a dependent collision
Results between Labein & QUB: Forces • Force magnitudes during a remote assembly
Results between Labein & QUB: Conclusions • With the consistency-maintenance scheme in CHAS, users had a realistic sensation of the VE and the performance was satisfactory. • CHAS provided an adequate haptic interaction when both users perform remote assemblies or dependent collisions. • Such haptic feedback showed that the sense of co-presence between the users continue to improve, with regard to only visual feedback.
THE END QUESTIONS ? THANK YOU VERY MUCH ! MUCHAS GRACIAS ! ESKERRIK ASKO !
DONOSTIA-SAN SEBASTIAN
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