Use OMPL for UR5

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Juzhan
Posts: 3
Joined: 30 Aug 2021, 03:01

Use OMPL for UR5

Post by Juzhan »

I want to generate a collision-free path with OMPL and ik on my UR5 robot, so I convert some code from scenes/pathPlanning/path_planing_and_grasp.ttt.

But in my code, it is slow and difficult to compute a valid goal config. Even the code can find a goal config, the path generates by simOMPL will collision with the floor. And how should I check the self-collision in UR5, when I set the collisionParis = { collection, collection }, the code can't find any solution. Could you help me to check the code? The main function is generatePath() in UR5 script. Here is the scene file:
https://github.com/Juzhan/UR5_test

By the way, if the robot grasps a box with a gripper, how should I set the box to be a part of the robot for collision-free planning?

Thanks in advance!

coppelia
Site Admin
Posts: 8975
Joined: 14 Dec 2012, 00:25

Re: Use OMPL for UR5

Post by coppelia »

Hello,

it appears that your robot is in constant self-collision state. Try this:

Code: Select all

function sysCall_init()
    robot = sim.getObjectHandle(sim.handle_self)
    collection=sim.createCollection(0)
    sim.addItemToCollection(collection, sim.handle_tree, robot, 0)
end

function sysCall_sensing()
    -- Check for self-collision:
    local res, collidingObjects=sim.checkCollision(collection,collection)
    if res>0 then
        print(string.format("Self-collision: Objects %s and %s",sim.getObjectName(collidingObjects[1]),sim.getObjectName(collidingObjects[2])))
    end
    -- Check collision with environment:
    local res, collidingObjects=sim.checkCollision(collection,sim.handle_all)
    if res>0 then
        print(string.format("Robot-environment collision: %s and %s",sim.getObjectName(collidingObjects[1]),sim.getObjectName(collidingObjects[2])))
    end
end
and you will quickly see what is in collision. You can also check the color of the colliding objects:

Code: Select all

function changePairColor(entityPair,colorPair)
    originalColorData={}
    originalColorData[1]=sim.changeEntityColor(entityPair[1],colorPair[1])
    originalColorData[2]=sim.changeEntityColor(entityPair[2],colorPair[2])
end

function restorePairColor()
    if originalColorData then
        sim.restoreEntityColor(originalColorData[1])
        sim.restoreEntityColor(originalColorData[2])
        originalColorData=nil
    end
end

function sysCall_init()
    robot = sim.getObjectHandle(sim.handle_self)
    collection=sim.createCollection(0)
    sim.addItemToCollection(collection, sim.handle_tree, robot, 0)
    collisionColors={{1,0,0},{1,0,1}} -- collider and collidee
end

function sysCall_cleanup()
    restorePairColor()
end

function sysCall_sensing()
    -- Check for self-collision:
    local res, collidingObjects=sim.checkCollision(collection,collection)
    restorePairColor()
    if res>0 then
        print(string.format("Self-collision: Objects %s and %s",sim.getObjectName(collidingObjects[1]),sim.getObjectName(collidingObjects[2])))
        changePairColor({collidingObjects[1],collidingObjects[2]},collisionColors)
    else
        -- Check collision with environment:
        local res, collidingObjects=sim.checkCollision(collection,sim.handle_all)
        if res>0 then
            print(string.format("Robot-environment collision: %s and %s",sim.getObjectName(collidingObjects[1]),sim.getObjectName(collidingObjects[2])))
            changePairColor({collection,collidingObjects[2]},collisionColors)
        end
    end
end
Cheers

Juzhan
Posts: 3
Joined: 30 Aug 2021, 03:01

Re: Use OMPL for UR5

Post by Juzhan »

Thanks! I adjust the size of some parts of the UR5 model, now I can find the path when collisionParis = { collection, collection }. But I use the UR5 model directly from the Model browser, maybe you can modify the UR5 model in the next software update to avoid self-collision.

coppelia
Site Admin
Posts: 8975
Joined: 14 Dec 2012, 00:25

Re: Use OMPL for UR5

Post by coppelia »

Instead of adjusting the model itself, you could have just adjusted the Collection self-collision indicator.

Cheers

Juzhan
Posts: 3
Joined: 30 Aug 2021, 03:01

Re: Use OMPL for UR5

Post by Juzhan »

Thanks a lot!

And I still have 2 questions.

1. UR5 robot has an initial child script, which contains a function coroutineMain(). And I also wrote a path planning and execution function in the child script.
If I want to use the path planning and execution function, I have two methods to do this:
(a) use the function directly in coroutineMain,
(b) use the function via Python remoteAPI.
Method (a) can generate a stable movement when executing the path but the path planning is much slower than method (b). Method (b) can plan the path very quickly but the execution is too fast even cause some swing of the robot arm. I try to reduce the maxVel, maxAcc, and maxJerk but they didn't work.
What might have happened when I use these two methods? I think both of these methods should perform the same on planning and on execution.

2. I am working on the bin packing problem, I put some closely placed objects in a scene. After I grasp an object, I add the grasped object into the robot collection via sim.addItemCollection for collision detection. But the object is in contact with other objects, so the grasped object is a collision with the scene and I can't plan a path moving with the grasped object. Is there any way to avoid this problem, like adjust the detection-sensing or collision volume?


Cheers

coppelia
Site Admin
Posts: 8975
Joined: 14 Dec 2012, 00:25

Re: Use OMPL for UR5

Post by coppelia »

If you run some code in a coroutine/thread, then that code can often be interrupted (since it is a thread/coroutine!). To avoid that, you can have a section that forbids automatic thread switches:

Code: Select all

    local l=sim.setThreadAutomaticSwitch(false) -- temporarily forbid automatic thread switching
    ...
    -- execute here some task without interruption
    ...
    sim.setThreadAutomaticSwitch(l) -- restore the original automatic thread switching
Now, if you try to execute a movement from a remote API client, or from any other external application, then simply trigger the execution from there, but do not directly execute the movement. Let the thread handle this. e.g. here an extremely simple example:

Code: Select all

...

function legacyRemoteApi_triggerMovement(intData,floatData,stringData,buffer)
    -- prepare the moevement data here, e.g.
    movementData={}
    movementData.goalPosition=floatData
    return {},{},{},''
end

function coroutineStart()
    while true do
        if movementData then
            -- execute the movement here
            movementData=nil
        end
    end
end
For a more elaborate example, have a look at the demo scene scenes/messaging/movementViaRemoteApi.ttt (that scene runs with a client Python application you can find in the programming/remoteApiBindings, programming/b0RemoteApiBindings or programming/zmqRemoteApi folders.

About your second question: maybe simply do not add the object to the collection? You can define many different collections, e.g. your robot, the environment, the environment minus the part to grasp, etc. Then simply check the appropriate collision pairs (e.g. robot collection vs environment collection).

Cheers

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