Joint callback functionsScripts can include a joint callback function, which is one of many system callback functions. When present for a given joint, then it will be called by CoppeliaSim in various situations: Joint callback functions enable the user to customize the control loop for specific joints in order to write low-level control algorithms. Following represents a simple position control joint callback function, for a joint in dynamic mode:
function sysCall_joint(inData)
-- inData.mode : sim.jointmode_kinematic or sim.jointmode_dynamic
--
-- inData.handle : the handle of the joint to control
-- inData.revolute : whether the joint is revolute or prismatic
-- inData.cyclic : whether the joint is cyclic or not
-- inData.lowLimit : the lower limit of the joint (if the joint is not cyclic)
-- inData.highLimit : the higher limit of the joint (if the joint is not cyclic)
-- inData.dt : the step size used for the calculations
-- inData.pos : the current position
-- inData.vel : the current velocity
-- inData.targetPos : the desired position (if joint is dynamic, or when sim.setJointTargetPosition was called)
-- inData.targetVel : the desired velocity (if joint is dynamic, or when sim.setJointTargetVelocity was called)
-- inData.initVel : the desired initial velocity (if joint is kinematic and when sim.setJointTargetVelocity
-- was called with a 4th argument)
-- inData.error : targetPos-currentPos (with revolute cyclic joints, the shortest cyclic distance)
-- inData.maxVel : a maximum velocity
-- inData.maxAccel : a maximum acceleration
-- inData.maxJerk : a maximum jerk
-- inData.first : whether this is the first call from the physics engine, since the joint
-- was initialized (or re-initialized) in it.
-- inData.passCnt : the current dynamics calculation pass. 1-10 by default
-- inData.rk4pass : if Runge-Kutta 4 solver is selected, will loop from 1 to 4 for each inData.passCnt
-- inData.totalPasses : the number of dynamics calculation passes for each "regular" simulation pass.
-- inData.effort : the last force or torque that acted on this joint along/around its axis. With Bullet,
-- torques from joint limits are not taken into account
-- inData.force : the joint force/torque, as set via sim.setJointTargetForce
if inData.mode==sim.jointmode_dynamic then
-- Simplest position controller example:
local ctrl=inData.error*20
local maxVelocity=ctrl
if (maxVelocity>inData.maxVel) then
maxVelocity=inData.maxVel
end
if (maxVelocity<-inData.maxVel) then
maxVelocity=-inData.maxVel
end
local forceOrTorqueToApply=inData.maxForce
-- Following data must be returned to CoppeliaSim:
local outData={vel=maxVelocity,force=forceOrTorqueToApply}
return outData
end
-- Expected return data:
-- For kinematic joints:
-- outData={pos=pos, vel=vel, immobile=false}
--
-- For dynamic joints:
-- outData={force=f, vel=vel}
end
In Python, a joint callback function can only be implemented via a non-threaded script, and it should be explicitly activated with a luaExec command:
#python
#luaExec additionalFuncs={'sysCall_joint'}
def sysCall_joint(inData):
pass
A joint callback call is applied to all scripts located in the upward hierarchy of the joint, and interrupted as soon as a script handles the call, i.e. returns data: [Script execution precedence with a joint callback] |