Increasing Accuracy of Industrial Robots in Machining of Carbon Fiber Reinforced Plastics

Flatness Based Control of an Industrial Robot Joint Using Secondary Encoders

“…Considering elastic joints it is difficult to precisely calculate the motor reference signals since the equation = is only valid for rigid joints. A precise calculation of the motor reference signals requires the full, nonlinear stiffness model ( 1) and (2). Therefore, the exact calculation of the motor reference signals is sensitive to modelling errors.…”

“…/ g e t p a r a m e t e r s f o r e a c h a x i s / / / l i n k i n e r t i a , kgm ^2 M_i = M[ i _ a x ] ; / / m o t o r i n e r t i a , kgm ^2 J _ i = J [ i _ a x ] ; / / b a c k l a s h a n g l e , r a d qB_i = qB [ i _ a x ] ; / / C o r i o l i s and c e n t r i p e t a l t o r q u e , Nm t a u _ c _ i = t a u _ c [ i _ a x ] ; / / g r a v i t y t o r q u e , Nm t a u _ g _ i = t a u _ g [ i _ a x ] ; / / a c c e l e r a t i o n t o r q u e , Nm t a u _ a _ i = t a u _ a [ i _ a x ] ; / / t r a n s m i s s i o n f a c t o r , w i t h o u t u n i t u _ i = u / g e t v a r i a b l e s f o r e a c h a x i s / q 0 _ i = q0 [ i _ a x ] ; / / l i n k a n g l e q 1 _ i = q1 [ i _ a x ] ; / / l i n k v e l o c i t y q 2 _ i = q2 [ i _ a x ] ; / / l i n k a c c e l e r a t i o n q 3 _ i = q3 [ i _ a x ] ; / / l i n k j e r k q 4 _ i = q4 [ i _ a x ] ; / / l i n k j e r k d e r i v a t i v e / c o m p u t e f e e d f o r w a r d t o r q u e , m o t o r a n g l e and m o t o r v e l o c i t y / t [ 0 ] = M_i * q 2 _ i ; t [ 1 ] = M_i * q 3 _ i ; t [ 2 ] = M_i * q 4 _ i ; t [ 3 ] = f _ v _ i * q 1 _ i ; t [ 4 ] = f _ v _ i * q 2 _ i ; t [ 5 ] = f _ v _ i * q 3 _ i ; t [ 6 ] = q 1 _ i * s F _ i ; t [ 7 ] = q 2 _ i * q 2 _ i ; t [ 8 ] = s E _ i * s E _ i ; t [ 9 ] = s F _ i * s F _ i ; t [ 1 0 ] = − f _ c _ i ; t [ 1 1 ] = 1 . 0 / c _ i ; t [ 1 2 ] = t [ 6 ]…”

“…Industrial robots are highly flexible due to their open and complex kinematic chain and are mainly designed for a good repeatability but not for high precision tasks, such as milling [1]. The main drawback of using an industrial robot in machining processes is the lack of high position accuracy caused by low stiffness, meaning low eigenfrequencies and joint elasticity between the actuators and the driven links [2,3]. As a result, conventional computerized numerical control (CNC) machines, possessing high stiffness and simple kinematics, can still not be replaced by industrial robots for machining tasks [4,5].…”

“…The impact of backlash caused by transmission drives was recognized by [24] in his experimental study of harmonic drive, showing that torque transmission has a nonlinear characteristics and the input torque can not be entirely transmitted to the driven link. The impact of backlash is also investigated and modeled in [2,25]. The authors in [23] show a considerable improvement in milling accuracy of aluminium by taking into account backlash effects and all joint flexibilities.…”