The Research of 7 Degrees of Freedom Robotic Manipulator

The robotic manipulator has been widely utilized in Automatic Production Line. Typical robotic manipulator which has six degrees of freedom makes end effector do three orientation translation and rotation. Human arm which is more dexterous than typical robotic manipulator has seven degrees of freedom which make human do more complex movement. In some application, for example curve welding, because of narrow workspace and complex movement, it is appropriate that we use seven degrees of freedom.

iCeiRA Lab had designed mechanism, system structure and control algorithm about seven degrees of freedom on July. The photo shows that iCeiRA Lab designed the first seven degrees of freedom called “iCeiRA Arm”.



Arm Design

The abstract:

It is used to be equipped the force sensor on the end effector to measure strength and the other places couldn’t experience force strength when extra force toughed. Based on safe and application, the design will be all place are able to measure. It is just like human arm. The first to fourth about iCeiRA Arm have torque sensors which make arm suffer component of extra force and noise reduce. In addition, the end effector is equipped the six degrees of freedom force sensor. Moreover, not only the end effector but also shoulder can measure information to compute from sensor.

Worm Joint:

iCeiRA Arm use seven degrees of freedom and Worm Harmonic Drive, so all circuits can pass through form rotation center that make circuit simple and joint rotate 360 degree.


Control Algorithm

On-line trajectory planning:

Online trajectory planning contains smooth trajectory planning and online inverse kinematic.

Smooth trajectory planning generates new position command in every servo time according to object position, the trajectory planning from the series command satisfy the maximum speed and move with the acceleration we set. Whatever the object position is, the end effector move with the acceleration we set and continuous speed. After generating position command, online inverse kinematic will get every joint angle and can compute redundant degrees of freedom.

Redundant degrees of freedom control:

Seven degrees of freedom arm is redundant arm. When we give the position orientation, arm can have unlimited poses to satisfy. Like this picture, when the end effector is fixed, elbow can be any position of redundant circle. Redundant freedom control is able to control the end effector to move and manipulate elbow in redundant circle simultaneously. In addition, redundant freedom control can do optimal arm pose.

It is immediate computation that iCeiRA Arm with redundant degree of freedom do experiment, therefore, we can manipulate the arm without planning trajectory function.

The function is applied in unknown information perception, for example, manipulator vision.

Redundant arm control in arm plane will be persistently researched and we will use force sensor to research redundant arm impedance control and mixed position force control and it will be combined the image processing which will be a function that can make intelligent arm catch things automatically.iCeiRA lab has developed robotic system persistently, the second of arm is planning now.



1.Seven degrees of freedom robotic arm

If iCeiRA Arm is typical six degrees of freedom robotic arm, it will not catch things because of colliding obstacle. However, if iCeiRA Arm is seven degrees of freedom robotic arm, it will be controlled with redundant degrees of freedom to move and successfully catch things and avoid obstacle with new pose.

2.Fix the end effector

The position of the end effector of iCeiRA Arm isn’t move, but the orientation continuously changes. This displays seven degrees of freedom robotic arm dexterous.