A question about kinematic parameters

[Bora_2]

Hello everyone, 

I'm using Labview Robotics module and i was trying to build my robot to calculate forward kinematics.

I tried to initialize generic serial arm by using DH parameters. According to DH parameters of the robot, length(a) of the third joint should be negative (the axis should be below of the Joint 4). If i give ''-'' length , program doesn't response.

After that, I tried to assign frames and fill the DH table using different rotations and translations, but I couldn't do this because theta had no effect on the rotation of the Z axis. 

How can i fix this problem ? ( Can i give ''-'' length somehow ? Or do you have other suggestions ?)

I don't know exactly how to achieve this and any help would be greatly appreciated. 

Thank you,

Bora

[MarinaBen]

Hello,

You are actually throwing an error at your Initialized Serial Arm.vi when you give a negative length. This VI does not allow for the length to be negative.

[Bora_2]

Hello Marina,

Thank you for the reply

Actually, you are right. According to specifications of kinematic parameters in Initialize generic serial arm.vi, length can not be negative . In that case, i can assign frames and fill DH table w.r.t. this property. However, theta (it is variable but we can add π/2 or we can subtract π/2  from this variable in order to rotate frames around Z and after this operation, we can get X direction) Also, theta doesn't work. For the reasons mentioned above , i couldn't solve this situation and i don't know how to build my model correctly ? 

(  If this vi. doesn't allow me to give ''-'' length, i can use different DH parameters that have positive lengths. However, If i can not define the angle between X axes by using theta without negative length property, i can say that solution is almost impossible )

Regards,

Bora