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11 votes

Rotation matrix sign convention confusion.

I think that the main issue is that you're trying to read your rotation matrices from left to right. The sign changes seem random, but actually cycle in an ordinary way. Below follows a more elaborate ...
JJM Driessen's user avatar
10 votes
Accepted

Why do current manipulators tend to use 7 DoF instead of 6 DoF?

Adding a 7th joint, and still targeting a 6D pose, would result in a null space of at least one dimension anywhere in the workspace. That is basically one the reasons people may wish to use a 7-DOF ...
kucar's user avatar
  • 328
8 votes
Accepted

Cartesian Velocity Control between Two 3D Poses

You essentially want to find the time derivative of a linear interpolation between two rotations. The easiest way to obtain this would probably to convert the rotation matrix between the two ...
fibonatic's user avatar
  • 941
7 votes

Computing the Jacobian Matrix -- chain rule?

Writing the equations by hand and deriving them is certainly the best way to understand what is happening "in the background". Generating the equations and deriving them using a syombolics engine, ...
50k4's user avatar
  • 6,682
7 votes
Accepted

Is there a way to determine which degrees of freedom are lost in a robot at a singularity position by looking at the jacobian?

Not by merely looking at Jacobian but by looking at the Singular Value Decomposition of the Jacobian, one can see the degrees of freedom that are lost, if lost. Of course it technically somehow turns ...
Suneesh Jacob's user avatar
6 votes
Accepted

inverse kinematics for 6 jointed robots

I would recommend changing the naming convention since it is a bit misleading. In robotics the world Coordinate system (CS) is usually your fixed, absolute coordinate system. Lets call the ...
50k4's user avatar
  • 6,682
6 votes

Programming Inverse Kinematics in C++

I agree with SteveO that there is nothing wrong with reinventing the wheel if you want to learn about wheels. And for a single application, 4 DoF arm, the IK is probably not too hard. But I feel ...
Ben's user avatar
  • 5,865
6 votes
Accepted

Why are joint velocities very high near a singularity?

First of all, singularities are not configurations that have the same end-effector position and orientation. Those configurations are inverse kinematic (IK) solutions to that end-effector pose (...
Petch Puttichai's user avatar
6 votes

Inverse kinematics for differential robot knowing linear and angular velocities

Your linear velocity should be the average of both wheel values. Assuming there's some wheel radius of WHEEL_RADIUS, as you've stated, then you should get each ...
Chuck's user avatar
  • 16k
6 votes
Accepted

Why with the pseudo-inverse it is possible to invert the Jacobian matrix even in a singular configuration?

The pseudoinverse gives a “least squared error, minimum-norm” solution: Out of all $\dot{q}$ vectors at your current $q$, the vector $$\dot{q}_{s} = J^{+}(q)\dot{p}_{\text{in}}$$ satisfies two ...
RLH's user avatar
  • 619
5 votes

is it possible to get all possible solutions of inverse kinematics of a 6 DOF arm?

I suggest you look at Craig's book Introduction to Robotics Mechanics and Control. In the inverse kinematics chapter he addresses the multiple closed-form solutions obtained analytically. Many other ...
SteveO's user avatar
  • 4,396
5 votes
Accepted

Programming Inverse Kinematics in C++

It is rather straightforward to implement inverse kinematics for a particular manipulator in C++. Of course, you need to begin with the inverse kinematic equations themselves. Putting those into ...
SteveO's user avatar
  • 4,396
5 votes
Accepted

Does Inverse Kinematics need the current joint angles?

It depends on the method that you use for computing an IK solution. If you have an analytic formula for IK solutions then you do not need the current joint values of the robot. You just plug in the ...
Petch Puttichai's user avatar
5 votes

How do CAD programs solve for Inverse/Forward Kinematics problem in Assembly?

EDIT: Improved based on the comments below. If you have a CAD assembled, that means that you have one valid configuration given. You move the TCP (Tool Center Point) only a small amount, since your ...
50k4's user avatar
  • 6,682
5 votes

Inverse Kinematics problem formulation (optimization)

The formulation is typical for redundant robots, in which there are an infinite number of joint velocity vectors that could satisfy the $\dot{r}_{t}$ goal. In the version you cite, the $Q$ matrix ...
SteveO's user avatar
  • 4,396
5 votes

Struggling to understand Jacobian Inverse Kinematics

You will find it helpful to keep the physical robot and the math separate. The kinematics equations map joint parameters (which are often grouped as a vector $q$) to Cartesian coordinates ($x$,$y$,$z$...
hauptmech's user avatar
  • 4,445
5 votes
Accepted

How do I find the inverse kinematics of a 5-DOF manipulator having the following DH parameters?

A general IK solution is not possible for an arm with less than 6 joints. You can move the gripper to any point (within reach) but you can't completely control the orientation. If you fix the ...
Peter Corke's user avatar
  • 1,702
5 votes

Can workspace of a manipulator change after considering its dynamics?

The workspace of a manipulator is strictly determined by its kinematics. Since kinematics only consider the geometry of motion, without regard to forces and torques needed to accomplish tasks, you ...
SteveO's user avatar
  • 4,396
5 votes
Accepted

Velocity-Control of a manipulator without a dynamic model

Your intuition is partially correct in the sense that you ought to go with position control implemented via velocity commands resorting to a kinematic (not dynamic) model of the manipulator. This can ...
Ugo Pattacini's user avatar
5 votes
Accepted

Solving inverse kinematics with non-linear optimization libraries

Is it a good idea to solve inverse kinematics with non-linear optimization libraries such as Ceres? Yes, definitely! The trend in literature during the last years is to walk away from the traditional ...
Ugo Pattacini's user avatar
5 votes

How to control a 4 wheel mechanum wheel robot with PID?

Let's consider first the task you are wanting to accomplish: following some sort of Cartesian space trajectory. So, you are wanting to make sure your robot is only moving in the x-direction. However, ...
domo_arigato's user avatar
4 votes

Denavit Hartenberg parameters - 3DOF articulated manipulator

I defined the robot using your (assumed standard) DH parameters: ...
Peter Corke's user avatar
  • 1,702
4 votes

Human arm inverse kinematics

You are tackling two non trivial problem at the same time 1. Inverse kinematics of an overactuated manipulator 2. Obstacle avoidance using the null space By definition of the null-space projection ...
N. Staub's user avatar
  • 1,412
4 votes

Solving Inverse Kinematics with Gradient Descent

There are more approaches to solve the inverse kinematics equations. If you want to continue to use the pseudo-inverse based approach and still obtain more then 1 solution you can flip the sign of ...
50k4's user avatar
  • 6,682
4 votes
Accepted

Do DH parameters change for a scaled robot 3d model?

You will need to provide target coordinates (x,y,z, etc) to your inverse kinematics equations. As long as they have the same scale as your DH parameters, the joint angles calculated will be the same. ...
hauptmech's user avatar
  • 4,445
4 votes

Is there any C++ library I could use to program a robotic manipulator involving forward and inverse kinematics?

The best way to understand forward and inverse kinematics is to write a library for its own. A good starting point is to implement Cyclic Coordinate Descent. So called "ready-to-run" librarys like ...
Manuel Rodriguez's user avatar
4 votes

Matlab Inverse Kinematics 6 DOF

Ideal solution can be defined in many ways. The simplest way to choose one is to compare which of the 8 solutions is closest to your current pose in joint space. This is usually a good idea if you ...
50k4's user avatar
  • 6,682
4 votes

Self-Motion Manifolds

Saw this question and figured I would throw my two cents in 5 years later. Gilhad's reasoning about the mathematical process of simple to complex theorems/proofs makes sense as to why the analysis is ...
domo_arigato's user avatar
4 votes
Accepted

Inverse kinematic orientation problem

Up till now, I am using the Euler angle representation but I have not been successful. After referring to the book "Robotics Modelling, Planning and control" by Bruno Siciliano form Springer ...
manan kalsariya's user avatar
4 votes

How do I find the inverse kinematics of a 5-DOF manipulator having the following DH parameters?

If you say you're are stuck after values for the first two angles, you are probably trying an analytical approach. Try solving for IK using standard techniques Jacobian Pseudo Inverse or Cyclic ...
Akshay Kumar's user avatar

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