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 ...
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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 ...
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  • 306
8 votes

Computing inverse kinematic with jacobian matrices for 6 dof manipulator

Disclaimer! I will try to solve your problem but it may or may not solve the problem with your code! TL;DR: Two possible mistake in your code. In your pseudo-code, you are using transpose of ...
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  • 226
8 votes

Forward kinematic and inverse kinematic... When to use what?

Forward kinematics uses joint angles (with known link lengths) to compute the tool position and orientation. Inverse kinematics uses tool position and orientation, to compute joint angles. Note: if ...
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  • 4,326
8 votes
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Forward kinematic and inverse kinematic... When to use what?

Let me give you a mathematician's perspective on the difference between the two kinds problems. Forward kinematics asks the question: given a certain input (i.e. control command), what will be the ...
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  • 1,238
7 votes
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Is the geometric inverse problem's solution "continuous" for a redundant robot?

I don't know if there is a formal proof to this, but in general, no the set of all possible joint configurations that correspond to a particular end-effector pose is not continuous. I think of the ...
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  • 5,215
7 votes
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Can a Jacobian be used to determine required joint angles for end effector velocity/position?

Yes, the Jacobian relates the joint velocities to end-effector velocity through this equation: $$ \mathbf{v}_e = \mathbf{J}(\mathbf{q}) \dot{\mathbf{q}} $$ Where $\mathbf{q}$ is the joint angles, $\...
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  • 5,215
7 votes
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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 ...
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7 votes
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Finding Center of Mass for Humanoid Robot

Yes. As @hauptmech mentioned, you can use your forward kinematics to get the center of mass of each link in the base frame. Then you can simply compute the weighted average of the masses and ...
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  • 5,215
7 votes
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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 ...
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  • 921
6 votes
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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 ...
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  • 6,322
6 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, ...
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  • 6,322
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 ...
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  • 5,215
6 votes
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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 (...
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6 votes
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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 ...
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  • 609
5 votes
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Inverse Kinematics of Parallel Manipulator (Delta Robot)

For these sorts of problems, I always like to attempt to solve them myself. And they're surprisingly simple when you think about them geometrically. Parallel mechanisms are especially easy because ...
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  • 6,337
5 votes

2D Robot Arm Inverse Kinematics with minimum joint loads

Kawato M. Developped the technique called the Minimum Commanded Torque and Minimum Commanded Torque Change to optimize joint ...
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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 ...
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  • 4,326
5 votes
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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 ...
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  • 4,326
5 votes
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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 ...
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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 ...
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  • 6,322
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 ...
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  • 4,326
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 ($x$,$y$,$z$...
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  • 4,205
5 votes
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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 ...
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  • 1,522
5 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 ...
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  • 14.6k
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 ...
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  • 4,326
5 votes
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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 ...
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4 votes

7DOF inverse kinematics spherical wrist

I believe kinematic decoupling used to be the standard procedure for 6 DOF arms. (6R with spherical wrist). Where you would solve the 3 DOF position IK first, then 3 DOF orientation IK. If you ...
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  • 5,215
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 ...
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  • 1,327
4 votes

Finding inverse kinematics algorithm for a specific manipulator

To expand on Ugo's answer, some libraries that implement these general IK algorithms: OpenRave ROS MoveIt! Matlab Robotics Toolkit Orocos For people just starting out with kinematics, I highly ...
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  • 5,215

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