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Questions tagged [manipulator]

manipulator is a device used to manipulate materials without direct contact.

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Simulate joint holding in gazebo

I am building a simulation of a custom-designed robotic arm. In the simulation, I am controlling it using 'effort_controllers/JointVelocityController'. However, I want the joint to remain still when ...
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136 views

DH parameters of a serial manipulator RRRRRR

I am trying to find the forward kinematics of this manipulator in the picture using DH notation. All of the joints are rotational. I managed to get to the third joint. The parameter table is below. ...
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How to choose drives for a 6Dof manipulator with a shperical wrist

So my question I guess is tied to design or modelling(Not too sure what topic it falls under) a manipulator according to what I read in the book "Introduction to robotics:mechanics and control&...
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1 answer
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Collision Update on a Manipulator Links

I am trying to apply a pick-and-place operation with the Fanuc 6 DOF robot. I am using Moveit2 to give motion planning commands to robot. It sometimes gets into limit error during the execution of ...
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Designing the kinematics and Dynamics of a spherical joint as 3 revolute Joint

I am working on a project where I am trying to mimic human like motion and for that I am designing a 7 DOF arm with the spherical joint in shoulder as 3R joints and 2R joints for elbow and 2R joint ...
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1 answer
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How to model the Cable composites in Mujoco Physics Simulation engine

How to name the cable composite in mujoco, also how to add equality constraint to the end of the cable with another body ?
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Can't visualize pre-defined pose in RViz

quite new to ROS. I'm trying to program the trajectory for a 3DoF manipulator using MoveIt! I have been able to visualize it in RViz using MoveIt setup assistant and made sure to setup planning groups,...
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1 answer
435 views

Robotic Manipulator 3-RRP v2

I recently asked a question about a 3-RRP manipulator but the only answer didn't work for my robot. I would describe the manipulator as an arm that rotates around the shoulder over the x-y axis, the ...
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103 views

When assigning frames in Denavit-Hartenberg (DH) parameters, where do I put the frame on end effector?

I have a simple question, for the last link (end effector) I need to estimate the parameters but when I put the reference frames in the center of the end effector, I just don't know. Last link (end ...
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Control Manipulator/Gripper through EGM Communication ABB

I am a university student and new to robotics. I am part of a semester project where the goal is to directly control the gripper of the robot. The gripper is pneumatic and can be controlled with RAPID ...
1 vote
1 answer
495 views

How to calculate operating torque and holding torque of a slew drive for a manipulator arm?

Hope you are doing good and enjoying your weekend. I have a question regarding calculation of torque and tilting moment for a slew drive. Slew drive (motorised) will be used at the base of a ...
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129 views

Cant control OpenManipulator on Turtlebot3

I'm using the OpenManipulator on the Turtlebot3 together with Ubuntu 22.04 and ROS2 Humble. When I start the bringup for the manipulator it looks like this: ...
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Bot orienting to same direction regardless of Quaternion value in Moveit

I am trying to control a simulated UR5e bot using ROS. For trajectory planning and execution i am using Moveit. The issue is that when I give a Pose to Moveit, the bot reaches the position (XYZ) just ...
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Open Manipulator python API documentation, or Examples

As stated by the title, is there a way I can access to the python API documentation of the Open Manipulator package? Right now all I can find are service definition such as: https://emanual.robotis....
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1 answer
299 views

How to define the degrees of freedom of a flexible manipulator?

Consider a cable-driven flexible manipulator which has 3 cables. Consider the 3 cables to be actuated by 3 motors. Assume that by pulling the three cables in different configurations, we can span the ...
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gazebo is not lunaching moveit package

I have a ros noetic moveit package a robotic arm having demo_gazebo.launch file ...
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2 answers
549 views

Why is admittance control better than impedance control for huma robot collaboration?

I have seen many papers that use admittance control for human robot collaboration but no one tells why admittance is the choice and not impedance. Is it something very trivial that I should know or ...
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Transformation Pose

Hi I am doing a transform from the object to the base_link the orientation seems to be right but the positioning is wrong.Here is my code. i had to change the translation values as when i move foward ...
1 vote
1 answer
76 views

UR robots always have 2 parallel axes. Why not at a singularity?

I thought I understood the Jacobian and singularities pretty well, but then I was asked: UR robots (and others) have 2 joints that are always in parallel. Doesn't this put the robot at a singularity ...
1 vote
1 answer
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Standard Notation/Name for Velocity Transformations

I've been looking to see if there's any standard notation for a matrix to convert an end-effector velocity vector $\xi_n^0 = \begin{bmatrix} v \\ \omega \end{bmatrix}$ from one frame of reference to ...
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4 answers
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DH Parameter for OpenManipulator X from Robotis

I try to solve forward kinematics problem for OpenManipulator X from Robotis by using standard DH convention. The figure and dimension of the robot like this pic I try to find DH parameter and got ...
1 vote
2 answers
221 views

Parallel spatial mechanism - DOF

The parallel mechanism is composed of a moving platform and a base (or frame) connected by four legs. Each leg is composed of five revolute joints numbered 1, 2, … 5 from the base to the moving ...
3 votes
1 answer
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How do I assign the origin of the frames in the Denavit Hartenberg convention?

I am studying the Denavit Hartenberg and to practice I am using the following manipulator: I have been able to assign some of the frames almost correctly, but i did some mistakes I cannot understand. ...
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1 answer
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Where can I find 6 DOF manipulator packages for gazebo?

Hello. Where can I find 6 DOF manipulator with a 4-wheel mobile base packages for gazebo? Thanks. Originally posted by NickRos on ROS Answers with karma: 1 on 2023-02-14 Post score: 0
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1 answer
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How to calculate Exponential coordinates of end_effector from Transformation matrix

I want to know Exponential coordinates of end effector $\text{S}\theta$(6-vector) from end effector transformation matrix. I calculated the transformation matrix of the end effector from the forward ...
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1 answer
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How to add gripper to robot arm and plan according to the end effector on Moveit

Hello! I am simulating for a university project, the Elfin 5 robot arm which package can be found here along with a gripper which package is found here. Being new to Moveit, I am finding trouble to ...
1 vote
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45 views

Grasp matrix implementation

I've majorly followed Dex-net implementation to calculate a grasp matrix (G) to compute other grasp quality metrics (e.g., Ferrari Canny L1 metric or smallest singular value of G). Based on my ...
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1 answer
191 views

Newton-Euler Inverse Dynamics by Screw

I paste this algorithm from textbook Modern Robotics P294 in chapter 8: This is coordinate invariance of Newton-Euler equations. In the textbook, they use the ...
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Meaning of p(q) in the expression for minimum clearance from obstacle for redundant robotic manipulators

Can somebody who has studied Industrial manipulators or has worked on Industrial manipulators using Jacobian Inverse and Jacobian Pseudo inverse algorithm for Inverse Kinematics please explain what ...
1 vote
2 answers
2k views

Why does the Denavit-Hartenberg representation fail to capture the length of the last link in my model?

The length of the last link (1.73) of my model (of a human finger) is not represented in any of the parameters that I calculated using the Denavit-Hartenberg algorithm, which I think can't be right. I ...
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1 answer
186 views

definition of self motion

From my understanding, self motion refers to a set of joint velocities which doesn't cause any cartesian motion on the end-effector. Here, by motion it is meant both linear and angular components or ...
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1 answer
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Design optimization method using indices

There are several methods like manipulability and conditioning index for design optimization kinematics performance, but these methods rely on the singular values of the jacobian matrix. I described ...
2 votes
1 answer
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Redundancy and Null space projection

I'm reading "Theory of Robot Control" by Carlos Canudas Wit, Bruno Siciliano, Georges Bastin. In Task space control chapter, exploiting the redundancy by means of null space as shown below ...
10 votes
4 answers
2k views

Implementing a torque-controlled method on a position-controlled robot

I am working with a position-controlled manipulator. However, I want to implement a torque-controlled method on this robot. Is there any way to convert a torque command to a position command? I try ...
2 votes
2 answers
128 views

Why applied joint torque will affect another joint?

I want to ask a very simple question. For the robot dynamics Newton-Euler algorithm, suppose there is a two-link planar robot, we can write the simple dynamic equation form as $M(\theta)\ddot{\theta} ...
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How to find workspace of parallel manipulator by monte carlo method?

I am working on a 3 DOF parallel manipulator, I was successful in solving the inverse kinematics and forward kinematics of my manipulator. But I am facing a problem in generating a workspace for it. I ...
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2 answers
74 views

Is this motion possible for this manipulator?

I'm currently solving the exercises of Modern Robotics book. I came across this problem but it is not clear to me how to approach it. I computed the analytic Jacobian which is $$ \begin{bmatrix} \dot{...
2 votes
1 answer
193 views

Equations of motion with mass attached to end effector and external force

I have to find the equations of motion for the given manipulator: The links of the manipulator are considered weightless and the equations of motion have to be derived by using the Lagrange equations....
1 vote
2 answers
172 views

How to obtain the Jacobian matrix for this 2Planar without differentiation

Take a look at the below picture, I would like to derive the Jacobian matrix without differentiation. In this Modern Robotics book, the screw theory is used. I've derived the forward kinematic using ...
2 votes
1 answer
161 views

Degrees of Freedom

What is the Degree of Freedom for a k-link planar serial chain for k = 2, 3, 6? Using Grüber Formula, I get k-link chain has k Degrees of Freedom. But the maximum DoF in a plane can be 3. I am not ...
1 vote
1 answer
215 views

Feed-forward controller with lookup table

does anyone have experience in implementing a feed-forward controller for a hydraulic cylinder? Often, when a hydraulic cylinder is controlled with PWM values, people (https://drive.google.com/file/d/...
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1 answer
304 views

How to calculate potential enegy of manipulator?

I'm trying to obtain dynamics of a 4 DOF robot. Firstly, I calculated all Transformation matrices and Jacobians. While solving Lagrangian there is two main things one is kinetic energy and the other ...
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2 answers
254 views

Pose of the end-effector

I am trying to get the pose of the end-effector. I have attached the picture. I am stuck. I wrote the transformation matrices - I am not sure how to move forward next. How do I find the end-effector ...
1 vote
1 answer
98 views

How to calculate holding and operating torque at the base?

Could anyone please help me with the formula to calculate the operating torque and holding torque at the base to rotate the structure on top of it as shown in image with white arrows? Thank you in ...
1 vote
1 answer
99 views

C space for R5 manipulator

Trying to create a collision avoidance model (RRT) for an RRRRR manipulator. I am unable to wrap my head around how to represent the same in configuration space. Anything upto 3 joint variables is ...
7 votes
3 answers
2k views

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

In theory, controlling a 6D pose (3D position + 3D orientation) would require 6 joints, and - assuming the robot is carefully designed - the inverse kinematics should be solvable for that case. Adding ...
4 votes
1 answer
193 views

Why are serial manipulators almost always made of single dof joints?

I am currently taking my first robotics class and I found it curious that all serial manipulators have single dof joints. Why not use joints with more dof and reduce the number of components? Will ...
1 vote
1 answer
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Forward/inverse kinematics and transformation matrices

I have found the homogeneous transformation matrix that can be used to determine the relation between the parent and child links of a robot. This matrix is shown below. $T_i = \left[\begin{array}{ c ...
1 vote
1 answer
111 views

Why is a joint space trajectory unable to deal with operational space obstacles?

I have found several sources that state that a Joint space trajectory model is not capable of dealing with obstacles in the manipulator workspace. These sources include: slide 10 of "Manipulator ...
1 vote
1 answer
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homogenous transformation matrix variants

I am working on some manipulator projects and come across a few variants of the homogenous transformation matrix. I've been working on matlab and they give slightly different answers. Assuming both ...