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The 6-joint industrial robots commonly used in actual production have 6 movable joints (axes), and the definition of the motion axis of different industrial robots is also different. The axis used to ensure that the end effector reaches any position in the workspace is called the basic axis or main axis, and the axis used to achieve any spatial posture of the end effector is called the wrist axis or secondary axis.
1. Common industrial robot body motion axis definition table
First axis: The first axis is the connection position of the chassis, and is also the load-bearing and core position. It bears the weight of the entire robot and the robot's large horizontal swing to the left and right.
Second axis: An important axis that controls the robot's forward and backward swing and extension and retraction.
The third axis: The third axis is also the axis that controls the robot's forward and backward swing, but the swing amplitude is much smaller than that of the second axis. However, this is also the basis for the arm length of the six-axis robot.
The fourth axis: The fourth axis is an axis that controls the 180° free rotation of the upper arm part, which is equivalent to the human forearm.
Fifth axis: The fifth axis is very important. After you have almost adjusted the position, you need to accurately position it on the product, which requires the use of the fifth axis, which is equivalent to the human wrist.
Sixth axis: After you position the fifth axis on the product, if you need to make some minor changes, you will need to use the sixth axis, which is equivalent to a turntable that can rotate 360° horizontally. You can position the product more accurately.
The 6-axis robot ensures that the end effector reaches any position in the workspace through the 1st, 2nd and 3rd basic axes, and realizes any spatial posture of the end effector through the 4th, 5th and 6th axes. 6 axes are required because the 6-degree-of-freedom motion of the end is to be realized.
2. Singularity
Most 6-axis articulated robots, due to mechanical or soft limit limits, will have inverse kinematics with no solution in their motion space, that is, the coordinate-based planned motion cannot be clearly reversed into the rotation angle of each joint axis of the robot. These inverse kinematics points in the robot workspace are called "singular points". Robot singular points can be roughly divided into the following three types.
Shoulder singularity: Shoulder singularity occurs when the center of the robot wrist is in line with the J1 axis joint. This will cause joint axes 1 and 4 to try to rotate 180 degrees instantly.
Elbow singularities: Elbow singularities occur when the center of the robot wrist is in the same plane as joint axes 2 and 3. Elbow singularities look like the robot is "reaching too far", causing the elbow to lock in a certain position in space.
Wrist singularity: This occurs when the robot’s two wrist axes (joint axes 4 and 6) are in a straight line, which can cause these joints to try to rotate 180 degrees at once.
Singularity occurs when a certain point in space cannot be clearly converted into the rotation angle of each joint axis of the robot, resulting in ambiguity.
3. Parallel robot
Parallel robot, also known as Parallel Mechanism, or PM for short, can be defined as a closed-loop mechanism in which a moving platform and a fixed platform are connected by at least two independent motion chains, the mechanism has two or more degrees of freedom, and is driven in parallel.
4.SKU
SKU stands for Stock Keeping Unit, which is the basic unit for measuring inventory in and out, and can be in units of pieces, boxes, pallets, etc. SKU is a necessary method for logistics management of large supermarket chain DC (distribution center). It has now been extended to the abbreviation of product unified number, and each product has a unique SKU number.
5. Flange
The flange in a robot generally refers to the chassis of the robot or the chassis at the joint of the robot.
6. Near Field of View and Far Field of View
The near-end field of view 1000*1170@1.2m means that at a distance of 1.2m from the camera, the horizontal range is 1m and the vertical range is 1.17m. Similarly, the far-end field of view 2910*3360@3.5m means that at a distance of 3.5m from the camera, the horizontal range is 2.91m and the vertical range is 3.36m.
7.Eye-to-Hand 和 Eye-in-Hand
The robot's vision system is divided into a fixed scene vision system and a moving "hand-eye" vision system. The camera and the end of the robot's hand constitute the hand-eye vision system. According to the different relative positions of the camera and the robot, the hand-eye vision system is divided into the Eye-in-Hand system and the Eye-to-Hand system. The camera of the Eye-in-Hand system is installed at the end-effector of the robot's hand and moves with the robot during the robot's work. The camera of the Eye-to-Hand system is installed in a fixed position outside the robot body and does not move with the robot during the robot's work process.
8. Hand-eye calibration
Hand-eye calibration is the position relationship between the robot's hand and eye, that is, the position transformation relationship X between the robot's end joint coordinate system and the camera coordinate system, which can be solved by the equation AX=XB. A represents the transformation relationship between the robot's end joints during two adjacent movements, and B represents the relative movement of the camera coordinates during two adjacent movements. The derivation process is as follows. In the derivation process, we will use four coordinate systems, namely:
●Basic coordinate system (expressed as base)
●Robot coordinate system (expressed by tool)
●Camera coordinate system (denoted by cam)
● Calibration object coordinate system (expressed in cal)
Description of the conversion relationship between coordinate systems:
●baseHtool: represents the transformation relationship from the manipulator coordinate system to the base coordinate system, which can be obtained from the robot system. (known)
●toolHcam: represents the conversion relationship from the camera coordinate system to the robot coordinate system; this conversion relationship remains unchanged during the movement of the robot; (unknown, to be determined)
●calHcam：表示相机坐标系到标定板坐标系的转换关系（相机外參），可以由相机标定求出；（相当于已知）
●baseHcal: represents the transformation from the calibration plate coordinate system to the base coordinate system, which is the final desired result; as long as the relative position of the manipulator and the calibration plate remains unchanged, the transformation matrix does not change.
So: A is known, X is to be determined, and B needs to be known through camera calibration.
After the camera detects the pixel position of the target in the image, the pixel coordinates of the camera are transformed into the spatial coordinate system of the manipulator through the calibrated coordinate transformation matrix X, and then the movement of each motor is calculated according to the manipulator coordinate system, so as to control the manipulator to reach the specified position.
9. Point Cloud
Point cloud is a data set of points in a certain coordinate system. Points contain rich information, including three-dimensional coordinates X, Y, Z, color, classification value, intensity value, time, etc. Point clouds are divided into two types based on their composition characteristics: one is ordered point cloud and the other is disordered point cloud.
10.ROI
ROI: Region of Interest. In machine vision and image processing, the area to be processed is outlined in the image to be processed in the form of a box, circle, ellipse, irregular polygon, etc., which is called the region of interest, ROI.
11. Mask
The concept of mask in digital image processing is borrowed from the process of PCB plate making. In semiconductor manufacturing, many chip process steps use photolithography technology, and the graphic "negative" used in these steps is called a mask (also called a "mask"), which is used to cover an opaque graphic template in a selected area on the silicon wafer, and then the following corrosion or diffusion will only affect the area outside the selected area.
12. Euler Angles
Euler angles are a set of independent angular parameters used to determine the rotation of a rigid body at a fixed point. They are composed of the nutation angle θ, the precession angle (i.e., the precession angle) ψ, and the rotation angle j. They are named after Euler who first proposed them. There are many ways to take them, and the following is a common one. As shown in the figure, a fixed coordinate system Oxyz and a moving coordinate system Ox′y′z′ fixed to the rigid body are made from the fixed point O. The axes Oz and Oz′ are the basic axes, and their perpendicular planes Oxy and Ox′y′ are the basic planes. The angle θ measured from the axis Oz to Oz′ is called the nutation angle. The perpendicular line ON to the plane zOz′ is called the nodal line, which is the intersection of the basic planes Ox′y′ and Oxy. In the right-handed coordinate system, the angle θ should be measured in the counterclockwise direction when viewed from the positive end of ON. The angle ψ measured from the fixed axis Ox to the nodal line ON is called the precession angle; the angle j measured from the nodal line ON to the moving axis Ox′ is called the rotation angle.
13. Margin
Margin refers to the degree of leeway and the tolerance for a certain error. The tolerance margin is determined based on the object and scope of statistics.
14. Region Growing Segmentation Method
Clustering is performed based on the number of check points near the seed point that are included when the region grows.
15. STL Model
STL model is a geometric model that uses a set of triangles to represent the outer contour of an object. In practical applications, there are requirements for STL model data, especially in the RP field where STL models are widely used. STL model data must be tested before use. This test mainly includes two aspects: the validity of STL model data and the closure check of STL model.
16. Rendering
In computer graphics, rendering refers to the process of generating images from software models. It is the last step in CG and the stage that ultimately makes the image conform to the 3D scene.
17.CAD
CAD stands for Management Software Computer Aided Design (MS-CAD), which refers to the process of using computer software to design management software on a graphical development interface, analyzing and generating management software that can be used independently by designing the flow structure, data structure and automatic data loading of the computer software system.
18.RoboDK
RoboDK is a universal robot simulation software that supports offline programming software. Using RoboDK can better debug and plan robot work and avoid errors.
19.PRM
PRM is a graph search-based method that converts continuous space into discrete space and then uses search algorithms such as A* to find paths on the roadmap to improve search efficiency. The PRM method based on random sampling technology can effectively solve path planning problems in high-dimensional space and complex constraints.
20.Teaching pendant
It is a handheld device used for manual operation, programming, parameter configuration and monitoring of robots.
21.OMPL
OMPL (The Open Motion Planning Library) is an open source robot motion planning library (based on C++) based on sampling methods. Most of the algorithms in it are derived from RRT and RPM, such as RRTStar, RRT-Connect, etc.
22. VTK
The Visualization Toolkit (VTK) is an open source, cross-platform graphics application library that supports parallel processing (VTK has been used to process data of nearly 1 Petabyte in size on a large system with 1024 processors owned by the Los Alamos National Laboratory in the United States).
24. Repeatability
Repeatability is the measurement difference that the sensor shows each time the measured quantity changes to a certain measurement point.
25. Tilt-Shift Lens
Tilt-shift lenses are lenses that can achieve tilt and offset functions.
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