10 Robots and handling systems, robot control Flashcards
Robot Definition (ISO 8373/VDI 2860)
- ISO 8373:
‘automatically controlled, reprogrammable multipurpose manipulator. Programmable in three or more axes’ - VDI-Guideline 2860:
Industrial robots are universally applicable manipulators with more than one axis. The movements of these axes are programmable in respect to time sequence, path or rotation angles (i.e. without mechanical influence). If necessary sensors can be applied to guide the robot.
Robots - Areas of Application
- Spot Welding
- Arc Welding
- Handling
- Assembly
- Palletizing
- Painting
- Coating
- Deburring
Types of Robots
- Collaboration Robots
- SCARA (Selective Compliance Robot Arm)
- Portal Robot
Collaboration Robots
o Collaboration means the cooperation of humans and robots on the same component, in the same workspace and at the same time. -> Considerably increases the risk for the worker
o Equipped with additional sensor technology to increase safety for humans
SCARA (Selective Compliance Robot Arm)
o 4 degrees of freedom
o Use: Assmebly, Pick&Place, quality check, packaging
o Advantage: Good motion dynamics, positioning accuracy
o Disadvantage: Low payload and reach
Portal Robot
o Use: Handling in automated production cell
o Advantage: reach, positioning accuracy, base can absorb mechanical stress
4 typical features for the description of performance limits of an industrial robot
Absolute positioning accuracy
Load capacity and moving masses
Range of dynamics
Workspace
Absolute Positioning Accuracy
The accuracy the robot satisfies when moving the tool center point (TCP) under variable constraints (speed, acceleration, payload or temperature) from any direction to any position in the workspace with respect to the stationary cartesian coordinate system.
Repeatability
The accuracy the robot achieves when moving the TCP repeatedly to a defined position under constant constraints (direction of movement, speed, acceleration, payload, temperature). The repeatability is defined by the maximum difference between the reached positions.
Accuracy of Industrial Robots
To measure the absolute accuracy and the the repeatability, a position is commanded, that should be reached. This position is enclosed by defined circles with different diameters.
Transformation - Definition and Goal
Description of an abstraction of a real system
Goal: Transformation of the real robot design to a mathematically equivalent description. -> Model is developed from the real system and then is mathematically described
Definition of the coordinate system
- Joint Coordinates
- Global Coordinates
- Tool Coordinate System
o Necessary for the description of robot movements.
o Joint coordinates: Describe the spatial layout of the robot joints, related to the local, immovable coordinate origin in the axis.
o Global coordinates: Define the position and orientation of the Tool-Center-Point (TCP) in relation to a basic coordinate system of the robot
o Tool coordinate systems: Definition is required for the programming of operation tasks with cartesian coordinates
Forward and inverse transformations
o The actual position of the TCP can be calculated during the movement of the robot through the usage of forward transformation via robot axes positions. -> Forward transformation is an addition of the axes-distance-vectors, starting at the base of the robot up to the TCP
o Is the commanded position of the robot movement determined by Cartesian position and orientation demand, the axes positions of the robot must be calculated with the algorithms of the inverse transformation, according to its kinematics.
Homogeneous Coordinates
o Mathematical form of representation of all important transformations in the three dimensional space in a 4x4 matrix.
o Top left 3x3 matrix shows the three rotations around the X-, Y-, and Z-axis.
o Attached vector shows translation X-, Y- and Z-direction
o Advantage: Opportunity of a standardized presentation of several transformations, by which transformations, performed one after another, can be mathematically linked clearly arranged.
Denavit-Hartenberg Transformation
Mathematical method, that, on the basis of homogeneous matrices and the so called Denavit-Hartenberg-Convention, describes the transformation of position coordinates within kinematic tracks. It supports the calculation of the direct kinematic and is known as a standard method.
