Cartesian coordinate robot

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Kinematic diagram of Cartesian (coordinate) robot Descartes configuration.png
Kinematic diagram of Cartesian (coordinate) robot
A plotter is an implementation of a Cartesian coordinate robot. Hp 9862a.jpg
A plotter is an implementation of a Cartesian coordinate robot.

A Cartesian coordinate robot (also called linear robot) is an industrial robot whose three principal axes of control are linear (i.e. they move in a straight line rather than rotate) and are at right angles to each other. [1] The three sliding joints correspond to moving the wrist up-down, in-out, back-forth. Among other advantages, this mechanical arrangement simplifies the robot control arm solution. It has high reliability and precision when operating in three-dimensional space. [2] As a robot coordinate system, it is also effective for horizontal travel and for stacking bins. [3]

Contents

Configurations

Linear stage Zaber motorized linear stage.jpg
Linear stage
Gantry robot Robot Portico tecno-840.jpg
Gantry robot

Robots have mechanisms consisting of rigid links connected together by joints with either linear (prismatic P) or rotary (revolute R) motion, or combinations of the two. [4] [5]  Active prismatic P and active revolute R joints are driven by motors under programmable control to manipulate objects to perform complex automated tasks. The linear motion of active prismatic P joints may be driven by rotary motors through gears or pulleys. Cartesian coordinate robots are controlled by mutually perpendicular active prismatic P joints that are aligned with the X, Y, Z axes of a Cartesian coordinate system. [6] [7]  Although not strictly ‘robots’, other types of manipulators, such as computer numerically controlled (CNC) machines, 3D printers or pen plotters, also have the same mechanical arrangement of mutually perpendicular active prismatic P joints.

Joint topology

A single chain of links and joints connects a moving object to a base of serial manipulators. Multiple chains (limbs) connect the moving object to the base of parallel manipulators. [8]   Most Cartesian coordinate robots are fully serial or a combination of serial and parallel connected linkages.  However, there are some Cartesian coordinate robots that are fully parallel-connected. [9] [10] [11]

Degrees of freedom

Since they are driven by linear active prismatic P joints, Cartesian coordinate robots typically manipulate objects with only linear translation T degrees of freedom.  However, some Cartesian coordinate robots also have rotational R degrees of freedom. [12]

Construction

Each axis of a Cartesian coordinate robot typically is a linear stage consisting of a linear actuator geometrically parallel with linear bearings. The linear actuator is typically between two linear bearings spaced apart from each other to support moment loads.  Two perpendicular linear stages stacked on top of each other form an XY table.  Examples of XY tables include the XY axes of milling machines or precision positioning stages. At least one of the linear stages of cantilevered Cartesian coordinate robots is supported at only one end. Cantilevered construction provides accessibility to parts for pick-and-place applications such as laboratory automation for example. Cartesian coordinate robots with the horizontal member supported at both ends are sometimes called gantry robots; mechanically, they resemble gantry cranes, although the latter are not generally robots. Gantry robots are often quite large and may support heavy loads.

Applications

Popular applications for Cartesian coordinate robots are computer numerical control machines (CNC machine) and 3D printing. The simplest application is used in milling machines and plotters where a tool such as a router or pen translates across an X-Y plane and is raised and lowered onto a surface to create a precise design.

Pick and place machines are another application for Cartesian coordinate robots.  For example, overhead gantry Cartesian robots are applied for continuous parts loading and unloading on CNC lathes production lines, performing 3-axis (X, Y, Z) pick and place operations of heavy loads with high speed performance and high positioning accuracy.  In general, overhead gantry Cartesian robots are suitable for many automation systems. [13]

See also

Related Research Articles

<span class="mw-page-title-main">Cartesian coordinate system</span> Most common coordinate system (geometry)

In geometry, a Cartesian coordinate system in a plane is a coordinate system that specifies each point uniquely by a pair of real numbers called coordinates, which are the signed distances to the point from two fixed perpendicular oriented lines, called coordinate lines, coordinate axes or just axes of the system. The point where they meet is called the origin and has (0, 0) as coordinates.

<span class="mw-page-title-main">Machine</span> Powered mechanical device

A machine is a physical system that uses power to apply forces and control movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to natural biological macromolecules, such as molecular machines. Machines can be driven by animals and people, by natural forces such as wind and water, and by chemical, thermal, or electrical power, and include a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement. They can also include computers and sensors that monitor performance and plan movement, often called mechanical systems.

<span class="mw-page-title-main">Industrial robot</span> Robot used in manufacturing

An industrial robot is a robot system used for manufacturing. Industrial robots are automated, programmable and capable of movement on three or more axes.

<span class="mw-page-title-main">Stewart platform</span> Type of parallel manipulator

A Stewart platform is a type of parallel manipulator that has six prismatic actuators, commonly hydraulic jacks or electric linear actuators, attached in pairs to three positions on the platform's baseplate, crossing over to three mounting points on a top plate. All 12 connections are made via universal joints. Devices placed on the top plate can be moved in the six degrees of freedom in which it is possible for a freely-suspended body to move: three linear movements x, y, z, and the three rotations.

<span class="mw-page-title-main">Numerical control</span> Computer control of machine tools

In machining, numerical control, also called computer numerical control (CNC), is the automated control of tools by means of a computer. It is used to operate tools such as drills, lathes, mills, grinders, routers and 3D printers. CNC transforms a piece of material into a specified shape by following coded programmed instructions and without a manual operator directly controlling the machining operation.

<span class="mw-page-title-main">Robot kinematics</span> Geometric analysis of multi-DoF kinematic chains that model a robot

In robotics, robot kinematics applies geometry to the study of the movement of multi-degree of freedom kinematic chains that form the structure of robotic systems. The emphasis on geometry means that the links of the robot are modeled as rigid bodies and its joints are assumed to provide pure rotation or translation.

<span class="mw-page-title-main">FANUC</span> Japanese robotics company

FANUC is a Japanese group of companies that provide automation products and services such as robotics and computer numerical control wireless systems. These companies are principally FANUC Corporation of Japan, Fanuc America Corporation of Rochester Hills, Michigan, USA, and FANUC Europe Corporation S.A. of Luxembourg.

<span class="mw-page-title-main">Linkage (mechanical)</span> Assembly of systems connected to manage forces and movement

A mechanical linkage is an assembly of systems connected so as to manage forces and movement. The movement of a body, or link, is studied using geometry so the link is considered to be rigid. The connections between links are modeled as providing ideal movement, pure rotation or sliding for example, and are called joints. A linkage modeled as a network of rigid links and ideal joints is called a kinematic chain.

<span class="mw-page-title-main">Articulated robot</span>

An articulated robot is a robot with rotary joints. Articulated robots can range from simple two-jointed structures to systems with 10 or more interacting joints and materials. They are powered by a variety of means, including electric motors.

<span class="mw-page-title-main">SCARA</span> Type of industrial robotic arm

The SCARA is a type of industrial robot. The acronym stands for Selective Compliance Assembly Robot Arm or Selective Compliance Articulated Robot Arm.

<span class="mw-page-title-main">Serial manipulator</span>

Serial manipulators are the most common industrial robots and they are designed as a series of links connected by motor-actuated joints that extend from a base to an end-effector. Often they have an anthropomorphic arm structure described as having a "shoulder", an "elbow", and a "wrist".

<span class="mw-page-title-main">Parallel manipulator</span> Type of mechanical system

A parallel manipulator is a mechanical system that uses several computer-controlled serial chains to support a single platform, or end-effector. Perhaps, the best known parallel manipulator is formed from six linear actuators that support a movable base for devices such as flight simulators. This device is called a Stewart platform or the Gough-Stewart platform in recognition of the engineers who first designed and used them.

In classical mechanics, a kinematic pair is a connection between two physical objects that imposes constraints on their relative movement (kinematics). German engineer Franz Reuleaux introduced the kinematic pair as a new approach to the study of machines that provided an advance over the notion of elements consisting of simple machines.

<span class="mw-page-title-main">Robotic arm</span> Type of mechanical arm with similar functions to a human arm.

A robotic arm is a type of mechanical arm, usually programmable, with similar functions to a human arm; the arm may be the sum total of the mechanism or may be part of a more complex robot. The links of such a manipulator are connected by joints allowing either rotational motion or translational (linear) displacement. The links of the manipulator can be considered to form a kinematic chain. The terminus of the kinematic chain of the manipulator is called the end effector and it is analogous to the human hand. However, the term "robotic hand" as a synonym of the robotic arm is often proscribed.

There are many conventions used in the robotics research field. This article summarises these conventions.

<span class="mw-page-title-main">Denavit–Hartenberg parameters</span> Convention for attaching reference frames to links of a kinematic chain

In mechanical engineering, the Denavit–Hartenberg parameters are the four parameters associated with a particular convention for attaching reference frames to the links of a spatial kinematic chain, or robot manipulator.

<span class="mw-page-title-main">X-Y table</span>

X-Y tables, also known as cross working tables or coordinate tables, help provide horizontal motion for automated machinery such as assembly robots in manufacturing facilities. Robotic arms and other automated machinery have only a limited range of motion while their bases remain stationary; X-Y tables allow this basis to move horizontally along X and Y axis. Also known as XY stages, XY tables are motorized linear slides with linear motion based in bearings which are driven by a drive mechanism, typically a linear motor. XY tables are built and configured to provide high-performance positioning along multiple axes.

The product of exponentials (POE) method is a robotics convention for mapping the links of a spatial kinematic chain. It is an alternative to Denavit–Hartenberg parameterization. While the latter method uses the minimal number of parameters to represent joint motions, the former method has a number of advantages: uniform treatment of prismatic and revolute joints, definition of only two reference frames, and an easy geometric interpretation from the use of screw axes for each joint.

<span class="mw-page-title-main">High performance positioning system</span> Industrial Engineering method

A high performance positioning system (HPPS) is a type of positioning system consisting of a piece of electromechanics equipment (e.g. an assembly of linear stages and rotary stages) that is capable of moving an object in a three-dimensional space within a work envelope. Positioning could be done point to point or along a desired path of motion. Position is typically defined in six degrees of freedom, including linear, in an x,y,z cartesian coordinate system, and angular orientation of yaw, pitch, roll. HPPS are used in many manufacturing processes to move an object (tool or part) smoothly and accurately in six degrees of freedom, along a desired path, at a desired orientation, with high acceleration, high deceleration, high velocity and low settling time. It is designed to quickly stop its motion and accurately place the moving object at its desired final position and orientation with minimal jittering.

In robotics, Cartesian parallel manipulators are manipulators that move a platform using parallel-connected kinematic linkages ('limbs') lined up with a Cartesian coordinate system. Multiple limbs connect the moving platform to a base. Each limb is driven by a linear actuator and the linear actuators are mutually perpendicular. The term 'parallel' here refers to the way that the kinematic linkages are put together, it does not connote geometrically parallel; i.e., equidistant lines.

References

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