Image Credit: Machine Design
The subject of discussion: Cartesian Robot Facts and Features
- What is a Cartesian Robot? | Cartesian Robot System
- Cartesian Robot Design | Cartesian Coordinate Robot
- Cartesian Robot Controls
- Cartesian Robot Work Envelope
- Cartesian Robot Example
- Cartesian Robot Kinematics
- Cartesian Robot Applications
- Cartesian Robot Advantages
- Cartesian Robot Disadvantages
- Differences between Cartesian, Six-Axis, and SCARA Robots
What is a Cartesian Robot? | Cartesian Robot System
Cartesian Robot Definition
A Cartesian Robot or a cartesian coordinate robot (also known as a linear robot) is an industrial robot with three primary control axes that are all linear (meaning that they travel along a straight line rather than rotating) and mutually perpendicular to one another. The 3- sliding joints allow you to move your wrist up-down, in-and-out, and back-forth. In 3D-space, it is incredibly dependable and precise. It’s also useful for horizontal movement and piling bins as a robot coordinate system.
Cartesian Robot Design | Cartesian Coordinate Robot
Cartesian Robot Configurations
To understand the design mechanism of a Cartesian Robot, one of the first things that need to be understood is the concept of Joint Topology. A moving target is bound to a base of serial manipulators by a continuous chain of links and joints. The moving target is connected to the bottom of parallel manipulators by several chains (limbs). The majority of Cartesian coordinate robots use a mix of serial and parallel related linkages. Any Cartesian coordinate robots, on the other hand, are totally parallel-connected.
Next comes into the picture is the degree of freedom. Cartesian coordinate robots commonly manipulate structures with only linear translation T degrees of freedom since linear working prismatic P joints operate them. On the other hand, few Cartesian coordinate robots have rotational R degrees of freedom as well.
The layout of the axes is one of the first things to determine when constructing a Cartesian robot, not only to accomplish the necessary motions but also to ensure the device has adequate rigidity, which can affect load-carrying capability, travel precision, and positioning accuracy.
Some applications that need Cartesian coordinate movement are well assisted by a gantry robot than by a Cartesian method, mainly if the Y-axis involves a longstroke or if the Cartesian procedure will place a substantial moments at axes. A gantry device with Dual-X or dual-Y axes can be needed to avoid unnecessary deflection or vibration in these situations.
A linear level, consisting of a linear actuator geometrically parallel with linear bearings, is usually used for each axis of a Cartesian coordinate robot and the linear actuator is usually mounted between 2 linear bearing that are set apart to back moment load. An XY table is made up of two perpendicular linear stages stacked on top of each other.
Cartesian Industrial Robots | Pick and Place Cartesian Robot | Gantry Cartesian Robot
Pick-and-place application, such as laboratory use, benefit from cantilevered construction because components are easily accessible. Gantry robots are Cartesian coordinate robots with horizontal members supported at both ends; physically, they are similar to gantry cranes, which are not necessarily robots. Gantry robots are often gigantic and capable of carrying heavy loads.
Difference between Gantry and Cartesian robots
A Cartesian robot has one linear actuator on each axis, whereas, a gantry robot has two bases (X) axes and a second (Y) axis that spans them. This design stops the 2nd axis from being cantilevered (more on that later) and makes for even longer stroke lengths in gantries and greater payload compare to Cartesian robot.
The most-common of Cartesian-robots use the dual guided design because it provides more excellent protection for overhung (moment) loads; however, axes with dual linear guides have a more foot print than axes with single one, in comparison dual-guide systems generally short (in the vertical direction) and may eliminate interaction with other areas of the machine. The argument is that the sort of axes you chose has an impact not just on the Cartesian system’s efficiency but also on the overall footprint.
Cartesian Robot Actuators
If a Cartesian mechanism is the best choice, the following design factor usually is the actuator control unit, which may be a bolt, screw, or pneumatic-driven system. Linear actuators are generally available with a single or dual linear guide depending on the drive system.
Cable Control and Management
Cable control is another essential feature of this robot design that is often ignored in the early stages (or merely postponed to later stages of the plan). For control, air (for pneumatic axes), encoder input (for servo-driven Cartesian), sensor, and other electrical apparatuses, each axis involves several cables.
When systems and components are connected through the Industrial Internet of Things (IIoT), the methods and tools used to link them become much more critical and both of these tubes, wires, and connectors must be routed appropriately and maintained to avoid premature fatigue from undue flexing or disruption from interference with other device components.
The type and quantity of cables required, as well as the sophistication of cable management, are all determined by the kind of control and network protocol. Note that the cable management system’s cable carrier, trays, or housings will affect the total system’s measurements, so make sure there’s no conflict with the cabling system and the rest of the robotic components.
Cartesian Robot Controls
Cartesian robots are the preferred method for making point-to-point movements, but they can also do complex interpolated and contoured motion. The type of motion needed will specify the best control device, networking protocol, HMI, and other motion components for the system.
While these components are located independently from the robot’s axes, for the most part, they will have an impact on the motors, wires, and other on-axis electrical components needed. These on-axis elements would influence the first two design considerations, positioning and cable control.
As a result, the design process falls full circle, stressing the importance of constructing a Cartesian robot as an interconnected electromechanical device rather than a set of mechanical parts attached to electrical hardware and software.
Cartesian Robot Work Envelope
Various robot configurations produce distinct working envelope shapes. This working envelope is crucial when choosing a Robot for a specific application because it specifies the manipulator and end effector’s work area. For a multitude of purposes, care should be practiced when studying a Robot’s work envelope:
- The working envelope is the amount of work that can be approach by a point at the end of the Robotic arm, which is typically the middle of the end-effectors mounting arrangments. It does not have any instruments or workpieces owned by the end-effector.
- There are sometimes locations inside the operating envelope that the Robot arm cannot enter. Dead zones are the name given to specific regions.
- The maximum payload capability cited is only achievable at such arm lengths, which may or may not reach maximum reach.
The Cartesian configuration’s operating envelope is a rectangular prism. Inside the working envelope, there are no dead zones, and the Robot can manipulate the full payload over the entire working volume.
Cartesian Robots Examples
A Calculator Plotter
3-axis Cartesian Robot for Dispensing Fruit Fly Food
Cartesian Robot Kinematics
The Cartesian Robot is essentially a three prismatic joint or a PPP Robot. It follows the general rule of determining the forward and inverse kinematics of a serial link robot manipulator, which can be found here.
What is a Cartesian Robot used for? | Cartesian Robot Applications
Computer numerical control machines (CNC machines) and 3D printing are two typical applications for Cartesian coordinate robots. Milling machines and plotters use the most straightforward application, in which a tool, such as a router or a pen moves around an X-Y plane and is lifted and lowered onto a surface to produce a specific pattern.
Cartesian coordinate robotics can also be used in pick-and-place machines. Overhead gantry Cartesian-robots, for example, are used to load and unload components used in CNC lathe line, working in three axis (X, Y, Z) pick and place operation of heavy loads at high-speed and with high precision.
Cartesian Robot Advantages
- They can move heavy payloads due to their compact construction and straight-line travel.
- A single controller can control many robots, obviating the need for PLC solutions or IO between several controllers.
- They can carry heavy loads over long distances because they have long strokes of around 2 meters.
- Their actions and roles are exact and repeatable.
- Cycle times are shortened due to their rapid moving speed and acceleration.
- The option to set 2-units on the Z-axis and minimizes mounting space.
- It can be built with virtually any linear actuator and several drive mechanisms (together with belt, lead-screw, actuator, or linear-motor).
- This mechanical structure simplified the Robot control arm solution, among other things and if working in 3D space, it is highly dependable and precise.
Cartesian Robot Disadvantages
- On the other hand, Cartesian robots have drawbacks such as requiring a vast amount of space to run and being unable to work underwater.
- When operating in a dangerous environment, these robots also need special protection. Another downside of this robot type is that it is usually slower than the others.
- When the air is dirty, it is often difficult to keep dirt out of the sliding components.
- The use of an overhead crane or other material handling equipment to access the work envelope may be prohibited, and repair may be complicated.
Differences between Cartesian, Six-Axis, and SCARA Robots
Cartesian Robot’s Load
The load capacity of a robot (as specified by the manufacturer’s ) required to be greater than the total payload’s weight at the end of the robotic arm with tooling parts. SCARA and six-axis robots are constrained because they carry loads on extended components.
For example, a machining center that manufactures bearing assemblies weighing 100 kg or more. Except for the largest SCARA or six-axis robots, the payload exceeds their capabilities. A traditional Cartesian-robot, on the other hand, can easily pick and position those loads because its support frame and bearings support the whole range of motion.
Cartesian Robot’s Orientation
The robot’s direction is determined by how it is positioned and how it places the pieces or items being pushed. If the floor or line-mounted pedestal of a SCARA or six-axis robot causes an obstacle, such robots may not be the right choice. Small-frame Cartesian robots may be placed overhead and out of the way if the application only involves rotation in a few axes.
However, for complex component handling or function involving four or more axes of motion, a Cartesian robot’s structure may be too obstructive, and a compact SCARA robot, which may be as small as 200 mm2 and four bolts on a pedestal, maybe a better fit.
Cartesian Robot’s Speed
Robot-manufacturer catalogs also have speed ratings in addition to load ratings. Acceleration times over long distances are critical to remember when picking robots for pick-and-place applications. Cartesian-robots can reach five m/sec or higher speeds, rivaling SCARA and six-axis robots.
Cartesian Robot’s Duty Cycle
This is the time it takes to complete a single operating loop. Robots that constantly run 24 hours a day, seven days a week (as in high-throughput scanning and pharmaceutical manufacturing) hit the end of their useful lives faster than those that run for eight hours five days a week. To stop potential aggravation, fix these problems ahead of time and buy robots with long lubrication periods and low maintenance requirements.
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