When designing an automation project involving moving objects or repetitive motion functions, the addition of robots can greatly benefit the project. Choosing the right robot type can reduce design costs and increase the success rate. Simple applications use only a set of repetitive, unchanging programmed motions, while adding a machine vision system or a set of field sensors connected to the robot's control system can enable the robot to achieve adaptive motion, which can change the robot's actual motion positioning.
Robot suppliers can help users select systems with positioning capabilities. Many videos online showcase various robotic systems in motion; when watching these videos, remember: if the video originates from the manufacturer, the robot is typically operating at its performance limits. However, in real-world use, it's impossible for a robot to continue operating at its performance limits.
Many robot manufacturers offer modeling and simulation software to help customers select the robot that best meets their needs. "LOSTPED" helps define the information needed to develop robot parameters; load, tendency, speed, operation, accuracy, environment, and task cycle are the data points required for the proper planning and design of robot systems or any motion control application.
Among the several common robot types available to customers, each robot has some additional features that can be customized to meet customer requirements.
Multi-joint robot
When most people think of industrial robots, they picture a multi-jointed robot. This type of robot often appears in television commercials and industry-related videos. There's no strict definition of a multi-jointed robot; it's generally described as having a fixed base and 4-6 joints. However, jointed robots with as few as 2 axes and as many as 10 axes also exist. Furthermore, end-effector tools (EOATs) can provide even more motion options. A standard characteristic of multi-jointed robots is their ability to work in three-dimensional space or a workspace. The largest workspace of a multi-jointed robot resembles a sphere, and points in space are typically defined using polar coordinates.
Because of their large working range, articulated robots can place end-effectors at virtually any angle on an almost infinite number of planes, making them extremely versatile. For example, in welding, articulated robots offer greater continuity and repeatability than human welders using any welding technique. When the workpiece is in a fixed position, the welding nozzle can precisely position itself at the optimal distance, angle, and speed. Even if the workpiece is not perpendicular to the robot's base, the robot can perform precise and repeatable inspection using 3D lasers and machine vision. Other applications of articulated robots include painting, drilling, tapping, cutting, pick-and-place, material handling, packaging, and assembly.
Among the robot types discussed in this article, articulated robots are the most expensive. Simple movements of articulated robots can usually be programmed by directly teaching the key points and actions, while complex positioning requires writing code for the controller. Field personnel can then modify or fine-tune the robot's position.
SCARA robot
The Selective Compliant Assembly Robotic Arm (SCARA) has a stable base in a fixed position. Its robotic arm is fixed on the z-axis while rotating on the x and y axes. An additional x and y axis joint is located in the middle of the arm. A linear actuator at the end of the arm allows the z-axis to move at a 90-degree angle to the base plane. This linear actuator also has an additional θ-axis, giving the SCARA robot a total of four axes. In many ways, the SCARA robot mimics the movement of a human arm, and its maximum workspace is equivalent to a portion of a cylinder.
During operation, SCARA robotic arms can maintain high-precision positioning while operating at high speeds. If the operating planes are parallel, material handling and product assembly can typically be accomplished using SCARA robotic arms. Using a displacement laser at the tool end enables high-speed three-dimensional coordinate measuring machine (CMM) functions on assembly lines. SCARA robots equipped with machine vision systems can perform precise non-contact inspections. Mounting lasers, plasma cutters, and routers at the tool end of the robotic arm enables precise etching, cutting, and milling operations.
The weight of objects carried by a SCARA robot will generate radial loads on its rotating joints, so its bearings must be strong enough to function properly for the robot's intended lifespan. The momentum of the load on a SCARA robot must not be so high as to slow down the motors or stop the arm from moving.
Cartesian coordinate robot
Cartesian robots can typically handle heavier loads than articulated or SCARA robots at a lower cost. Cartesian robots utilize a frame structure to distribute the load weight (Figure 3). They move linearly along the x, y, and z axes, confined to a frame, which can range in length from hundreds to thousands of meters or feet. The frame can be standard or semi-standard linear guides and ball screws, allowing the robot to be repurposed as needed. The workspace of a Cartesian robot is similar to a rectangle, and it uses a Cartesian coordinate system for positioning.
Cartesian coordinate robots are commonly used for picking up and placing products, as well as for applying sealants, controlling routers, lasers, and plasma cutters, or any movement suitable for a robot's workspace.
Delta Robots
The Delta robot has three parallel arms and rotary or linear actuators. When a force is applied to the actuators, the end effector moves along the x, y, and z axes but does not rotate. The Delta robot was originally designed for handling light loads, but its other applications include 3D printing, surgery, and assembly operations. The Delta robot uses lightweight arms with low inertia, allowing for very fast movement. Unlike robotic arms, the Delta robot can move in a 360-degree circle within its workspace.
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