This article takes an in depth look at industrial robots.
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An industrial robot is an autonomous system of sensors, controllers, and actuators that executes specific functions and operations in a manufacturing or processing line. They operate continuously through repetitive movement cycles as instructed by a set of commands called a program. These machines minimize or eliminate the human factor to gain various advantages in processing speed, capacity, and quality.
Traditional industrial robots must not be confused with a newer robotic technology called collaborative robots. Collaborative robots, or cobots, are designed to work simultaneously and closely with a human operator. They are much smaller but are more versatile. They are equipped with sophisticated sensors that allow them to perceive the actions of nearby personnel.
The main structure of an industrial robot is the arm. The arm is a structure made of links and joints. Links are rigid components that move through space in the range of the robot. The joints, on the other hand, are a mechanical part that connects two links while allowing translational (prismatic) or rotational (revolute) movement. The configuration of these two components classifies the different types of industrial robots.
The most important part of the robot is the end-of-arm-tool (EOAT) or end effector. The EOAT is the component that manipulates the product or process by moving or orienting. They are used to perform special operations such as welding, measuring, marking, drilling, cutting, painting, cleaning, and so on.
In adopting an industrial robotic solution, a process owner may opt to acquire the services of either a manufacturer or an integrator. An industrial robotics manufacturer supplies robots that are made by their own company. They are commonly referred to as original equipment manufacturers (OEM). Since they are responsible for the design and manufacture of the robot, they can expertly provide insights on the installation, operation, and maintenance of the machine.
An industrial robot integrator supplies robotic systems that are made by an OEM. They only perform installation and maintenance services, not the actual production of the machine. They have a wider array of solutions since they can offer more products. They can represent more than one company for each robot component category.
This chapter discusses the advantages of adopting industrial robots in a manufacturing system. Despite the higher investment and capital cost, several economic and intangible benefits can be gained. Because of their efficient operation, industrial robots are worth investing in and can earn back their value in 2 to 5 years.
Higher production rate is the number one reason for investing in an industrial robot system. Robots do not experience fatigue, nor slow down after continuous operation. When designed, operated, and maintained properly, they can efficiently reduce production times. Their processing speed is much faster than humans. This allows them to perform a calculated, quick series of movements, regardless of the complexity.
Industrial robots have actuators that are several magnitudes stronger than their human counterparts. Their actuators rely on the pressure created from hydraulic and pneumatic systems, and electromagnetic forces exhibited by different types of electric drives and motors. Industrial robots also utilize the mechanical advantage brought by specifically designed arm configurations which, in their basic form, are only simple machines. All of these factors allow robots to easily and efficiently lift heavy weights that are far from the capabilities of manual labor.
Common workplace hazards include extreme temperatures, high pressures, toxic materials, heavy loads, fast movements, and high-speed rotations. Industrial robots are useful in operations involving these hazards to eliminate the risk of injury or even fatality. They are expendable and can better withstand harmful working conditions. They can also be repaired if the damage is sustained. Moreover, robots improve workplace safety since they do not make mistakes or cause accidents due to poor judgment unlike human operators. But this is only true if the robot is well designed and programmed.
Less wasted raw material and fewer manpower costs are some of the economic benefits offered by industrial robots. These are operating savings in addition to the higher profit incurred by the better product quality and faster production rate. Efficient use and handling of raw materials are due to the accurate and precise operation of robotic systems. This further leads to lower product rejection rates. In terms of manpower costs, operations employing manual labor are usually more expensive for the same volume of work. There are many miscellaneous costs associated with manual labor such as government-mandated benefits, living allowances, and training.
In a robotic system, its manner of doing work is consistent despite running after hundreds or thousands of cycles. Without human intervention or change in their programming, robots can efficiently execute the same sequence of operations repeatedly and precisely. Its movement patterns, range of motion, the force exerted, speed, and other operating parameters are minimally affected by external factors. This leads to constant and predictable product quality and operating rates.
Robotic systems inherently have higher operating accuracy than human operators. They can easily perform the exact actions intended by their program. This characteristic is important in manufacturing processes that require tight tolerances such as automotive and aircraft parts production. The accuracy of robotic systems is improved by mounting sensors, which allow the machine to perceive and analyze its work envelope. As the sensors‘ level of sophistication is increased, the accuracy of the robot improves.
Today, industrial robots are the equipment behind every precision engineering and manufacturing process. This is attributed to both repeatability and accuracy. These characteristics allow the robot to produce products with consistent properties that are free from errors caused by common mistakes and subjective judgment. Robots can also be fitted with the right set of tools to perform the work properly and smoothly without causing damage to the finished product.
Because of their higher load capacities, faster throughput, and integrated system of tools, industrial robots effectively save space. There is no need for additional equipment to aid human operators in performing their job. Production through manual labor typically requires a larger space for accommodating several workstations to increase the manufacturing line‘s throughput. The same can be achieved by a single industrial robot.
The most common application of industrial robots involves simple pick and place operations., However, with the introduction of better control technologies, powerful actuators, and more sophisticated sensors, industrial robots are also employed in more versatile and critical functions. Below are some of the most common applications of industrial robots.
Industrial robots are widely used as assembly machines. They are suitable for highly repetitive but precise tasks that are tedious for a human operator. Their EOAT is usually mechanical grippers that pick, place, and orient small or large parts in quick succession. Sensors are optional and are typically used for recalibrating the accuracy of the robot‘s movements.
Conventional machining processes include milling, drilling, and turning. Machining typically uses rotary cutters for removing material from a workpiece. When done manually, it involves slowly advancing the rotary cutter to the workpiece. The workpiece can also be advanced by moving it across the table of the machine. The direction and extent of the cut made through the manual process are limited due to the restricted movement and control of the machine. When industrial robots are employed, the rotary cutter is installed on the robot as its EOAT. Using robots as manipulators of the cutting tool allows better control of all cutting parameters such as cutter speed, depth, pressure, and feed rate.
Common non-conventional methods of machining include waterjet cutting, laser cutting, abrasive jet machining, electric discharge machining (EDM), and plasma cutting. These are non-contact machining processes that perform material removal by using highly concentrated streams of water, light, electric charge, or another physical entity. The concentrated stream erodes, vaporizes, or melts the material. High amounts of energy are involved in these processes; this can potentially damage the product or the machine itself if not controlled properly. To accurately control the cutting path of the machine, industrial robots are used. The right cutting speed, stream stability, and accurate control of machine parameters such as power, pressure, and flow rate are properly maintained using digital control.
Palletizing is the process of combining several individual products into a single load for more efficient product handling, storage, and distribution. Depalletizing, on the other hand, is the opposite; it‘s the disassembly of a palletized load. Both of these processes are labor-intensive and can quickly become process bottlenecks. Robotic palletizers are used for their better product handling and cost-efficiency. EOATs integrated into robotic palletizers are mechanical, pneumatic, and magnetic grippers that operate by picking, orienting, and stacking items, similar to the operation of assembly machines.
Robotic welding machines are commonly seen in automotive manufacturing plants, but they are also widely used in many high-volume metal fabrication processes. Increased market competitiveness created the need for better product quality and higher operating rates. This, in turn, requires more accurate and precise welding processes. The main advantage of using industrial robots in welding is better control of different parameters such as current, voltage, arc length, filler feed rate, weld rate, and arc travel speed.
Painting and coating is a sensitive operation that requires highly accurate and repeatable movements to create a layer with uniform thickness. On top of the required accuracy and precision, painting involves working with potentially hazardous chemicals. Many pigments and solvents are poisonous, and some can even create an explosive atmosphere. All these hazards are mitigated by using industrial robots.
Grinding, polishing, and buffing are common secondary fabrication processes used for improving the final appearance and surface properties of the product. These processes involve repetitive, oscillating motions of the abrasive or polishing material. This simple movement of the tool can easily be mimicked by a robotic arm.
Deburring is another secondary process used for removing unwanted material from the final product. Unlike grinding, polishing, and buffing, deburring is done in targeted locations such as edges of cuts from primary machining processes. Hence, deburring requires greater accuracy and precision to prevent damaging the final product.
Machine loading and unloading take advantage of the high load capacity and mechanical advantage offered by robotic systems. Specific machine loading and unloading applications include transferring large metal or plastic parts from casting, molding, and forging processes to conveyor systems or secondary processing stations.
Robotic inspection machines use measuring devices such as optical sensors, proximity sensors, force transducers, and ultrasonic probes. These machines are typically used to precisely measure the dimensions of a product for maintaining quality and consistency. Other inspection applications include non-destructive testing (NDT) of welds wherein ultrasonic probes or arrays are automatically moved and controlled by a robotic system.
Sorting processes utilize the simple pick and place capability and high-speed monitoring of robotic systems. Visual sensors detect variations in size, color, or shape. Upon detection of an odd item, a robot is used to pick and reject the item. Common industries using robotic sorting systems are pharmaceuticals and electronics.
Industrial robots are classified according to their arm configuration. A robotic arm is composed of links and joints. Varying the number and type of these two components yields robots with different configurations. Below are the six types of industrial robots.
A Cartesian robot is composed of three prismatic joints. Thus, the tool is limited to linear motion. The name Cartesian is derived from the three-dimensional Cartesian coordinate system, which consists of X, Y, and Z axes. Cartesian robots are the simplest robotic system since their operation only involves translational movements. This is suitable for applications that only require movement at right angles without the need for orienting the load. Moreover, since one or two of its prismatic joints are usually supported at both ends, they are built to handle heavier loads than other robot types. An example of a Cartesian robot is a gantry machine. Gantry machines, also known as gantry cranes, are used for picking and placing large loads such as palletized loads.
Polar robots, also known as spherical robots, use the three-dimensional polar coordinate system r, θ, and φ coordinate. Instead of having a work envelope in the shape of a rectangular prism, polar robots have a spherical range. Their range of motion has a radius equal to the length of the link connecting the EOAT and the nearest revolute joint. This configuration allows polar robots to have the farthest reach for a given arm length when compared to other robot types. The range of a polar robot can be further extended using a second link connected by a prismatic joint. Because of their wide reach, polar robots are commonly used in machine loading applications.
As the name suggests, a cylindrical robot has a cylindrical range of motion. This type consists of one revolute joint and two prismatic joints. The revolute joint is located at the base of the arm; this allows the rotation of the links about the robot‘s axis. The two prismatic joints are used for adjusting the radius and height of the robot‘s cylindrical work envelope. In compact designs, the prismatic joint used for adjusting the arm‘s radius is eliminated. This one revolute, one prismatic joint configuration is useful in simple pick and place operations where the product feed is located only in one place.
A SCARA is a type of robot that has an arm that is compliant or flexible in the horizontal or XY-plane but is rigid in the vertical direction or Z-axis. Its translational movement on a single plane describes its "Selective Compliant" characteristic. A SCARA has two links, two revolute joints, and a single prismatic joint. The links and the base are connected by the revolute joints oriented at the same axis. The prismatic joint is only for raising or lowering the EOAT. The resulting work envelope of a SCARA is a torus. Its application is similar to that of a cylindrical robot.
A delta robot consists of at least three links connected to an EOAT and a common base. The EOAT is connected to the links by three undriven universal joints. The base, on the other hand, is connected by either three prismatic or three revolute-driven joints. The driven joints work together to allow the EOAT to have four degrees of freedom. For designs using prismatic joints, a fourth link or shaft is usually connected to the EOAT to enable rotation. The EOAT of a delta robot can move along all Cartesian axes and can also rotate around the vertical axis. This results in a dome-shaped work envelope. The simultaneous action of the three driven joints makes delta robots suitable for high-speed pick and place applications.
Articulated robots are the most common robots used in manufacturing processes. They are used to perform more complex operations such as welding, product assembly, and machining. EOATs mounted on articulated robots are designed to have a full six degrees of freedom. The robot arm consists of at least three revolute joints. A fourth revolute joint can be added to the wrist of the arm for rotating the EOAT. Its work envelope is also spherical, similar to that of the polar robot type.
There are several design aspects when considering a specific robot. Different applications require a certain set of performance parameters that need to be balanced with the required investment. Of course, better specifications are better, but the increase in cost is almost exponential.
This defines the ability of a robot to move and orient the EOAT across three-dimensional space. There is a total of six degrees of freedom. These are forward/backward, up/down, left/right, yaw, pitch, and roll. Depending on the design, the robot can have all six axes. The higher the number, the greater the flexibility of the robotic arm. Typical industrial robots used in simple pick and place applications have three to five axes while robots used for more versatile applications have a full six degrees of freedom.
Load capacity is the weight that the robot can carry or the amount of force that the robot can exert on a load. This specification is important in most pick-and-place applications. Generally, indicated load capacity in the machine‘s datasheet is enough, but this must not be the final value when designing a system. It is important to also note the effect of acceleration as it can induce dynamic forces. For robot arms supplied without a dedicated or attached EOAT, the weight of the EOAT mounted by the end-user must be subtracted from the load capacity of the robot.
These are the two main characteristics determining the effectiveness of the robot in performing its tasks. Accuracy refers to the ability of the robot to position itself or its load at a specific point. This is measured by determining how close its final state is to a set state defined by the user. On the other hand, repeatability is the measure of how the robot maintains its final position across several operating cycles. This is measured by getting the average of the distances between the final positions of the EOAT or a point on the robot after each cycle.
These usual definitions of accuracy and repeatability are known as the static case, which only pertains to the ability of the robot to bring itself to a certain displacement. Accuracy and repeatability can also be applied to the speed and acceleration of the robot.
The work envelope is the spatial specification of the robot; this is defined by its swept area, reach, and stroke. It determines the space that can be accessed by the robot‘s EOAT. The work envelope depends on the type of robotic arm (Cartesian, polar, SCARA, etc.) and the length of its linkages. This parameter is important for machine loading and unloading applications. A robot with a large work envelope is required to cover a wider distance.
Speed and acceleration directly influence the design operating speed and throughput of the robot. These properties depend on the kinematic design of the arm and power ratings of the driver, actuators, and transmission components of the robotic system. In most applications, the maximum speed and acceleration are not specified. However, in some product handling applications, these two parameters are important. Sudden changes in speed or high acceleration can exert forces on the product that can compromise its structure, containment, or quality.
Controller specifications refers to the robot‘s program structure, programming language, memory capacity, human-machine interface (HMI), internal sensing or perception capabilities, and so on. Each application may require a different controller specification. A simple pick and place application may only require the crudest form of programming. But for high precision manufacturing, more sophisticated software and hardware are required.
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