Trelleborg Shares Insights on Sealing Needs for Industrial Robots

A robot is defined as a mechanical machine programmed to automatically perform production related tasks. Industrial robots are a form of flexible automation since they are reprogrammable and can be used for many different types of applications. Extremely effective for increasing productivity, they produce high-quality products and reduce costs, making robots the preferred choice of automation for manufacturers. In this article David Kaley, Trelleborg’s global segment manager for industrial automation, explains the different kinds of robots used in industrial automation, their components and the kinds of sealing elements needed to help ensure precise performance results.

Industrial robots have five main components including:

Controller: The brain of the robot contains software that determines the robot’s actions. Key functions of the controller include motion control, sensor integration, task execution and communication with other systems.

End-effectors: Attach to the end of an industrial robot’s arm and are responsible for interacting directly with workpieces. The application determines what kind of end-effector should be used. 

Robotic manipulator: Also called a robot arm, the manipulator is responsible for moving and positioning the end-effector. It is designed to mimic a human arm but can vary depending on the type of robot.

Drive: Refers to the system that powers and controls the movement of a robot’s joints and actuators. There are several different types of drive systems, each with its own advantages and applications. 

Sensors: May consist of cameras or microphones providing robots with environmental feedback.

Robots for industrial applications include:

Articulated robots: The most common robots used in industrial automation. They have rotary joints connecting different links and are designed to mimic human arms. Each joint is referred to as an axis with independent movement. Articulated robots typically have three to seven axes with some robots for specialized tasks having over ten. Six-axis robots are the most popular because they have the largest range of motion. Articulated robots are used in welding, assembly, material removal, painting and foundry. 

Collaborative robots: Collaborative robots (cobots) use collision avoidance technology to safely operate amongst humans without barriers. Their advanced sensors can detect when there is an intrusion in their workspace causing the cobot to either slow down or stop depending on how close it is to a person or object. Cobots also have rounded designs offering gentler interaction should human contact occur, and their wires and motors are all internal to prevent possible human exposure. Sensors enable cobots to detect any abnormal force applied to their arm while in operation and adjust accordingly to changes by stopping or slowing down.

Gantry robots/Cartesian robots: A gantry robot system features a robotic arm (manipulator) mounted overhead onto a linear rail which guides the robot across a horizontal plane. Their axes are located above the robot’s operational space (work envelope) making them ideal for large overhead processes. Gantry robots are ideal for pick and place and part loading and unloading applications. Other uses include dispensing, assembly, material handling, palletizing, packaging and cutting. Gantry robots and cartesian robots are similar with the main difference being that gantry robot systems feature two X axes instead of a single X axis like cartesian robots. This extra X axis allows for larger load capacities and is the reason gantry robots are commonly deployed for automated pick and place. The additional X axis also allows for longer stroke lengths—the maximum distance a linear actuator in a robot can move its output shaft from a fully retracted to fully extended position—and higher operating speeds. This versatile and cost-effective automation option makes gantry robots highly desirable to manufacturers. 

Delta robots: Typically have three to four carbon fiber, lightweight arms that extend downward from the main robot body. Because of this design, delta robots are often referred to as spider robots. They are jointed in the middle, bending inward and connect to a small tooling plate where the end-effector can be attached. Each arm is connected to a motor located in the main robot body. The motors coordinate up and down motions of the arms pushing their joints in and out. Delta robots are known for their high speed and acceleration. Since delta robots have motors in the main body above the work area, the weight of the robot stays stationary. All movement comes from the light robot arms, allowing for low inertia, fast operating speeds and acceleration. Most industrial robots have motors located in the arm for heavier payload applications. However, this adds additional weight and prohibits fast speeds. Delta robots are ideal for assembly, dispensing, pick and place, material handling, part transfer and packaging.

Automated storage and retrieval systems (ASRS): Enable users to store items efficiently and securely in a compact footprint. ASRS handle different volumes, types and velocities of non-palletized inventory at variable speeds to accommodate varying throughput demands. Floor robots such as automated guided vehicles (AGVs) and autonomous mobile robots (AMRs) are types of ASRS.

Automated guided vehicles (AGVs): Material handling systems or load carriers that travel autonomously throughout a warehouse, distribution center or manufacturing facility without an onboard operator. AGVs are used for tasks typically handled by forklifts, conveyor systems or manual carts moving large volumes of material in a repetitive manner.

Autonomous mobile robots (AMRs): A type of robot that can understand and move through its environment independently. AMRs differ from AGVs because they do not rely on tracks or predefined paths and often require operator oversight. AMRs use a sophisticated set of sensors, artificial intelligence, machine learning and compute for path planning—the algorithms and computational processes used to determine a collision-free path for a robot to move from a start point to a goal point—to interpret and navigate through their environment untethered from wired power. If AMRs experience an unexpected obstacle, they use their cameras and sensors to slow, stop or reroute their path.

Sealing needs for robots

Robots in industrial applications need to operate with precision to accurately perform within their work envelopes at specific speeds and accelerations. This type of precise movement requires the help of several seals. Mini and nano radial oil seals are found in each of the robots’ joints keeping lubrication in and contaminants out. They also help prevent energy loss caused by friction, breakout force and drag torque. Breakout force is the amount of force required to initiate the movement of a robot’s end-effector or a specific joint from a stationary position. Drag torque refers to the resistive torque that opposes the motion of a robotic joint or actuator. 

The extremely small profiles of mini and nano radial oil seals also help manufacturers on the quest for weight reduction. These radial oil seals reduce the amount of metal and therefore weight of the robot. Lighter robots require less energy to operate and contribute to greater energy efficiency. 

The operating demands of a robot often exceed the ability of a standard radial shaft seal and radial oil seal and require the use of more advanced solutions. Trelleborg’s PDR class seals use polytetrafluoroethylene for the seal lips which can reduce friction while maintaining similar sealing characteristics to radial shaft seals and radial oil seals. 

Since robots typically have very high operating speeds, it is common to move beyond the PDR seal to the Roto Variseal style of product. The Roto Variseal has a single-acting sealing element comprised of a U-shaped ring and metallic energizing finger spring. It offers low friction with no stick-slip—a sudden jerking motion that happens when a robot transitions from static friction (stick) to dynamic friction (slip)—minimized breakout force and high wear resistance. The constrained flange eliminates potential seal rotation and is resistant to most liquids and chemicals. 

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