Factories incorporating industrial automation into their manufacturing processes continually strive to improve efficiency through increased speed and greater precision. Often, the most direct means to achieve these goals is reduced weight and increased stiffness of the robotic components, particularly the robotic end effectors. Lightweight end effectors translate directly to increased speed and higher precision on the production line, reduced motor and actuator loads, and improved reliability.
What Is an End Effector?
The capability of industrial automation continues to grow, driven by a skilled labor shortage and the development of disruptive technologies such as AI, edge, and cloud computing. Now embedded into most industries, automation technology is already on a solid footing and is marching through the global industrial complex. The physical tip of the spear in industrial robots is the end effector, also known as “end of arm tooling” (EOAT). This automation component is the part of the robot that works on the part being fabricated or assembled. It can undertake many different functions as it interacts with the manufacturing process. For this reason, end effectors are often designed specifically for a particular operation and have far more diversity than the robot arms that deploy the end effectors.
The design of the end-of-arm tooling considers factors about the robot tool’s job but also about how the work done by the end effector will impact the robot arm. Increasingly, robots are working in collaboration with humans (these are called “cobots” or collaborative robots), so the end of arm tooling must also be made safe for that interaction.
What Are End Effectors Used For?
End effectors are incorporated into various tasks in the industrial environment. There are end effectors that perform process tasks, those designed to lift, manipulate, and place parts, and robot arm tooling that performs inspection or data collection tasks.
What Types of End Effectors Are Available?
Three common categories of robotic end effectors are grippers, process tools, and sensors. Where grippers handle materials, process tools work on materials, and sensors measure the state of materials.
Grippers
Gripper tools pick up and manipulate parts in sorting, packing, or assembly operations. Depending upon the nature of the part, the robotic gripper type will be tailored to manipulate it optimally without damaging it. Various gripper types can pick up items as delicate as an egg and manipulate complex objects weighing hundreds of pounds. Design factors involved in gripper design include:
Grip force: Some applications require a light touch, while others can tolerate a wider force range.
Gripper stroke: A large stroke would be necessary if the end effector has to pick up small and large objects.
Grasp precision: A high-precision gripper will be required if the parts need to be picked up in a particular spatial orientation or if there are sensitive areas of the part that cannot tolerate interaction with the gripper.
Size and weight: Since the maximum allowable lift capacity is usually set by the robotic arm, the weight of the gripper end-effector reduces the useful load capacity of the system. For this reason, lightweight grippers are often preferable. Likewise, grippers are often required to pick or place a part into a box corner or other tight spot. A smaller gripper is advantageous for these applications, especially if it can eliminate an extra degree of motion freedom.
There are several different types of grippers used in industrial automation that can be classified as follows:
Mechanical Grippers: These are claws actuated using belts or a hydraulic system. Depending on the job, they can have two opposing fingers or many fingers, which can be large claws or needle grippers, depending on the task.
Magnetic Grippers: A controllable electro-magnet on this end effector allows the machine to pick up and drop parts made of ferrous metals.
Vacuum Grippers: Often used to pick and place items with flat faces, such as cardboard boxes, this end effector uses a suction force to pick up and drop its target from a belt into a crate, for example. These are often deployed on cobots.
Electric Grippers: These grippers use a servo motor or electromagnetic actuator on the end effector to provide the grip force. This type of gripper is often used in higher-precision applications.
Pneumatic Grippers: Using compressed air, the fingers of these grippers can be simple claws or be made of rubber-like material designed to be anisotropic that inflates to effect a gentle grip force on compliant parts such as baked goods.
Process Tools
Another class of arm tooling is those that alter a part, like sanding, polishing, welding, cutting, applying glue, building melted plastic (3-D Printing), and more. Careful thought is given to the environment where these end effectors operate — including very high and very low temperatures, dirty, corrosive, and high levels of EMI — to design them appropriately. These are the types of hazardous environments where industrial robots have high value since they eliminate risks to employees. Many of the design challenges these robot tools present involve material compatibility, reliability, control and consistency of the applied force, and other factors that impact final part quality.
Sensors
Finally, the third class of robot end-effector functions includes data collection using sensors. While this function is often embedded in the other two classes of end effectors —grippers and process tools — there are also many standalone end effectors dedicated to data collection, such as cameras. Other sensors employed on end effectors include force/torque, proximity, light, and magnetic field sensors[1]. One well-known sensor end effector mounted on the Mars Rover’s robotic arm contains a microscopic imager and two different kinds of spectrometers. The other end effector on the Rover is a Rock Abrasion Tool, which fits into the Process Tool category.
Advantages of Carbon Fiber in Robotic End Effectors
A universal principle to most engineering design is that — all other attributes being equal — a lighter part is preferable. Carbon fiber composites are attractive to the designer due to their high stiffness-to-weight ratio (specific modulus). When used to construct end effectors, the high specific modulus of carbon fiber composites impacts many aspects of the automation system. Not only does a lighter end effector increase the maximum useful payload of a robotic system, but it also increases the maximum speed of the robot arm and, in turn, reduces the energy and time required to move the arm. These outcomes drive an increase in operational efficiency: one study attributed a 40% reduction in energy consumption of a simple pick-and-place operation to using a carbon fiber end effector.[2]
Carbon fiber composites, being effectively unreactive, also provide a path for designing end effectors deployed in corrosive environments. Since removing human exposure to hazardous environments is a principal justification for industrial automation, carbon fiber composites are an essential component in the end-of-robot arm tooling designs that are robust enough to withstand these challenging applications.
Design Considerations for Carbon Fiber in Robotic End Effectors
The wide range of process and inspection operations that can be accomplished using industrial automation leads to various design considerations. The following are some ways that the material properties of carbon fiber composites can solve multiple design challenges.
Temperature
Carbon fibers can withstand very high temperatures, but the performance of commonly available carbon fiber composites is limited by the low Glass Transition temperature of the epoxies in their matrix. There are, however, carbon fiber composites that maintain most of their stiffness at temperatures as high as 500 F through the use of special high GTE resins such as phenolic.
Carbon fiber composites can have a range of low thermal expansion coefficients, depending upon the fiber and resin used. Still, they can generally be significantly more dimensionally stable than metals. Some carbon fibers can have a negative coefficient of thermal expansion, and a composite that has a near-zero thermal expansion coefficient can be created by mixing fibers in a laminate.
In any case, the thermal stability of carbon fiber composites is generally considered desirable in the design of robot end effectors, especially those that operate in a dynamic thermal environment. In such an environment, an end effector of carbon fiber composite will experience smaller thermal deflections, resulting in stresses and bolted connections requiring less maintenance.
Conductivity
The thermal conductivity of carbon fiber composites varies depending upon the formulation. Still, they are generally less conductive thermally and electrically than metallic materials and are also non-magnetic. This is desirable for end effectors deployed in an electrically unshielded environment or with high magnetic fields.
Anisotropy and Yield Strength
Compared to isotropic metals, the anisotropic nature of carbon fiber gives the designer another knob to turn to minimize deflection. Additionally, the viscoelastic nature of some epoxy resins can give carbon fiber composites damping properties that can be advantageous in many precision end effector applications. Further, unlike metals such as steel and aluminum, carbon fiber does not noticeably yield before it breaks. This property allows the designer to access higher forces using carbon fiber composite gripper components, for example, and it also provides for reduced damage in unintended robot end effector collisions.
Robotic End Effector Design and Manufacturing
Element 6 Composites works with companies in the injection molding, beverage, and consumer products industries, as well as companies specializing in the design and fabrication of automated systems, to replace metal end effectors using carbon fiber composite manufacturing. Substantial decreases in weight are possible with optimized composite systems, with weight reductions of 50% or more common.
Leveraging in-house finite element analysis, CAD design, and tool making, Element 6 Composites regularly works with customers to produce highly specialized lightweight end effectors. If your company wants to learn more about using custom carbon fiber composite manufacturing in robotic end effectors and automation, please contact us to discuss your specific application.
References
Chun, Carrington, David A. Guerra-Zubiaga, Garrett Bailey, and Kathryn Bharadwaj. “High Efficiency Manufacturing with a Smart Carbon Fiber End Effector.” Paper presented at the ASME 2022 International Mechanical Engineering Congress and Exposition, 2022.
Okayasu, Mitsuhiro, and Yuki Tsuchiya. “Mechanical and Fatigue Properties of Long Carbon Fiber Reinforced Plastics at Low Temperature.” Journal of Science: Advanced Materials and Devices 4, no. 4 (2019/12/01/ 2019): 577-83. https://doi.org/10.1016/j.jsamd.2019.10.002.
“What Are End Effectors in Robotics? Types of End Effectors, Applications, Future.” 2023, accessed 12 December, 2023, https://www.wevolver.com/article/what-are-end-effectors-in-robotics-types-of-end-effectors-applications-future.
[1] “What are End Effectors in Robotics? Types of End Effectors, Applications, Future,” 2023, accessed 12 December, 2023, https://www.wevolver.com/article/what-are-end-effectors-in-robotics-types-of-end-effectors-applications-future.
[2] Carrington Chun et al., “High Efficiency Manufacturing With a Smart Carbon Fiber End Effector” (paper presented at the ASME 2022 International Mechanical Engineering Congress and Exposition, 2022).
