Designing Joint Seals for Cobots and More

Summary

Editor’s note: Automation.com had the opportunity to talk with subject matter experts at Freudenberg Sealing Technologies about how the company developed a Z-shaped cobot joint seal as well as other robotics-related topics.
 
Sometimes traditional solutions no longer meet real-world situations. It is those situations that drive innovators to go beyond the status quo to create something really remarkable. When a collaborative robot (cobot) manufacturer needed help with the joint seals for its newest product line, it turned to an experienced innovator for help.

Cobots: Sharing work and space with humans

Cobots are intended for direct human-robot interaction within a shared space or where humans and robots are in close proximity. Traditional industrial robot applications, on the other hand, require robots to be isolated from human contact or for humans to be protected by cages or guards.

Typically, cobots help automate unergonomic tasks such as helping people move heavy parts, machine feeding, or assembly operations. Cobots must be adaptable for use in different work environments like welding cells and packaging lines. They also must be fast, flexible and able to work hand in hand with people in many work situations.

As with traditional robots, cobots have joints, which allow for movement in multiple axes. To ensure longevity, cobot joints must be sealed to industry standards. The goals for cobot joint seals are to provide the required ingress protection while minimizing friction during movement. A product with an IP54 protection rating is protected against dust ingress sufficient to prevent the product from operating normally. With an IP54 rating, the product is fully protected against solid objects and the splashing of water from any angle.

Historically, the cobot manufacturer in this case had used simple PTFE rings rather than IP54-rated seals in an effort to ensure that the efficiency, energy consumption and speed of motion of the cobot arms were not compromised. In addition, high travel speeds and forces generated in the cobot arm create an environment with temperatures as high as 140 degrees F (60 degrees C). Any seal must withstand these temperatures over the long term. And since extremely low material elongation is also important, any seal chosen must guarantee functionality in each operating mode and at all temperatures.

The cobot manufacturer needed a design service partner that could develop a proven sealing solution to meet all these goals.
 

Creating a sealing solution

The cobot manufacturer chose Freudenberg Sealing Technologies as its design service partner because of Freudenberg’s track record, development expertise and the stellar reputation of its global business unit Freudenberg Xpress, an expert in small and medium batch sizes, rapid prototyping and customer-specific sealing solutions. The process of developing the solution demonstrates what it takes to get the right solution in place.

First, Freudenberg provided a polyurethane (PU) U-ring seal. However, frictional forces, which must not exceed 1 newton-meter, proved to be too great. The radial forces had to be significantly reduced, as did the contact stresses on the dynamic seal lip.

Next, Freudenberg changed the overall geometry of the seal to a Z-profile and integrated a second groove, which greatly reduced the contact pressure and met the requirement for less than 1 newton-meter of force at the moment of friction. But the level of wear was still too high because of the cobots’ lightweight, mostly aluminum construction, and surface material roughness. In response to this, the company developed a seal with a three-component solid film lubricant coating with high carbon content. The coating made it possible to further reduce wear.

With a Shore hardness of 92, the seal material in question, 92 AU 21101, is very soft and flexible. Nonetheless, its tensile strength is 59 MPa, putting it significantly above the required minimum level of 50 MPa. At minimal elongation, components made of 92 AU 21101 can be relied on in temperatures ranging from -58 degrees F (-50 degrees C) to 230 degrees F (110 degrees C). Their conformity with RoHS, 2015/863/EU and 2011/65/EU is unrestricted and unconditionally valid.

The resulting Z-shaped cobot joint seal with solid-film lubricant coating was a success, but it required the cobot manufacturer to make changes in the cobot design. Consequently, the seal geometry had to be reworked. For the final version of the cobot joint seal, Freudenberg created a Z-geometry with a further optimized dynamic seal lip. With the systematic use of finite element analysis (FEA) calculations for the lip thickness and a later simulation, unnecessary process steps were eliminated in the development of the final seal. That meant it was possible for the manufacturer to achieve significant savings related to development.
 

Customer-specific solutions

The cobot manufacturer didn’t just need seals for cobot joints. It needed the expertise of Freudenberg Xpress as a service provider to provide fast response and short development time throughout the process.

Freudenberg Xpress produces affordable, high-value CNC-turned sealing solutions. It not only manufactures prototypes, but it also handles small production runs and one-offs quickly and economically. Freudenberg Sealing Technologies applies the same standards that it uses for large-scale production. It has established processes for quality assurance and lab testing, along with comprehensive onsite service in much of the world. This enables the company to design, simulate and deliver solutions in the event of requirement modifications, usually within two weeks.

Creating a new best practice, the cobot manufacturer has decided to integrate Freudenberg as a partner into the development process for its products at a very early stage. The partners’ collective experience makes it possible to consider many additional parameters in advance, which leads to shorter development times and fewer correction cycles. Products are also ready for the market sooner.
 

Rapid prototyping and small series

Freudenberg Xpress’ machining and milling technologies enable the company to produce both high-quality catalog parts and customer-specific seals. As demonstrated with the cobot joint seals, the best “product” Freudenberg has in its portfolio is not a seal, it is the ability to produce prototypes quickly and economically. Freudenberg Xpress’ customer-specific solutions can meet—or exceed—customer requirements.

Freudenberg Xpress offers high-quality sealing solutions for every part of a product’s lifecycle. It starts with a fast and cost-effective production of prototypes during the development phase, followed by small series during the market launch, and replacement parts made of the original Freudenberg materials. Finding solutions for its customers—as with the Z-shaped cobot joint seals—can turn a custom-made seal into a standard stock item.

Certain complex applications with special operating conditions require customized sealing solutions with individual sizes and designs, making a precise match to a specific application possible. A tailor-made seal can be produced by either modifying a standard component like an O-ring or by designing a completely new solution. Special adjustments are possible by complying with hygienic design standards and by preventing dead spaces. Materials can vary greatly—from elastomers like EPDM, Fluoroprene XP, or NBR to high-performance plastics such as PTFE or PEEK. Customized sealing solutions up to 2,500 mm can be machined.
 

Seals for other robot types

Industrial robots have gained a firm place in automation and manufacturing. Freudenberg Sealing Technologies’ portfolio includes robots in addition to the aforementioned cobots, including 6-axis, SCARA, automated guided vehicles (AGVs) and delta robots, according to Hunter Cheng, Global Segment Manager Robotics at Freudenberg Sealing Technologies. These robots take over physically demanding, unhealthy tasks and tirelessly complete even the most monotonous work. The Robotic Industries Association (RIA) describes a robot as “an actuator that operates in at least three independent axes to move, position, assemble, or machine materials, parts, tools, or specialized equipment.”

Six-axis robots. Today, 6-axis robots primarily support modern manufacturing processes. Exceptional robot properties, such as high precision, repeatability and speed, along with the ability to cover large work areas, enable 6-axis robots to support demanding automotive, electronics manufacturing, food and beverage, and pharmaceutical applications.

Selecting the appropriate material is critical to ensure the reliability and durability of seals for 6-axis robots. With the diverse range of applications for 6-axis robots across various industries, which have highly varied environmental conditions and requirement profiles, seals must meet the most stringent demands. In the construction industry, dust and dirt are commonplace. In foundries, high temperatures pose another challenge.

Final thoughts