Productivity increases with cloud-connected IPC

Each instance of every product in restorative dentistry requires lot-size-one manufacturing, including for dental prostheses (restorations) such as crowns, bridges or dentures.

For Glidewell Dental, producing tens of thousands of patient-specific devices each week requires intensive engineering efforts. Glidewell’s investments in automation and Cloud-connected systems, particularly in its factory for BruxZir Zirconia restorations, is a big part of those efforts.

“We do business with some 60,000 dentists each year — or nearly 50% of all practicing dentists in the U.S. restorative market,” said David Leeson, VP, engineering at Glidewell. Flexible automation provides a decisive advantage in an industry that still relies heavily on skilled artisans executing manual processes.

Dentists either mail impressions of a patient’s oral anatomy to Glidewell or laser scan and upload 3-D digital impression images to the company’s proprietary material requirements planning (MRP) digital platform, CloudPoint, built on Amazon Web Services (AWS) Cloud.

Proprietary artificial intelligence (AI) technology generates a custom prosthetic design to match the impression and turns the CAD file of each restoration into a unique NC project. The BruxZir factory assigns a case with the prescribed characteristics such as tooth size, shade, and thickness, and selects an unrefined block of zirconia material (milling blank) of suitable size, shape, and color.

A robot transfers the zirconia blank to a milling tower for detailed anatomical shaping, after which the restoration undergoes glazing for a more natural surface appearance. Barcode scanners track the case throughout the process, and if an operator removes the case for any reason, a vision application follows the technician and case.

“To make this a closed-loop process, optical scanners generate a 3-D geometry of the finished product, and an algorithm compares it to the design file. The dental implant must be within 50 microns to pass quality inspection — and most often, it’s within 20 microns,” said Kunal Patil, automation manager at Glidewell. “Performing just the glazing by hand could create variances of up to 150 microns. PC-based automation helps us achieve much higher precision.”

However, it was not always this way. Jim Glidewell founded the company in his apartment in 1970 using traditional, painstaking hand-fabrication techniques. As his clientele grew, so too did his need for additional labor and supporting services, giving rise over the years to a highly diverse and self-sufficient manufacturing chain.

Today the Irvine, CA.-based company produces everything from raw materials to final restorations and other medical devices and employs more than 4,300 Glidewell professionals around the globe.

Following dentistry’s CAD revolution in the early 2000s, Glidewell evolved quickly to today’s Cloud-based production. “Now we are creating heavily connected systems and leveraging data from the more than 10 million individual patient designs we store in the Cloud,” Leeson said. “Our vision is to keep extending up and down the value chain to improve our current products and create new ones.”

The woes of an installed base

The machines update the Cloud database when a case moves from one production step to another, monitoring the time between steps and communicating the consequences a management dashboard.

“Since our products are produced on-demand, we always have a customer waiting for anything we make, and we cannot replace products from stock like other companies. If an order sits for too long, the system automatically adds it back to the queue. We don’t try to track the product down; we just make another,” Leeson said.

From the beginning of the BruxZir factory build, the Glidewell engineering team knew that all automation technologies needed to be flexible, scalable, and industrial hardened. The machine controllers and motion components would need to adapt to constantly changing recipes.

Glidewell soon needed to scale up from a single milling tower of four mills to five milling towers in a system and, eventually, to a second complete system of five towers, totaling 40 mills. Finally, the components needed to withstand significant amounts of abrasive zirconia dust.

As Glidewell began to implement the BruxZir factory’s first milling tower in 2018, the engineering team soon realized its standard machine control technologies were not up to the task. “We struggled with many issues involving synchronization between robots and multiple controllers, debugging, and real-time communication, while using a familiar controller,” Patil said.

Then a decision was made. “We switched to Beckhoff, ” Patil said.

Glidewell worked closely with the local Beckhoff Automation team, including regional sales engineer Charles Usher and applications engineers John Helfrich and Lauren de Rosset. Within a week, the team proved the concept using PC-based control systems. Within a month, a newly operational mill met all Glidewell’s production requirements.

Cloud-connected manufacturing

The BruxZir factory leverages multiple Industrial PC (IPC) and TwinCAT 3 automation software solutions from Beckhoff. A C6015 ultra-compact IPC, an AWS-certified device, serves as the Internet of Things (IoT) gateway, delivering NC programs from the Cloud (see Figure 1).

Figure 2: A C6930 control cabinet industrial PC (IPC) powers each line, communicating with robots, vision systems, field devices, and milling tower controllers. Courtesy: Beckhoff Automation[/caption]

Each milling tower relies on a CX5140 embedded PC to run 4-axis motion on four mills — i.e., 16 axes per controller — using TwinCAT NC I (see Figure 3). Working in concert, the PC-based controllers provide connectivity, processing power, and scalability to automate 20 mills, with 80 axes of motion, in one standard system (see Figure 4). According to Patil, the controllers also meet requirements for cost-effectiveness and durability.

Figure 4: Glidewell has implemented two complete prosthetic tooth manufacturing lines with 20 mills each in its factory for BruxZir Zirconia restorations. Courtesy: Beckhoff Automation[/caption]

“In the past, we avoided putting antivirus software on real-time systems as it harmed performance. Isolating machines on the network was still a risk, and it complicated connectivity,” said Leeson. “With Beckhoff IPCs, we can run approved antivirus software in the Windows environment. This solution meets cybersecurity demands without affecting performance.”

TwinCAT 3 provided a flexible, comprehensive engineering and runtime environment for Glidewell. Patil said his team took advantage of the capability to program the standard machine control logic, advanced CNC programs, and APIs in C# and .NET in one software platform.

“When we first started using Beckhoff technology, I had worked on just a few PLC projects, but TwinCAT made implementation easy with its Microsoft Visual Studio integration. Also, TwinCAT NC PTP follows PLCopen standards while allowing us to solve complicated tasks.”

The BruxZir milling system sends production data to the AWS Cloud for analytics, troubleshooting, and predictive maintenance using Beckhoff solutions. TwinCAT IoT and the C6015 IPC — which interfaces with AWS IoT Greengrass, the open-source edge runtime, and Cloud service — enable easier data insight discovery to boost machine performance. “Our analytics constantly monitor the average load on the motors, communicating from the milling towers to the Cloud,” Patil said. “As a result, we see if motors are performing well or if tools are beginning to wear down.”

These insights, combined with a modular system design, enable operators to quickly swap one mill for another that has been refurbished with new router bits.

Boosting milling capabilities

While TwinCAT and PC-based control enable Cloud connectivity, the EtherCAT industrial Ethernet system makes high-performance production of the dental implants possible. EtherCAT offers real-time communication rates for the plant floor, up to 65,535 nodes on one network and TwinSAFE functional safety. This fully integrated, TÜV-certified safety technology supports communication over the standard EtherCAT network and programming in the TwinCAT environment.

“With so many concurrent processes, we do not want every mill to stop if someone presses an E-stop for a particular mill. TwinSAFE allows us to stop specific mills and safety zones, and we can create that logic entirely within one project,” Patil said.

Glidewell used a wide range of TwinSAFE and EtherCAT input/output (I/O) modules in DIN rail and machine-mounted form factors (see Figure 5).

Figure 6: AX5000 servo drives and AM8000 servo motors from Beckhoff power the pick-and-place robots that feed new cases to the milling towers. Courtesy: Beckhoff Automation[/caption]

“If the motors deviated even slightly, our final product would not match the design file, or the material could chip and show defects even from minor vibrations,” Patil said. “Maintaining the required high precision is no problem for EtherCAT and the Beckhoff servo motors. We run the motors at a cycle time of 250 microseconds, which we could actually cut in half if needed.”

Replaced legacy controllers

Each mill completes a case in roughly 10 minutes, maintaining round-the-clock production. Following the success of the first line with PC control and EtherCAT, Glidewell completed another line of 20 mills. The company is now implementing a third full line, reaching a total of 60 mills.

Glidewell scaled production without sacrificing performance or quality. Data from each mill is sent to the Cloud every two seconds, which allows the company to eliminate downtime through predictive maintenance and continue to act on valuable production data to enhance products.

PC-based automation cut the number of components required, according to Leeson: “Our previous controllers could only handle a single mill each, where the Beckhoff controllers operate four mills each. In addition, to achieve the same data acquisition and Cloud connectivity, the previous controllers would have required a separate PC.”

Patil said other control options Glidewell explored cost nearly twice as much to achieve the advanced functionality standard in the Beckhoff IPCs and did not have native support for Windows. In addition, each of the EL7211 and AM8000 servo components has exceeded 100,000 hours of nearly continuous operation without failure.

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