EtherCAT- and PC-based control in precision milling for prosthetic tooth manufacturing
Following dentistry’s CAD revolution in the early 2000s, U.S. dental prosthesis manufacturer Glidewell Dental evolved quickly to reach its current highly automated production. Flexible automation solutions from Beckhoff have helped modernize a prosthetic tooth factory. Here, the C6015 ultra-compact IPC serves as an IoT gateway, delivering patient-specific NC programs from the cloud and transmitting production data from a total of 40 mills every 2 seconds for analysis.
Founded in Jim Glidewell’s apartment in 1970, the Irvine, California, company now has more than 4,300 employees globally, producing a broad portfolio of dental restoration and medical device products. Every product requires lot-size-1 manufacturing in restorative dentistry, when supplying dental prostheses such as crowns, bridges or dentures, for example. For Glidewell Dental, producing tens of thousands of patient-specific devices each week requires intensive engineering efforts. “We do business with some 60,000 dentists each year – or nearly 50% of all practicing dentists in the U.S. restorative market,” says David Leeson, Vice President of Engineering at Glidewell.
Dentists either mail “impressions” of a patient’s oral anatomy to Glidewell or scan and upload 3D digital impression images to the company’s proprietary digital platform built on Amazon Web Services (AWS) cloud. A proprietary AI technology then generates a custom prosthetic design to match the impression and turns the CAD file of each patient-specific restoration into a unique NC project. The state-of-the-art Glidewell BruxZir® factory assigns a case with the prescribed characteristics, such as tooth size, shade and thickness, and selects an unrefined block of zirconia material of suitable size, shape and color. A robot transfers this milling blank to a milling tower for detailed anatomical shaping, after which the restoration undergoes glazing for a more natural surface appearance. Barcode scanners and a vision application track the case throughout the process.
“To make this a closed-loop process, optical scanners generate a 3D geometry of the finished product, and an algorithm compares it to the design file. The dental implant must be within 50 μm to pass quality inspection – and most often, it’s within 20 μm,” says Kunal Patil, Automation Manager at Glidewell. “Performing just the glazing by hand could create variances of up to 150 μm. PC-based automation helps us achieve much higher precision.”
Production expansion requires increased control performance
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. Also, Glidewell 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 first milling tower in 2018, the engineering team soon realized that its legacy 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,” Kunal Patil says. “After evaluating different automation platforms, we switched to Beckhoff.”
Powerful and IoT-capable Industrial PCs
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 IoT gateway, delivering NC programs from the cloud. A powerful C6930 control cabinet IPC is the main system controller, communicating with multiple robots, vision systems, field devices and machine controllers at the milling towers. 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. Working in concert, the PC-based controllers provide optimal connectivity, processing power and scalability to automate 20 mills, with 80 axes of motion, in one standard system. According to Kunal Patil, the controllers also meet requirements for cost-effectiveness and durability.
The BruxZir factory needed to meet California IoT regulations that took effect in 2020, David Leeson explains: “With Beckhoff IPCs, we can run approved antivirus software in the Windows environment. This solution meets all cybersecurity demands without affecting performance, which is impressive.” Kunal Patil says 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.
TwinCAT IoT and the C6015 IPC – which interfaces with AWS IoT Greengrass, the open-source edge runtime and cloud service – send valuable production data for analysis every 2 s. Besides facilitating troubleshooting and predictive maintenance, this enables easier discovery of data insights to boost machine performance and improve product quality.
Precision and efficiency through TwinSAFE and servo technology
With real-time communication rates for the plant floor, EtherCAT makes high-performance production possible. In addition, TwinSAFE makes functional safety an integrated part of the control system. “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,” Kunal Patil says.
AX5000 Servo Drives and AM8000 servomotors with One Cable Technology (OCT) from Beckhoff power the pick-and-place robots that feed new cases to the milling towers. In the mills, space-saving compact drive technology with OCT is used, that is, the AM8100 series servomotors and EL7211 servomotor terminals. Here, the AM8100 servomotors have proven to be robust, reliable and highly precise in operation, while constant direction changes put substantial stress on the components. “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,” Kunal Patil describes the high requirements.
PC-based control reduces number of components and costs
The BruxZir factory achieved both the high-precision manufacturing and data acquisition capabilities after transitioning to PC-based control from Beckhoff. Each mill completes a case in roughly 10 minutes, maintaining round-the-clock production. The company is now implementing a third full line, reaching a total of 60 mills. PC-based automation cut the number of components required, according to David 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.” Kunal Patil adds that other control options that Glidewell explored cost nearly twice as much.
Glidewell continues to evaluate new Beckhoff technologies, including Gigabit communication with EtherCAT G and TwinCAT HMI visualization software, to further enhance their solutions. “Glidewell and Beckhoff have similar histories, starting with a single owner, and charting rapid growth through a passion for innovation,” Kunal Patil says. “So, we don’t see Beckhoff as our vendor. We see them as our partner.”