Krispy Kreme’s Drive Retrofit

Doughnuts are, obviously, the first thing that comes to mind when you hear the name Krispy Kreme. But for those with an interest in automation and manufacturing, you’re missing a big part of the Krispy Kreme story if you’re not familiar with the company’s machine building operations.

This aspect of Krispy Kreme’s operations is nothing new, as the company has designed and built proprietary machines from the company’s early days. Today, the company’s headquarters in Winston Salem, N.C., is home to a 105,000-sq.-ft. manufacturing facility that houses research, design, testing, engineering, and production operations.

John Priddy, Krispy Kreme fabrication manager, installs the G120 kit into the fryer section of a doughnut machine. Source: Siemens

The machines and processing equipment built there use Siemens drives and controls, integrated by Think PLC, the automation engineering consultant to Krispy Kreme.

“They engineer and manufacture all of their production machines, from extruders and conveyors through to the packaging, including their famous glaze waterfall,” says Bobby Cole, president of Think PLC.

Cole says the speed at which an extruded doughnut moves through the store is “a very, very big deal. Throughout the process, the shortening is kept within an exact range of temperature. Doughnuts are cooked on both sides for a precise number of seconds on each side and the cooling conveyor cycles through the store at a set number of minutes.”

Updating via retrofit

Recently, Krispy Kreme has been updating its manufacturing operations based on insights from the company’s service technicians, store managers, and customers. Patrick Betson, Krispy Kreme’s director of equipment manufacturing, says this feedback has led to several improvements addressing increased uptime and mean time before failure.

“Before there was much publicity about Industry 4.0 and IoT (Internet of Things), Bobby Cole and I often talked about the data that could be generated by more advanced machine monitoring,” says Betson. “It became increasingly clear that by integrating the latest Siemens drives and controls on our machines, and connecting them using Profinet communications, we could start putting that data to work.”

To enable consistent automation upgrades and retrofitting at existing stores and plan for the roll out of equipment at new stores, Think PLC needed to determine the fastest and most cost-efficient way to integrate Siemens Sinamics G120 variable frequency drive (VFD) technology in more than 600 stores worldwide.

This led Betson and Cole to develop a retrofit kit that would allow every store to quickly add new components and software to their existing hardware.

The key to Think PLC’s retrofit idea was to leverage the SD cards used on Siemens drives and controls already in Krispy Kreme stores. The was a viable approach because Krispy Kreme maintained each store’s unique set of machining and processing parameters on the SD cards. As a result, stores only need a local contractor to upgrade the legacy control panels, including parts for safety and power wiring.

Betson and Cole retrofitted every Krispy Kreme store in Australia in five days using their technology retrofit kit concept. Source: Siemens

“The main purpose of the kit was to replace the older Siemens Micromaster drives with Siemens Sinamics G120 drives,” Cole explains. “The SD card in the kit has software that we modified; and with a couple flips of some switches, the drive is automatically programmed. Someone with absolutely no control experience can reload the new software into the new drives and the new PLCs.”

According to Cole, the retrofit kit enables a store to replace its drives and controls in about two hours—saving significant time and costs associated with having a control technician travel to a Krispy Kreme store to perform the work.

To prove the retrofit kit concept, Krispy Kreme and Think PLC tested the kit’s installation and use in their manufacturing plant in Winston-Salem, N.C., followed by tests at various stores in the region. During these tests, the new drives and PLCs installed smoothly and the SD cards automatically updated and matched all previous store parameters. To further test the concept, Cole and Betson retrofitted every Krispy Kreme store (more than 30) in Australia in five days using the kits.

Fry control

During the doughnut frying process, the pumping of heated shortening is critical to maintaining optimal doughnut quality and product count. When the flow rate is not maintained at the desired constant, viscosity issues become a problem as dough bits cannot be filtered out of the melted shortening properly. This leads to temperature variances, causing hot spots to develop.

The Sinamics G120 drive addresses these pump motor issues while reporting the operational status of each motor. The drive also ensures that pump motor temperatures are kept below the threshold for heat damage.

Cole explains the drive can address pump motor issues through its ability to set and hold a curve that assures the most efficient flow at a low speed and a high speed—from 7 hertz to 90 hertz. With the new drives, “accuracy of the fry time has increased by 12%, resulting in a more consistent product with less waste yield,” he says. “A big advantage of the drive is that it can run a motor slow without the usual rise in motor temp. When you run a motor at very low hertz, it generates a lot of eddy current. It gets so hot, that you can’t touch the motor. And when you overheat the laminations of a motor, you greatly decrease the life of the motor. But we can monitor each drive through the Siemens TIA (Totally Integrated Automation) portal, and we’ve seen the amperage reduced by almost 17%, and the temperature of the motor reduced by 34%. We expect this will more than double the life expectancy of every pump.”

The Sinamics G120 drives also address worker safety issues through their triple-quadruple redundancy, says Cole. “The new drives and PLCs being retrofitted into every store integrate with the existing Siemens safety monitoring circuitry, including the automated safety mechanisms and E-stop buttons. For example, if a hose were to break on the shortening pump, the flow stops within 100 milliseconds,” he says.

Remote access via TIA

Using Siemens TIA portal, Think PLC can access any of the Siemens G-120 drives remotely.

Cole describes using the TIA portal via his smartphone as being like standing in a Krispy Kreme store at the drive’s operator interface.

A store can produce a thousand dozen doughnuts per hour. Pump motor drive performance in the store can be seen through the Siemens TIA portal to diagnose, troubleshoot, maintain and prevent disruptions to production flow. Source: Siemens

“When you open the door to the drive, a large display presents any fault messages,” he says. “You select a fault message and you’re given the related fault code that, in the past, you would need to look up in the user’s manual. Now, all the information you need—the details, what to check, how to reset—are on the display. Diagnostic screens help you debug the problem. Beyond this, faults and alarms can be data logged in the cloud so that trends can be studied over the course of a year and faults for a particular machine can be identified and addressed. I can also look at how many cuts were made on the extruder today. I can look at how many faults occurred throughout the day on that machine. I can see what the average temperature was in the shortening tank. I can call the local service manager and say, ‘Hey, next time you do a preventative maintenance at that store, you need to send a new pump motor, because you’re getting multiple faults within a short period of time. Have those parts on your truck and you won’t need to make a second trip.’”

Read more about the Siemens G120X drive series.