Electricity and Control September 2021

CONTROL SYSTEMS + AUTOMATION

Baking the perfect loaf Bread could be considered a staple food, globally, and the baking of bread a process fundamental to daily life around the world. Bread likely brings to mind your favourite bakery. But baking the perfect loaf, and in large enough quantities, demands ovens that accurately control the process from beginning to end.This was the task faced by Mechatronics Ltd., a system integrator and official distributor of Delta Motion, Drive, Control, and Robotics products based in Bulgaria.

T he requirements for the bread baking machine defined four temperature zones. The first zone is especially powerful to compensate for the cooled conveyor belt and the relatively cool loaf entering the oven. At this step, steam is also injected into the oven to give the bread a freshly-baked sheen. It is followed by three temperature-controllable baking zones, carefully controlled to bake the optimal loaf. The conveyor belt of this travelling oven design also needs to be kept at the correct speed throughout the process. And the final element of the specifications was a human-machine interface (HMI) to configure the baking process, deliver temperature status of each zone, and output any error status information. For the HMI, the team selected the Advanced HMI DOP-107WV from the DOP-100 Series. This touch-based control panel features a 16:9 7-inch colour TFT screen with a narrow frame. With multilingual support it was well-suited for this market, and user-friendly editing software makes the final user interface easy to navigate. With several RS-485 COM ports, it could be integrated easily with the other components selected for the project. Considering the operating environment, the flat, wipeable surface of the DOP-107WV also made it a suitable choice for a dusty bakery. Control for the conveyor was implemented using an MS300 Series inverter. This ac motor variable frequency drive (VFD) also supported the RS-485 Modbus interface and is ideal for open-loop control of induction motors (IM) and permanent magnet (PM) motors.

Temperature control But it is the oven that defines the quality of the bake. Special attention was given to selecting the optimal control approach for the seven heating elements used. After careful deliberation, the DTC1000 Temperature Controller was selected as the main controller, with DTC2000 controllers used in parallel for the remaining six heaters. These are also connected to the Modbus. The selection of established, reliable components, as well as careful programming, were critical in delivering a low-maintenance design that could be operated 24/7. To provide optimal temperature regulation, the auto- tuning function of the DTC1000/2000 was used. The inputs are acquired from third-party PT100 temperature sensors and control of the heating elements is implemented with solid-state relays. Auto-tuning uses a training process to configure the closed-loop PID controller once the sensors and heaters are installed in this 250 kW oven. Further complicating the implementation was the dual heating and sensing of the last three baking zones. With one heater above the conveyor and the other below, each needs to be set to a different temperature. Spare outputs available from the Delta Temperature Controllers were linked to relays for audible and visible alarm signals. These signals were also replicated in the DOP-107WV HMI. Conveyor speed Closely linked with the quality of the bake is the speed con- trol of the conveyor belt. The MS300 VFD is linked to an inductive proximity sensor that is easy to clean and remains accurate in the dusty baking environment. Installed close to the gears, the built-in programmable logic controller (PLC) of the MS300 is configured to monitor and calculate the conveyor speed. This is continuously compared to the set- point defined in the HMI. Thus, the customer only needs to set the desired baking time, the required temperature, and then press run to start baking. The Mechatronics Ltd. team benefited from the broad range of industrial automation solutions in the Delta portfolio. Integration of the VFD, HMI, and Temperature Controller was simplified by the out-of-the-box interoperability and connectivity of the components selected. “Most people would assume that baking bread is very simple. On the contrary, the bread oven project has highlighted the skill required of both bakers and engineers to create a machine that delivers the perfect loaf. The auto-

In industrial ovens accurate temperature control through the different process zones is critical to the quality of the bake.

4 Electricity + Control SEPTEMBER 2021