Improving System Efficiency Using Automation

By Jeff Hale

Improving the efficiency of a powder coating line is very important. Those companies taking the time to investigate and implement new tools and automation concepts will find their products being produced with a superior looking finish while realizing improved performance in finishing line operational costs.

Many users of powder equipment have taken the time to evaluate new spray guns, recovery booth technology, and automation. Those that have invested in these items realize many benefits like improved film control, reduced material usage, lower operating costs, and extended equipment life.

Another key to improving system efficiency is to utilize automation. Automation includes the use of a controller to operate gun controls, gun positioning, airflow controls, and other system variables. The use of controllers is more popular with many users of new powder systems, but a large portion of the industry is not using automated controls to improve the efficiency of their systems. There is real value in having powder guns turn on and off or if applicable, move in and out. Many users don’t understand these advantages and choose to ignore them.

Controller Definition
A simplistic definition is that a controller is an industrial computer replacing complicated hardwiring with "soft" wiring. This soft wiring is a program that simulates an electrical circuit. A controller takes input and then controls output to the system components. Examples of the types of controller inputs are push buttons, pressure switches, photo sensors, or relay contacts.

Example outputs can be indicator lights, relay coils, or motor starters, while other types of devices that can be monitored and controlled are analog. Examples of these analog devices might be pressure sensors, position transducers, temperature sensors, and variable speed motor drives. In most cases, the equipment controlled in a hardwired system is essentially the same as in a controller system. The difference is the flexibility that is afforded.

Powder Delivery
Probably the most popular area of the powder coating system for control is the application of the powder itself. Automating this process can show immediate savings in powder utilization and component wear. In most cases, this process can be easily retrofitted to existing systems. Finish quality is improved by optimizing the operation of the powder application guns (Figure 1). The most common implementation is automated triggering of the powder coating guns. Two methods for automatic triggering are zone triggering and style triggering.

Zone Triggering
Zone triggering refers to triggering the guns based on the part profile. A typical application uses photo sensors to scan the product as it enters the powder coating booth (Figure 2). The photo sensor information is stored in the controller and creates a digital “image” of the product. This information moves through the controller memory in sync with the conveyor travel. An encoder mounted to the conveyor is used to supply conveyor movement information. As the product approaches the powder coating guns, the controller regulates when each gun is individually triggered. Based on its proximity to the product, the gun is triggered on when the product reaches a preset distance to the gun. This distance can be positive or negative and is in relation to the leading edge of the product. The gun is triggered off when the product trailing edge reaches another preset distance to the gun. Again, this distance can be positive or negative. By modifying these lead and lag distances, the application can be optimized to improve transfer efficiency and powder deposition.

The photo sensors typically represent the zones. If a booth has five photo sensors aligned vertically, it is said to have five zones. By assigning active zones to each gun, a gun will only trigger when the product has passed through the respective zone. This allows only the guns needed for a given product to be triggered, which again improves transfer efficiency.

Style Triggering
Style triggering is most effective for product that requires guns to be triggered at precise locations on a product or multiple times across a product. Rather than scanning the product to determine the leading and trailing edges only, sensors are used to identify the specific product style. When the product reaches the correct proximity to the gun, a triggering recipe is called up within the controller and the gun is triggered accordingly. Style triggering does not rely on the part profile for triggering and is generally synchronized with the product carrier. Multiple style recipes are stored in the controller and are entered through the operator interface.

Gun Positioning
Coating performance is greatly affected by the position of the gun in reference to the product. If the product width varies greatly, guns need to be repositioned for proper target distance (Figure 3). Allowing the controller to handle this function reduces the workload on the user and enhances performance.

Typical applications use light curtains to detect the width of the product as it enters the powder coating booth. In a zone triggering system, as the product passes through the booth, the guns are positioned in or out to maintain an optimal target distance. The positioning equipment can be pneumatic or electric motor driven. Positioning parameters are entered into the controller through the operator interface similar to the zone triggering parameters, although normally not having negative values. This prevents the guns from being in a position that could cause a collision.

Style Based
In a style-based system, the positioning devices may be programmed to override the actual profile of the product. Also, if the positioning devices have more than a single axis, the guns can track with the product as it passes. Inserting guns into cavities and recesses is a common application.

Articulated robots, those with rotary joints that allow them to move in a wide range of directions, are sometimes employed to target difficult areas. Program parameters are passed to the robot controller from the master controller as the product style changes.

Product Identification
Automatic gun triggering and positioning is dependent on the accuracy of the product identification. Photo eyes, light curtains, ultrasonic sensors, and others are employed to supply information to the control. Selecting the appropriate equipment is very important. The product mix to be identified determines the sensing method needed.

Operator Interface
There are multitudes of configurations for operator interfaces. A control system is no longer limited to just push buttons and indicator lights. Real-time data from the controller can be displayed, monitored, and modified through a graphical-type interface in a format that is easily understood by the operator. These systems offer the user a much higher level of functionality and connectivity. Data from the controller can be written to a mass storage device, such as a hard drive or flash drive. Recipe data can also be stored on the controller and written on an as-needed basis. The logging of system status, history, and faults to the controller greatly enhances the maintenance of the system. By interfacing the controller to a network, data can be read into other remote controllers. Data can be read directly into common controller application programs, such as spreadsheets. Controllers used in conjunction with computers will greatly increase the systems capabilities by increasing data acquisition, storage, and trending information needed today by many companies for Statistical Process Control (SPC) and/or internal ISO 9000 reporting.

Security measures can be employed on the operator interface to prevent unauthorized modification of controller data. Passwords are employed to restrict access to given areas. Access to these areas can be logged to the controller as a permanent record. Using a controller for an interface can also greatly improve the appearance and usability of a system. Color displays and animated graphics help to provide information in a user-friendly manner.

Controllers offer a unique feature to the complete system; however, they are not without their faults. The controller is subject to things like lightning strikes, or even psychical damage. If the system is designed without redundant manual hand-off controls, and the controller is damaged, your system can be rendered inoperable until a replacement is installed. Having current program backups on hand is important so that should a program reload be needed, your system can be up and running very quickly.

The Bottom Line
As stated in the beginning of this article, improving the efficiency of a powder coating line is very important. Those companies that take the time to investigate and implement any of these tools and automation concepts will find their products produced with a superior finish while realizing improved finishing line performance. Those that choose to do nothing regarding automation will continue to find their operational costs spiraling out of control.

Jeff Hale is director, marketing for Gema USA Inc.