A common application in many automated factories is conveyors. One of the common forms of conveyor motion is a chain. A chain conveyor might be used in a drying oven or similar piece of equipment. Today we are looking at a particular application using a chain conveyor where the end user was able to improve their reliability and reduce their manufacturing costs through the smart use of sensor technology.
Prior Existing Application – A Known Troublemaker
The end user is a worldwide manufacturer of consumer goods, specifically foodservice products. At one of their plants, there was an application that would periodically cause them trouble. The application was a long drying oven with a chain conveyor and the trouble point was that if certain components became misaligned, it was possible for the chain to work its way slowly sideways, and off the rollers. This had happened in the past. Not only was it expensive to repair, but it was also time-consuming and costly in lost production.
Limit switches had been placed on each side of the conveyor to monitor for imminent failure. Unfortunately, due to the hot, dirty, and damp environment, the limit switches failed over time. Even though the limit switches were supposed to be checked periodically, this didn’t always happen as it was supposed to.
Photoelectric Sensors with IO-Link – The Problem Solver
In the interest of proactively avoiding future machine failures, a team of automation specialists looked at the application. It was determined that one possible solution could be a remote sensor, like a laser photo eye. This device works such that a light beam could be broken if the conveyor crept over. The team looked at the technology, then looked at the application again. In a dirty environment, a photo eye would get dirty over time and be just as unreliable as the limit switches.
The team brainstormed. What if we could have a device that was smart enough to know when it was dirty enough to impact functionality? What if we could have a device that was smart enough to alert maintenance that this part needs to be cleaned? This technology does exist.
The key is IO-Link. IO-Link allows a typically on/off sensor to collect important analog data through a serial connection. Critical sensors can give the PLC important status information, not just discreet on/off signals. In this application, the amount of light being received back from the reflector is tracked and a low level is set within PLC programming. When the PLC notices the photo sensor is not receiving enough light back from the reflector, a flag is triggered to have the parts cleaned.
This solution used Bulletin 42JT sensors with IO-Link. These are also known as VisiSight™ Sensors and you can read more about them here. The tracking of received light was just one function of the sensor, very much a preventative maintenance function. The primary function of the sensor was to monitor the chain on each side of the conveyor. In the case of a chain drifting laterally, the sensors will avoid imminent failure and prepare the machine for a safe shutdown.
The end user improved reliability through proactive and continuous monitoring of their sensors. The end user reduced their manufacturing costs through smart machine maintenance and avoiding costly line down situations.
Additionally, the end user chose to have LEDs on the sensor be set to blink to make it easier for the maintenance crew to locate the devices as part of the cleaning process. IO-Link provides the benefit of two-way communication. If the sensor fails, not only will the PLC be made aware, but the replacement sensor will be sent the correct settings and automatically configured.
What is IO-Link?
IO-Link is a worldwide open-standard protocol (IEC 61131-9) that allows sensors to easily integrate into a control system. Rockwell Automation is the only supplier that offers the controller, IO-Link master, and IO-Link sensors. This is key for integration, especially with Studio 5000 Logix Designer™. You can learn more about IO-Link here.
The team of automation specialists working on this project looked at further functionality of IO-Link technology. Features that were not used in the above application, but important to be aware of include:
- Changes can be made to the setting on a sensor from the PLC. If there are multiple types of parts run on a machine, at different shifts, the PLC can push out different settings for different part types.
- Descriptive tags are generated automatically in the Logix programming to make set up and maintenance easy.
- Application specific names can be given to sensors in Logix. So rather than trying to figure out where sensor #123 is, you could call it something descriptive like “conveyor 3 input”
- Real time diagnostics. Certain information will be stored outside of the PLC that may be helpful for trouble shooting. For example; how many times a sensor is triggered, duration of a trigger, time stamps of triggering, internal temperature in the sensor, and other info to notice trends in the automated process.
- Device locking, so operators cannot change sensor settings.
In closing, it is worthwhile to note that all of the above is done with standard part numbers and connectors. No special sensor part number is required! There is no difference between the sensors and cord sets already being used, an end user will simply choose to ‘activate’ the IO-Link technology for your critical sensors. This is done by introducing a remote IO device called an “IO-Link Master”.
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Do you use photoelectric sensors? Have you ever had issues with sensor failure? Let us know in the comments.