In its simplest form, OEE requires two basic pieces of information from each machine or process that are collected chronologically and stored in a database
- State Change
- Production of a Part
Ideally, these data can be pulled directly from a CNC or PLC Controller electronically. If this is not possible, then signals internal to the machine control panel or signals from external sensors can be wired to some form of data collection unit that sends information to the network electronically.
These data do not constitute OEE metrics. OEE must be computed from machine performance data and production scheduling information using complex software.
Many times management desires more data to be monitored such as
- Parts in Queue awaiting to be machined
- Actual Spindle On-Time in addition to load-to-load cycle time
- Multiple Quality Metrics versus single good (OK) or bad (Not OK / Reject)
- Sometimes these data are readily available. Other times it is not, and it may not be feasible to collect it. Unlike many other commercial OEE software applications, FS.Production is capable of processing data sets of different formats from different assets. FS.Production is also flexible so that new data streams can be easily handled if management determines that additional data be collected from a particular asset at a future date.
Network Data Collection using MTConnect Standard
For new factory installations, all new assets with network connectable controllers can be pre-equipped with OEE data collection capabilities that follow some corporate or industry standard format such as MTConnect theoretically allowing straightforward integration with commercial OEE software packages.
MTConnect is a non-proprietary protocol for real-time sharing of data between shopfloor equipment and computer systems.
MTConnect is NOT an electronic data collection method or data transfer method to upload machine performance data to a computer or network server.
Many machines that require monitoring are still in use that have older CNC controllers that are not network compatible. MTConnect is therefore not directly applicable, though some of the underlying concepts from the MTConnect standard can be exploited.
OEE Data Collection for Legacy Plants
Three general scenarios for OEE data collection that can be used and are outlined below. A mix of these methods can be used by FS.Production. FS strictly adheres to the following cardinal rule when integrating OEE solutions at older plants that have been reliably making parts on mature production lines for years:
“Never attempt to modify a working PLC or CNC controller and risk taking down production”
Unless a machine controller is network compatible and is pre-configured for plug and play OEE data collection, it is best to implement a non-invasive “Bolt On” solution that will not inadvertently disrupt production or potentially impair older machines, sometimes irreversibly.
OPC Solutions: For those assets that are controlled by a CNC, PLC or PC controller that can be safely connected to a server or gateway via Ethernet, it may be possible to pull data from the process using OPC methods.
- This may require addition of a network switch in an existing machine control panel that does not have spare ports.
- If a standard data block such as MTConnect has not been pre-programmed into the CNC or PLC code, then some knowledge of the data structure is required. This is possible for PLC based controllers where ladder logic is almost always accessible. Most CNC computer code is not accessible and integration requires cooperation with the machine OEM to implement the necessary logic into their legacy code. This can be untimely, very expensive, and sometimes impossible.
- Third party OPC server software licenses such as Kepware or other are required for each asset. Most of these licenses are costly with recurring annual fees to remain in service.
- The data must still be transferred to a server or gateway using wired or wireless methods. IP addresses must be assigned to each machine thus increasing network complexity.
FSWorks Workstations can also be used for data collection from some processes. WS.com service can be used to communicate with certain network enabled machine controllers to gather necessary data without requiring a third party OPC server license.
Sometimes an RTU (remote terminal unit) or some other “black box” device can be installed into the machine control panel. Discrete signals from machine sensors or CNC / PLC controller signals are connected to the RTU using jumper wires. The RTU monitors these signals and transmits digitized data to a gateway or server, normally via Ethernet cable or WiFi.
- This method requires physical re-wiring inside an existing control panel. The RTU requires both power and a plant network connection. Problems or even damage can arise when signals are connected to both a machine controller and RTU without proper isolation.
- Finding and verifying the proper wires to jumper can be problematic, especially with older machines that may not be well documented. The required signals may or may not be available.
- Each machine or small group of machines requires an RTU and isolation devices. There may not be adequate space or power in an existing panel to properly install this equipment.
- The data must still be transferred from the RTU to a server or gateway using wired or wireless methods. An IP address is required for each RTU.
Sometimes brute force is the safest, most reliable and cost effective solution. New part present sensors (proximity, laser, RFID, vision, other) are installed onto an older machine, sometimes in parallel with existing sensors used for machine control, to monitor good part exit, part reject and sometimes next part present. Non-contact current sensing switches can be placed around a motor drive cable to monitor when the spindle is turned on and off without affecting machine control. Push buttons, foot pedals and other forms of data entry such as touch screens can be used for manual processes or for manual batch processes such as a furnace or washer. Data is recorded by a remote PLC or some other electronic black box such as an FS.RIO (remote input output) via an FS.AIM (asset interface module) and transmitted to a Gateway using radio communication or cables that are completely independent of the plant network. Direct plant network variations of this architecture can also be implemented.
- Brute force method is completely independent of existing machine controls thus avoiding potential machine down time and controller malfunction.
- Relatively inexpensive machine modifications using commonly available probes, sensors and buttons.
- Requires an independent network of data collection devices with only a single Gateway connected to the plant network in each zone. Existing FSWorks or Workstations can also be used as local gateways with the addition of a radio modem or a communication module.
Best Data Collection Architecture
A variety of the above methods may be used to implement OEE on an older manufacturing line. All of these methods require an experienced technician to figure out how each machine works and determine the best method for each process. This is followed by implementation, testing and validation which is tedious work. Once installed, the system and process is documented and easily maintained.
For most older plants, even those with newer IT infrastructure, adding hundreds of new IP addresses and absorbing this increased network traffic is not an option. Routing physical Ethernet cable and power to each asset is not practical and very expensive. Using conventional WiFi internet can be unreliable and insecure, especially in a factory environment. One alternative is to implement alternate communication schemas based on proven industrial technologies. And FS has answers for that as well.