What it is and what its not!
It is a system with the objective of improving and optimising operations and machine efficiency on a coupled manufacturing line by making best use of current assets.
It is a real-time system which allows the visualisation and monitoring of operation on a production-line in a completely transparent manner.
It is independent of machine manufacturers and in its basic form doesn't require any physical or electrical interaction with the machine being monitored with the exception of the sensors monitoring product-flow.
It is stand-alone embedded hardware with high availability and uptime.
It is not a SCADA or database system that requires kilometres of wiring, server rooms or databases that generate weekly reports in what we call a “post-mortem” fashion.
Theory of Productive Downtime
In general, the concept of Downtime on a production-line is seen as a negative one and is to be avoided. This is always true of the bottle-neck machine, typically the slowest on the line and the one at the bottom of the V-profile, which should strive for 100% run-time. Anything less will affect Line Efficiency. However, for the other machines on the line, there is scope for Productive Downtime.
Introducing the concept of Productive Downtime.
Productive Downtime is inherent in the system operation and utilises a system’s constraints, over-capacity and acceleration capability, to predict the location and magnitude of available time at workstations.
It has evolved from production theories like JIT and Kanban which are not applicable in a high speed coupled manufacturing installation with fixed accumulation. Productive Downtime is available due to both this accumulation and stoppages on the production-line.
Coupled manufacturing refers to an installation where machines are connected to each other by conveyors or storage bins known as buffers or accumulators. A machine processes product and feeds it into an accumulator from where the next machine on the line fetches, processes and feeds its accumulator. This continues until the product exits the last machine into the warehouse.
Productive Downtime is applicable to any coupled manufacturing production line whether it consists of high-speed machines or the manual assembly of products.
Productive Downtime Defined
Productive Downtime, in the above context, is defined as the time available for a production machine operator to stop his machine without affecting the overall performance of the production line.
Importance of the V-Profile
High-speed production lines are designed such that machine throughput-rates are lowest in the centre and highest at the start and end. This is the V-profile.
The machine at the bottom of the V needs to be kept supplied with product. In a food or beverage line this is where product and empty containers meet. If it stops, production stops. The longer it runs, the more product enters the warehouse. The IPAV System monitors if the V moves from its designed position and can operate with a dynamic V-profile.
Dynamic Productive Downtime
Upstream of the V, a machine that keeps its accumulator filled is able to create Productive Downtime by virtue of the fact that its downstream machine has product to draw on and therefore stay running. Downstream of the V, machines draw product away from the V-machine to ensure it has accumulator space for its product. These create dynamic Productive Downtime.
Becoming the Constraint
Any machine that doesn't fill or drain the V-machine will become the Current Bottleneck Machine (CBM) or Current Constraint Machine (CCM). We define the CBM as the machine with the lowest Productive Downtime on the production line. This is a good indicator that the machine is not performing well. A machine transitions from CBM to CCM when it stops producing. When there's a CCM there is a direct cost to production line efficiency.
The Productive Downtime real-time advantage
Where the IPAV System has an advantage over traditional methods is that it allows the state of the production-line to be monitored, analysed and displayed in real-time at each machine. Existing technology adopts a post-mortem approach. Stoppages are analysed after the fact.
This allows the operator to make decisions based on the current state of the production-line. The operator is aware that if his machine is the CBM, stopping it will make it the CCM and impact on line efficiency. Maintenance or cleaning decisions are made based on available Productive Downtime. These all combine to improve overall line efficiency.
Static Productive Downtime
When a machine stops due to operator intervention, emergency stop or breakdown, the system prompts the operator for the expected downtime. This is static (breakdown) Productive Downtime. Productive Downtime at any machine is the sum of its dynamic and static Productive Downtimes.
When static downtime is entered, the time is propagated to all other machines on the production line. Since the breakdown machine is expected to be stopped for the given time, all machines benefit. The system monitors MTBF and MTTR and can use this to broadcast estimated downtime without operator intervention.
Productive Downtime is an Advanced Warning
The IPAV System predicts Productive Downtime in four different line states: Sleep, Start-Up, Running and Run-Out. See the posting on Line States for a detailed discussion on how these states are derived.
Many production lines do not have line-of-sight communication between machines. When the line has emptied of product for example, i.e. Run-Out and gone to a Sleep state, each operator has an indicator showing when product is expected to arrive when it restarts. Depending on the line configuration, this could be an hour or more from the first machine starting to run, to product arriving at the last. Operators can use this time more effectively than if they had inaccurate or no knowledge of the state of the production line.
IPAV Systems Equipment and Installation
IPAV Systems equipment at each point-of-interest consists of a Heartbeat device which gathers all sensor signals and a Predictor which displays Productive Downtime to the operator.
The line manager has the option of a Globe device which gathers data from the Predictors and displays a summary of the current state of the line. The Globe has an Ethernet connection and serves up web-pages to any desktop PC browser.
Using the Globe's Ethernet connection, the GlobeLive cross-platform desktop application, supplied free of charge, provides detailed graphical analysis, monitoring and visualisation of the production-line in real-time. A truly powerful tool.
Installation of the IPAV System is simple and non-invasive. Each point requires power and sensors to count product entering and leaving the machine. Communication between Predictors uses robust proprietary wireless adapted for industrial environments.
The IPAV System incorporates many features beyond the scope of this article.