John asked: What is the difference between Takt Time and Takt Image?
Takt time is the calculated pace of production based on the average speed at which the customer is buying a product or service. The formula is net available time to produce per time period divided by customer demand per time period.
Net available time = 450 minutes / shift
Customer demand = 150 pieces / shift
Takt time = 3 minutes / piece
You can’t measure takt time with a stop watch, only calculate it. Takt time is not the time it takes to perform a task. Takt time is only reduced or increased by changes in production demand or net available time to work. Takt is a German word for ‘beat’ or ‘rhythm’ and is often likened to an orchestra conductor keeping time.
Takt image on the other hand is any sort of visual way to monitor process performance to takt time. For example we can use a hand-drawn chart, a digital display board, a material delivery trolley that comes around every multiple of takt time, or a signal given off by a machine when a product is completed on-time to takt time.
One of the most common types of takt image is called pitch. When used in the context of conveyance, pitch is also a calculated number. Typically used at the pacemaker process, pitch is calculated as takt time multiplied by the pack out quantity. In other words if the takt time is 3 minutes per piece and the pack out quantity is 10 pieces per container the pitch is 30 minutes per container.
Takt time = 3 minutes / piece
Pack-out quantity = 10 pieces / container
Pitch = 10 pieces x 3 minutes / piece = 30 minutes
Takt image = 30 minutes / container
Every 30 minutes a material handler would arrive to remove the box and also replenish material. Pitch is extremely useful when managing large or bulky items that need to be removed from the line periodically. Pitch also functions as takt image because the filling and removing of a box every 30 minutes is a very visual way of letting you know if you are meeting takt.
Pitch for conveyance is related to but not to be confused with pitch as in “pitch lines” along an assembly line. These lines are typically at or less than takt time increments, although they can be more. These pitch lines are also examples of takt image, but they are different from pack out quantity-based pitch. For example in an automotive assembly line with a takt time of 60 seconds, with a pack out quantity (although you would not really use this term) is 1 vehicle the pitch lines could be every 20 seconds, or less than takt. Typically in a fixed position stop system the pitch lines are before, at and after takt to enable abnormality management visually.
Takt image allows people to sense (ideally see or hear) whether or not they are on time to takt. Thirty minutes may be too long in a high volume operation, in which case pitch may still be used to pace the removal of full containers but other means may be needed to provide the takt image more regularly. A rule of thumb is that pitch should be no more than 2 hours at the most so that performance checks can be made in the process at least every 2 hours. Another point to keep in mind is that relying overly on pitch or takt image based on multiples of takt time can hide waste. The variations between part to part or cycle to cycle can be hidden when they average out to being “on time” at the container or takt image level.