A buffer is a storage for a item. It represents a place where inventory of an item is kept. It’s often called SKU.
Different types of buffers exist:
Fields
Field | Type | Description |
---|---|---|
name | non-empty string | Name of the buffer.
This is the key field and a required attribute.
|
description | string | Free format description. |
category | string | Free format category. |
subcategory | string | Free format subcategory. |
owner | buffer | Buffers can be organized in a hierarchical tree.
This field defines the parent buffer.
No specific planning behavior is currently linked to such
a hierarchy.
|
members | list of buffer | Buffers can be organized in a hierarchical tree.
This field defines a list of child buffers.
|
location | location | Location of the buffer.
Default is null.
The working hours and holidays for the buffer are taken
from the ‘available’ calendar of the location.
|
item | item | Item being stored in the buffer.
Default is null.
|
onhand | double | Inventory level at the start of the time horizon.
Default is 0.
|
carrying_cost | double | The cost of carrying inventory in this buffer.
The value is an annual percentage of the item sales price.
The default value is 0.0.
|
minimum | double | Desired minimum inventory, aka safety stock.
Use this field if the safety stock doesn’t change over
time.
The solver treats this as a soft constraint, ie it tries
to meet this inventory level but will go below the minimum
level if required to meet the demand.
A problem is reported when the inventory drops below this
level.The safety stock target is expressed as a quantity. If
you want to define a safety stock target as a time value
(aka days of inventory), you can set a post-operation time
on the producing operation of the buffer.
|
minimum_calendar | calendar | Refers to a calendar storing the desired minimum inventory
level, aka safety stock.
Use this field when the minimum inventory level is varying
over time. Otherwise use the minimum field. If both fields
are specified, the minimum field is ignored.
|
maximum | double | Refers to a calendar storing the maximum inventory level.
This field is not used by the solver.
A problem is reported when the inventory level is higher
than this limit.
|
maximum_calendar | calendar | Refers to a calendar storing the maximum inventory level.
Use this field when the maximum inventory level is varying
over time. Otherwise use the maximum field. If both fields
are specified, the maximum field is ignored.
|
mininterval | duration | Replenishment batching window.
When multiple replenishments for the buffer are planned
closer than the time window specified in this field, the
solver algorithm will try to combine them into a single
larger replenishment.
The default value of the batching window is -1, which keeps
the batching logic deactivated.
|
producing | operation | This operation will be instantiated by the solver to replenish the buffer with additional material. |
detectproblems | boolean | Set this field to false to supress problem detection on this
buffer.
Default is true.
|
flows | list of flow | Defines material flows consuming from or producing into this buffer. |
flowplans | list of flowplan | This field is populated during an export with the plan results
for this buffer. It shows the complete inventory profile.
The field is export-only.
The description of the flowplan model is included in the
section on operationplan.
|
level | integer | Indication of how upstream/downstream this entity is situated
in the supply chain.
Lower numbers indicate the entity is close to the end item,
while a high number will be shown for components nested deep
in a bill of material.
The field is export-only.
|
cluster | integer | The network of entities can be partitioned in completely
independent parts. This field gives the index for the
partition this entity belongs to.
The field is export-only.
|
hidden | boolean | Marks entities that are considered hidden and are normally not shown to the end user. |
action | A/C/AC/R | Type of action to be executed:
A: Add an new entity, and report an error if the entity
already exists.
C: Change an existing entity, and report an error if the
entity doesn’t exist yet.
AC: Change an entity or create a new one if it doesn’t
exist yet. This is the default.
R: Remove an entity, and report an error if the entity
doesn’t exist.
|
The default buffer uses an “producing” operation to replenish it. No fields are defined in addition to the ones listed above.
A procurement buffer is replenished by a supplier.
A number of parameters control the re-ordering policy: classic re-order point, fixed time ordering, fixed quantity ordering, etc...
The fields LEADTIME, MININVENTORY and MAXINVENTORY define a replenishment with a classical re-orderpoint policy. The inventory profile will show the typical sawtooth shape.
The fields MININTERVAL and MAXINTERVAL put limits on the frequency of replenishments. The inventory profile will have “teeth” of variable size but with a controlled interval.
The fields SIZE_MINIMUM, SIZE_MAXIMUM and SIZE_MULTIPLE put limits on the size of the replenishments. The inventory profile will have “teeth” of controlled size but with variable intervals.
Playing with these parameters allows flexible and smart procurement policies to be modelled.
Note that frePPLe doesn’t include any logic to compute these parameters. The parameters are to be generated externally and frePPLe only executes based on the parameter settings. At a later stage a module to compute these parameters could be added.
The PRODUCING field is unused for this buffer type. Propagation through a bill of material will be stopped at a procurement buffer.
Field | Type | Description |
---|---|---|
leadtime | duration | Time taken between placing the purchase order with the
supplier and the delivery of the material.
When the “LEADTIME” constraint is enabled in the solver,
it won’t create any new procurement orders that would
need to start in the past.
|
fence | duration | Time window (from the current date of the plan) during
which procurement orders are expected to be released.
When the “FENCE” constraint is enabled in the solver, it
won’t create any new operation plans in this time fence.
Only the externally supplied existing procurement plans
will then exist in this time window.
|
mininventory | positive double | Lowest inventory level we’re trying to respect. |
maxinventory | positive double | Inventory level to which we try to replenish.
The actual inventory can exceed this value.
|
mininterval | duration | Minimum time between replenishments.
The order quantity will be increased such that it covers
at least the demand in the minimum interval period. The
actual inventory can exceed the target set by the
mininventory field.
|
maxinterval | duration | Maximum time between replenishments.
The order quantity will replenish to an inventory value
less than the maximum when this maximum interval is
reached.
|
size_minimum | positive double | Minimum quantity for a replenishment.
This parameter can cause the actual inventory to exceed
the target set by the MinimumInventory parameter.
|
size_maximum | positive double | Maximum quantity for a replenishment.
This parameter can cause the maximum inventory target
never to be reached.
|
size_multiple | positive double | All replenishments are rounded up to a multiple of this value. |
An infinite buffer has an infinite supply of the material is available.
The PRODUCING field is unused for this buffer type.
Propagation through a bill of material will be stopped at an infinite buffer.
Example XML structures
Adding or changing a buffer
<plan>
<buffers>
<buffer name="item a @ location b">
<item name="item a" />
<location name="location b" />
<onhand>10</onhand>
</buffer>
</buffers>
</plan>
Update the current inventory information of an existing buffer
<plan>
<buffers>
<buffer name="item a @ location b" onhand="100" action="C" />
</buffers>
</plan>
Deleting a buffer
<plan>
<buffers>
<buffer name="item a @ location b" action="R"/>
</buffers>
</plan>
Example Python code
Adding or changing a buffer
it = frepple.item(name="item a")
loc = frepple.location(name="location b")
buf = frepple.buffer(name="item a @ location b",
onhand=10, item=it, location=loc)
Update the current inventory information of an existing buffer
buf = frepple.buffer(name="item a @ location b",
onhand=10, action="C")
Deleting a buffer
buf = frepple.buffer(name="item a @ location b", action="R")
Iterate over buffers, flows and flowplans
for b in frepple.buffers():
print "Buffer:", b.name, b.description, b.category
for l in b.flows:
print " Flow:", l.operation.name, l.quantity,
l.effective_start, l.effective_end
for l in b.flowplans:
print " Flowplan:", l.operationplan.operation.name,
l.quantity, l.date