Types of modularity and modules

Ulrich and Eppinger (2000) divide the types of modularity into slot, bus and sectional modularity. Ulrich and Tung (1991) divide slot modularity into three sub-categories which are component swapping, component sharing and fabricate-to-fit modularity. Table 1 shows the different types of modularity presented by Ulrich and Eppinger (2000) and Ulrich and Tung (1991).

Table 1.Types of modularity

Ulrich & Eppinger 2000 Ulrich & Tung 1991 Slot modularity Component swapping modularity

Component sharing modularity

Fabricate-to-fit modularity

Bus modularity Bus modularity Sectional modularity Sectional modularity

Österholm and Tuokko (2001) define the sub-categories of slot modularity as follows:

• Component swapping modularity

o at least two different components can be attached to the same base structure

• Component sharing modularity

o the same component can be used in many different base structures

• Fabricate-to-fit modularity

o one or more standard components are used with a component that can be pa- rametrically varied

According to Salvador et al. (2002), there is one more type of slot modularity which can be derived from the combination of the above sub-categories. They present the concept of combinatorial modularity. This type of modularity uses standard modules that are con- nected to each other by standard interfaces. The main difference is the lack of a certain base machine that is evident in other types of slot modularity. The above types of slot modular- ity are shown in Figure 6.

Figure 6. Slot modularity (Ulrich and Eppinger 2000, Ulrich and Tung 1991, Salvador et al. 2002)

In sectional modularity all the interfaces between the modules are identical and the assem- bly of the product is done by attaching the similar interfaces (Ulrich and Eppinger 2000).

Bus modularity has standardized interfaces between the modules and the bus. The modules are attached to the bus which serves as the base for the product (Ulrich and Eppinger 2000).

Sectional modularity and bus modularity are shown in Figure 7.

Figure 7. Sectional modularity and bus modularity (Ulrich and Eppinger 2000)

Considering configuration Pulkkinen and Bongulielmi (2004) see that modularity

“…enables component swapping in a configuration and component sharing between con- figurations”. Thus, within a configuration the base structure can be varied with different modules to provide different variants whereas commonality can be introduced by sharing these modules between configurations. Note, that all the modules can be predefined and in this sense common, while the different configurations provide the needed variety.

Bus modularity Sectional modularity

Component sharing modularity

Combinatorial modularity Fabricate-to-fit modularity

Component swapping modularity

The types of modules are discussed in detail since modularity and the usefulness of the modules are largely dependent on this issue. Pahl and Beitz (1986) divide modules into functional and structural modules. Structural modules are designed according to the manu- facturing or assembly, thus they can be assembled by connecting the predefined interfaces during the assembly process. Functional modules are defined according to the realization of the technical functions. The functions are obtained by one module or by a set of modules (Pahl and Beitz 1986). The division to functional and structural modules is due to the driv- ers that control the decomposition or integration of the product structures, thus the driver is the production system or the functionalities of the product (Stake 1999). Pahl and Beitz (1986) clarify the types of functions and modules according to Figure 8.

Figure 8. Module types according to the functions (Pahl and Beitz 1986)

According to Lapinleimu (2000), a structural module is a part of the main product and can be handled as an own product itself in production, i.e. a structural module equals the pro-

Possible module Essential module

Only in special cases, leads to mixed systems Function

variant

Basic functions

Auxiliary functions

Special functions

Adaptive functions

Customer spe- cific functions

Basic mo- dules

Auxiliary modules

Special modules

Adaptive modules

Non-module

Implementation Variants Assembly Machine Plant Basic,

recurring, general

Locating, joining

Special, completing, expanding

Not pre- cisely defin- able in all areas

Not predic- table

Mixed system Module system

duction module defined by Pahl and Beitz (1986). Lapinleimu (2000) divides the structure further to basic modules, main modules and sub-modules. The basic modules are the ones that form the actual product. The concept of main modules and sub-modules is needed if multiple layers in the product structure are required. As Lapinleimu (2000) addresses the similarity between the production system and the product structure, Pahl and Beitz (1986) concentrate on defining the modules via the functions that together form the basis for the product to work. The division of the module types into structural and functional modules represents actually the far ends of modularity as mentioned in the previous section. Both of these types of modularity have their own benefits and shortcomings. This is the reason why the types of modularity should be clarified and understood more broadly in order to define the best possible product structure and modularity for the organization. In this thesis the type of modularity is related to type of module i.e. the structural modules provide the basis for structural modularity while functional modules provided the basis for functional modu- larity which represent assembly based modularity and function based modularity respec- tively (see section 2.2.5).