**3.2 Meta-action and meta-action unit**

### *3.2.1 Meta-action*

are represented as well. Also, the use of meta-action reliability technology is described in this section, to provide references for increasing CNC machine tools' degree of reliability. The applications are introduced in three aspects: reliability

The "FMA" structured decomposition is used to decompose the CNC machine tool to the meta-action level and carry out the reliability analysis at the MU level. One may conduct the "FMA"-structured decomposition as shown in **Figure 1**. The concrete steps of the meta-action decomposition method are described as follows:

1. Analyze all functions of the CNC machine tool by means of its design project

3. Analyze the transfer route from the power part to the actuator(s) and obtain

4.Depict the FMA tree including functions, movements, and meta-actions based

• Function layer: it is the design function of the CNC machine tool at the level of design, i.e., milling, grinding, drilling, and turning functions.

• Motion layer: in order to ensure the normal implementation of a function, the required motion combination level is the motion layer. For example, in order to realize the function of "drilling" in a machining center, it is necessary to co-ordinate the movement of spindle rotation, the indexing

5. Determine the elements to realize the meta-action and describe the MUs

of NC turntable, X-Y-Z axes, which form the motion layer

2. According to the structure of the CNC machine tool, study the pattern to realize the function and determine the movements facilitating certain

modeling, design, and manufacturing.

*Reliability and Maintenance - An Overview of Cases*

description or instruction manual.

**3.1 FMA decomposition method**

*FMA-structured decomposition.*

functions

**50**

**Figure 1.**

the meta-actions.

on the above three steps

The function of a CNC machine tool is accomplished by motion, which in turn is usually done by a transmission system. The latter can be decomposed into the most basic motion unit. Therefore, meta-action may be defined the smallest motion in mechanical products.

The meta-action of CNC machine tool can be usually divided into moving metaaction and rotating meta-action. The former realizes the most basic moving functions, such as the linear movement of piston in the cylinder, the linear movement of a nut along the axis of a screw, the movement of a moving guide rail on the static guide rail, etc.

The latter accomplishes the most basic rotating functions, such as a pair of gear transmission that may be divided into two gear rotating meta-actions. A pair of worm and gear transmission can be decomposed into worm rotating meta-action and worm wheel rotating meta-action.

In design and manufacture, the performance of a CNC machine tool can be controlled only by managing the performance of meta-action.

#### *3.2.2 Meta-action unit*

In order to realize the movement of components, the following four elements must be present:


For example, in order to carry out the rotational motion function of the spindle, it is necessary to have a motor coupling, a pulley, or a gear as the power input, an intermediate drive shaft and a gear as the transmission parts, a supporting part (such as a spindle box) for mounting the transmission parts, and a spindle body as the motion output. These parts form an assembly that facilitates the rotation movement function of the main shaft.

In view of the above, one might define the MU as the unified whole of all parts, which can ensure the normal operation of the meta-action according to the structural relations. The MU must have the following basic elements: power input, power output, middleware, support, and fastener. The specific definition of each basic element is shown in **Table 1**.

*3.2.3 The basic model of MU*

1. The conceptual model of MU

In order to describe the concept of MU, a conceptual MU model is established, which is shown in **Figure 2**.

2. The structural model of a MU

The structural model describes the MU from the aspect of mechanical structure. In general, two types of MUs units are moving units and rotating units. **Figure 3** is


the structural model of typical rotating units. **Figure 4** is the structural model of

*Reliability Technology Based on Meta-Action for CNC Machine Tool*

*DOI: http://dx.doi.org/10.5772/intechopen.85163*

The assembly model of a MU describes the assembly process of a MU. Therefore, it is necessary to establish their standard assembly process according to the structural model of two types of MU, and draw the assembly model diagram according to the standard assembly process. **Figure 5** shows an assembly model

As the smallest action unit in enabling a CNC machine tool's function, MU's reliability affects the whole system [20]. Therefore, the technology incorporated in the MU should be studied and the reliability mathematical model of the MU should

typical moving units.

of a MU.

**53**

**Figure 4.** *Pallet moving MU.*

**Figure 3.** *Worm rotating MU.*

**3.3 Applications**

be established first.

3. The assembly model of MU

*3.3.1 Reliability mathematical modeling based on MU*

#### **Table 1.**

*The definitions of MU basic elements.*

**Figure 2.** *The conceptual MU model.*
