A conceptual design application based on a generalized algorithm part I. Generation of solving structural variants.

Neagoe, Mircea ; Diaconescu, Dorin ; Jaliu, Codruta 等

1. INTRODUCTION

Based on the analysis of the literature, regarding product conceptual design, a generalized modeling algorithm is proposed by authors in a recent paper (Diaconescu et al., 2008). This paper exemplifies (in two parts) an application of this algorithm on a product of motor-reducer type, which consists of a planetary speed reducer and an electric motor. This motor-reducer is used in a rotational platform on which a parabolic antenna is installed; the motor-reducer must drive the platform in different angular positions, under imposed conditions of accuracy and stability. The first steps of the algorithm up to the generation of solving structural variants inclusive are approached in this paper.

2. ON THE REQUIREMENTS LIST

The following requirements (main objectives) regarding the motor-reducer come out from the requirements list (of the global product formed by the parabolic antenna assembly:

(1) The stable maintenance of the platform angular position: the transmission must be blocked when the motor is disconnected.

(2) The energy source: electrical.

(3) The reducer must be a simple planetary gear with a kinematical transmission ratio: [absolute value of i] = 100 [+ or -] 1.5%.

(4) The reducer admissible minimum efficiency: [[eta].sub.min] = 0.4 (the motor torque must be amplified at least [[eta].sub.min] x [absolute value of i] = 40 times).

Four optimization objectives are associated regarding the minimization of: A. production costs, B. friction losses, C. radial size and D. axial size. These (secondary) objectives are used as evaluation criteria and have the following relative weights: A [approximately equal to] 4B [approximately equal to] 6C [approximately equal to] 8D.

3. MOTOR-REDUCER GLOBAL FUNCTION

The motor-reducer global function is a sub-function of the platform globalfunction; its VDI symbolical structure (VDI, 1997), illustrated in Fig. 1, contains the following sub-functions: M1: Connecting the material (platform) to the mechanical energy; M2: The material angular displacing; M3: Registration of the material angular position; E1: Voltage connecting / disconnecting; E2: Transformation of the electrical energy into mechanical energy + transmission blocking while the motor is disconnected + the speed primary reducing; E3: Transmission of mechanical energy with a new speed reducing; E4: Ramification of the mechanical energy into: useful energy and lost energy; I1: Ramification of the input information into: emission of the starting signal and transmission of the information regarding the desired angular position; I2: Commanding the execution of the starting and stopping signals; I3: Reception of the information regarding the angular positions: desired and actual values and their comparison; I4: Emission of the stopping signal when the actual and desired positions become equal.

The E2 sub-function (Fig.1), which designates the motor-reducer global function, is illustrated separately in Fig. 2,a.

4. MOTOR-REDUCER FUNCTION DETAILING

The structure of the motor-reducer function, illustrated in a VDI symbolic variant in Fig. 2,b, contains the sub-functions: E21: Transformation of the electrical energy into mechanical energy; E22: Movement blocking while the motor is disconnected; E23: Modification of the mechanical energy parameters: speed reducing and torque amplification; E24: Transmission of the mechanical energy (unchanged) between the satellite-gear and central shaft.

The motor-reducer's solving structures will be generated based on the structure from Fig. 2,b; this stage contains: 1) generation of the solving structural variants and 2) establishment of the solving structures, by the kinematical configuration (synthesis) of the obtained variants and by the elimination of the variants whose technical characteristics don't fulfill quantitatively the requirements list.

5. SOLVING STRUCTURAL VARIANTS GENERATION

From the research on the sources of existent solutions, as catalogues of physical effects, catalogues of usual functions solutions, prospects, patents etc. (Cross, 1994; Dieter, 2000; Pahl & Beitz, 1995; Ulrich & Epinger, 1995), were obtained following conclusions regarding the sub-functions E21, ..., E24: 1) All these sub-functions are of KSP (Known Solving Principles) type; 2) The potential principle solutions of subfunctions are entirely known in the effects plan and are partially known in the plan of the effects carriers' configuration (a part of the found configurations can be reconfigured).

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

For exemplification, the results that were found are systematized in the simplified morphological matrix from Fig. 2,c. The product solving structural variants can be generated as compatible combinations between the partial solutions from Fig. 2,c; for example, 6 distinct structural variants were illustrated in Fig. 2,d: SR1, ..., SR6.

6. CONCLUSIONS

The previous obtained variants (Fig. 2,d) fulfill the requirements list qualitatively certainly and quantitatively uncertainly; thus, from these variants, there will be considered as solving structures (of the motor-reducer function: E2) only those whose technical characteristics fulfill the requirements list both qualitatively and quantitatively.

The qualitative schemes of the six variants from Fig. 2,d are represented in a simplified way (without representing the motor) in Fig.3. For these schemes, the second part of the paper will establish the main technical performances: the numbers of teeth (from [absolute value of i] = 100 [+ or -] 1.5 %) and then, the efficiency and the torque amplification ratio.

[FIGURE 3 OMITTED]

The solving structures of the function E2 will be nominated by the variants that block the transmission when the motor is disconnected and accomplish the requirements: [absolute value of i] = 100 [+ or -] 1.5 % and [eta] [greater than or equal to] 0.4; then, by technical and economical evaluation will be established the product concept.

7. REFERENCES

Cross, N. (1994). Engineering Design Methods, J. Wiley & Sons, ISBN 0-4719-4228-6, New York

Diaconescu, D. et al. (2008). On a Generalized Algorithm of the Technical Product Conceptual Design, The 19th International DAAAM SYMPOSIUM "Intelligent Manufacturing & Automation: Focus on Next Generation of Intelligent Systems and Solutions", 22-25th October 2008 (accepted paper)

Dieter, G. (2000). Engineering Design, McGraw Hill, ISBN 007-116204-6, Boston

Pahl, G. & Beitz, W. (1995). Engineering Design, Springer, ISBN 3540504427, London

Ulrich, K. & Epinger, S. (1995). Product Design and Development, McGraw-Hill Inc. ISBN 0-07-113742-4, New York

Verein Deutscher Ingenieure V.D.I (1997). Richtlinien 2221 and 2222