UNIVERSITY OF BOLTON SCHOOL OF ENGINEERING MSC SYSTEMS ENGINEERING AND ENGINEERING MANAGEMENT SEMESTER 2 EXAMINATION 2015/20016

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1 TW63 UNIVERSITY OF BOLTON SCHOOL OF ENGINEERING MSC SYSTEMS ENGINEERING AND ENGINEERING MANAGEMENT SEMESTER 2 EXAMINATION 2015/20016 MONITORING OF MECHANICAL SYSTEMS MODULE NO: EEM7018 Date: Thursday 19 May 2016 Time: INSTRUCTIONS TO CANDIDATES: There are 4 questions. Answer any 3 questions. All questions carry equal marks. Marks for parts of questions are shown in brackets. This examination paper carries a total of 100 marks. All working must be shown. A numerical solution to a question obtained by programming an electronic calculator will not be accepted. The typical properties of piezo film is given at the end of the paper in Table 1.

2 Page 2 of 8 Q1. (a) ATZ is a mechanical engineering company. Recently the senior management team intends to introduce the lean manufacturing into their company. Having analysed the external best practise, they found that the TPM would be one of the key areas for success. An assembly machine has been chosen as a pilot project. You are asked by the management to investigate the effectiveness of the system. On inspecting data collected during one-week operation, you find out the following facts: The assembly machine worked a total of 40 hours over 5 days. Everyday operators have 1-hour lunch breaks. The standard time for the assembly process is 2.5 minutes. After assembling 150 parts, the tool needs to be checked and changed if necessary. 150 minutes required for each time. 8 defective parts have been detected. Detailed data was recorded on each failure and presented in Table Q1(a) The total assemblies made in the week were 380. Table Q1(a) Failure No. Production day/time machine reported down Production day/time machine handed back to production :30 am 02 13:00 am :15 pm 04 10:00 am :00 pm 05 2:15 pm (i) Describing the procedure clearly, estimate the Availability, Performance Efficiency, Rate of Quality Products, and the Overall Equipment Effectiveness. (12 marks) Question 1 continued Please turn the page

3 Page 3 of 8 Question 1 continued (ii) (b) Based on the information obtained from above investigation, comment on the performance of the assemble machine and recommend to the management about adopting TPM. (6 marks) Specify, with the aid of simple block diagrams, the basic elements of a modern Machine Predictive system. Critically explain their principles and functions within the Machine Predictive system. (8 marks) (c) Explain how the vibration analysis can be used as a predictive maintenance tool in machines and equipment. (7 marks) Total 33 marks Q2. (a) Define the: Preventive Maintenance and Predictive Maintenance. (6 marks) (b) Critically discuss Preventive and Predictive Maintenances features. (6 marks) (c) Critically explain the techniques for enhancing maintenance. (6 marks) (d) For a CNC milling machine, the MTBF is normally distributed with a mean of 5,000 hours and a standard deviation of 600 hours. The loss and downtime costs associated with the CNC machine failure are estimated to be 1,000 per failure. It costs 250 to perform the preventive maintenance. You are asked to determine whether a preventive maintenance programme is worthwhile. If the probabilities of failure are 0.03 and 0.4 respectively, what are your recommendations? Assume 200 weeks period, 5 days per week and 16 hours per day. (15 marks) Total 33 marks Please turn the page

4 Page 4 of 8 Q3 (a) Describe the properties of piezo film. (7 marks) (b) Draw a diagram of the equivalent circuit of a piezo film sensor. Describe the electrical properties of this model. (8 marks) (c) A 1.45 psi load is applied to a piezo film switch of 2.54 cm length, 2.54 cm width, and 110μm in film thickness. The force acts on the cross sectional area (the film is being stretched). Calculate the voltage developed across the piezo film. The typical properties of piezo film are given in Table 1 at the back of this paper, and the conversion from psi to N/m2 is approximately 7,000. (8 marks) (d) Two types of amplifiers are commonly used to interface to piezo film sensors, charge amplifier, and a non-inverting amplifier. Describe using a circuit diagram these two amplifiers. (10 marks) Total 33 marks Q4 (a) Explain using a diagram how the characteristics of a filter are specified. (10 marks) (b) A digital filter has the following difference equation: y n = (x n + x n-1 + x n-2 ) / 3 i) What type of filter is described by the difference equation? ii) What is the order of the filter? iii) What are the filter coefficients? iv) What is the transfer function of the filter? (4 marks)

5 Page 5 of 8 Question 4 continued Please turn the page Question 4 continued (c) Explain the term aliasing. (5 marks) (d) Spectral analysis is to be performed on a signal captured from a vibrating machine. The signal has been bandlimited to 0 to 100Hz. The analysis requires a frequency resolution of 0.2 Hz. Determine: i) The required minimum sampling frequency ii) The maximum frequency that can be obtained from the spectrum iii) The number of samples required to compute the spectrum iv) The width of the required time window. Total 33 marks END OF QUESTIONS

6 Page 6 of 8 Appendix Table 1. Typical properties of piezo film Symbol Parameter PVDF Copolymer Units t Thickness 9, 28, 52, 110 <1 to 1200 µm (micron, 10-6 ) d m/m C/m Piezo Strain Constant or 2 d V/m N/m g V/m m/m Piezo Stress constant or g N/m 2 C/m k 31 Electromechanical 12% 20% k Coupling Factor t 14% 25-29% C Capacitance 380 for 28µm 68 for 100µm pf/cm 1KHz Y Young s Modulus N/m 2 V 0 Speed of Sound stretch: thickness: m/s p Pyroelectric Coefficient C/m 2 bk ε Permittivity F/m ε/ε 0 Relative Permittivity ρ m Mass Density kg/m ρ e Volume Resistivity >10 13 >10 14 Ohm meters R œ <3.0 <3.0 Ohms/square for NiAl Surface Metallization R Resistivity œ Ohms/square for Ag Ink tan δ e Loss Tangent KHz Yield Strength N/m 2 (stretch axis) Temperature Range -40 to to bc Water Absorption <0.02 <0.02 % H 2 O Maximum Operating Voltage 750 (30) 750 (30) V/mil(V/µm), 25bC Breakdown Voltage 2000 (80) 2000 (80) V/mil(V/µm), 25bC

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