拋光機(jī)設(shè)計(jì)

拋光機(jī)設(shè)計(jì),拋光機(jī)設(shè)計(jì),拋光機(jī),設(shè)計(jì) Ultrasonic cutting is widely used in food processing applications to produce a clean and accurate cut. However, it is yet to be adopted as an instrument of choice in orthopaedic applications, mainly due to the high temperatures that can be generated at the cut site and the Bone cutting instruments, such as burs, saws and chisels, devices dating back to 1957 2. However, limitations in tool and transducer design and the lack of suitable methods for fine-tuning power control, considerably restricted the years, following improvements in transducer design and the development of more sophisticated electromechanical additional problems of cross-contamination. This study investigates opportunities for controlling the cutting tem- perature, by studying the eects of cutting parameters and cutting blade geometry on cutting temperature, with the aim of designing an ultrasonic cutting device capable of deep cuts in bone without the need for a cooling system. * Corresponding author. Fax: +44 (0) 141 330 4343. E-mail address: m.lucasmech.gla.ac.uk (M. Lucas). Ultrasonics 44 (2006) oer limited precision and manoeuvrability to surgeons 1 and often result in tissue burning, formation of debris and damage of adjacent tissue. An alternative bone cutting device is an ultrasonic blade, Fig. 1(a), which is tuned to a longitudinal vibration mode at a frequency in the low ultrasonic range (20100 kHz). The reported benefits of ultrasonic cutting of hard tissue include elimination of swarf, reduced reaction forces and a more accurate cut. Ultrasonic osteotomy is not a novel concept, with power control, interest has been renewed in ultrasonic sur- gical devices 3. The current challenge for ultrasonic bone cutting resides in the development of tuned systems capable of delivering sucient acoustic power to cut hard tissue without exceed- ing the temperature of bone necrosis. To overcome the problem of tissue burning, ultrasonic cutting devices usu- ally need to incorporate cooling systems, which deliver water (or saline solution) to the cut site 3,4, but this oers consequent requirement to use additional cooling. For example, if cutting temperatures above 5560 C176C are reached, particularly for sus- tained periods, bone necrosis can occur, compromising post-operative recovery. A recent study by the authors has shown that the thermal response in natural materials, such as wood and bone, is aected by the absorption of ultrasonic energy and conduction of heat from the cut site. In this paper the dependency of cutting parameters, such as blade tip vibration velocity, applied load, tuned frequency and coupling contact conditions, on the thermal response are reported and results show that it is possible to maintain cutting temperatures within safety limits by controlling the cutting parameters. A novel cutting blade design is proposed that reduces frictional heat generated at the cut site. Through a series of experimental investigations using fresh bovine femur it is demonstrated that the cutting temperature, and hence thermal damage, can be reduced by selecting appropriate cutting parameters and blade profile. C211 2006 Elsevier B.V. All rights reserved. Keywords: Ultrasonic bone cutting; Temperature; Experimental modal analysis; Modal coupling 1. Introduction early development of the technology. In the last fifteen Methods for reducing in ultrasonic cutting Andrea Cardoni, Alan MacBeath, Department of Mechanical Engineering, University Available online Abstract 0041-624X/$ - see front matter C211 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ultras.2006.06.046 cutting temperature of bone Margaret Lucas * of Glasgow, Glasgow G12 8QQ, UK 30 June 2006 e37e42 response e38 A. Cardoni et al. / Ultrasonics 44 (2006) e37e42 2. Thermal response characteristics during ultrasonic cutting Previous work by the authors has shown that the ther- mal response, measured during ultrasonic cutting of a vari- ety of materials, exhibited two temperature peaks 5,6. Fig. 1(b) shows a typical thermal response measured in bovine femur specimens. Qualitatively similar responses were measured in artificial bone and several grades of wood. The first sharp temperature peak in the measured response occurs due to the absorption of the ultrasonic energy generated by the blade vibration in the material sample during cut initiation. The temperature peak magni- tude increases with increased static load applied to the blade, because increasing the static load improves coupling between the blade and material. The temporal response is independent of the location of the measurement sensor in the specimen 4. The second peak in temperature in the measured response occurs due to heat conduction generated by fric- tion between the blade and specimen as the blade pene- Fig. 1. (a) Schematic of an ultrasonic cutting system, and (b) temperature loads. trates the material, resulting in a gradual increase then decay in temperature during the measurement period. In this case, the temporal response depends on the location Fig. 2. Sketch of 35 kHz (short) and 19.5 kHz (long) ultrasonic cutting blades indented cutting edge section (profile 2). of the sensor in the specimen. For the same cutting depth, the peak conduction temperature measured in the response decreases with increasing applied static load, mainly because the cut occurs more quickly. 3. Influence of blade design on temperature Four titanium alloy ultrasonic cutting blades tuned to resonate longitudinally at two distinct frequencies were designed and manufactured for the present study (Fig. 2). The dimensions of the blades were determined using finite element analysis (FEA). Two blades were tuned at 19.5 kHz and two at 35 kHz. Although dierent lengths were required to tune the blades, the vibration amplitude gain was kept constant and the cutting profile was consis- tent for each blade design. Previous cutting experiments revealed that the sample temperature associated with ultrasonic energy absorption could reach elevated peaks, well above thetemperaturenor- mally quoted for bone necrosis. However, it is known that the necrosis temperature is not a constant and depends on measured in bovine bone during ultrasonic cutting at dierent static the duration for which bone experiences the elevated tem- perature. In fact, bone can withstand higher temperatures without thermal damage if the duration is very short 7. with (a), (b) constant cutting edge section (profile 1) and (c), (d) with The experiments also showed that frictional heat gener- ated during cutting exposed bone samples to prolonged intervalsofhightemperature. This study aims toinvestigate the eect of blade profile on this cutting temperature during ultrasonic cutting of bone and, in particular, the impact of blade geometries with dierent areas of contact between thebladeandthebone.Therefore,twodierentcuttingedge profiles, one with a constant section and a sharp tip (blade profile1),andtheotherwithanindentedprofileterminating in an identical tip (blade profile 2), were incorporated in the tuned blades for each selected frequency (Fig. 2). 3.1. Experimental rig The experimental rig designed to cut bovine femur bone samples is shown in Fig. 3(a). Samples were cut and clamped onto a metal plate attached to a horizontal guide. The transducer and blade assembly was mounted on a sli- der, which was free to travel along the guide. In order to investigate the eects of the applied static force, a system of a pulley, cable and weights was connected to one side of the slider. The depth of each cut was monitored using a dial gauge. Temperature measurements were conducted using six thermocouples distributed in two rows of three, placed on opposite sides of the cutting line, as depicted in Fig. 3(b). The three thermocouples in each row were placed at dis- imen. Probes 13 and probes 46 were positioned 1 and 2 mm from the line of cut, respectively. 3.2. Eects of cutting edge profile, tuned frequency and vibration amplitude on specimen temperature Firstly, cutting experiments used the pair of blades tuned to 35 kHz. The ultrasonic amplitude was set to 23 lm for both blade configurations (profiles 1 and 2), and tests were performed at a series of applied static loads in the range 2075 N. For each cutting experiment, the temperature of the sample was monitored for 300 seconds, to allow the specimen to cool back to room temperature, independent of the cutting time. In Fig. 4 the responses detected by the six thermocou- ples positioned in the bone specimens, being cut using 35 kHz blades with profiles 1 and 2 and with an applied load of 20 N, are shown. It is clear that significantly lower temperatures are recorded by all the probes when cutting with the blade with the indented profile (profile 2) as shown in Fig. 4(b) and, in particular, a peak temperature 40 C176C lower was detected by probe 1. These improved thermal conditions stem from the reduction in the frictional contact area between the blade and specimen during cutting. This also results in a faster cut and facilitates the removal of bone debris from the cut site. As a result, debris combustion through frictional A. Cardoni et al. / Ultrasonics 44 (2006) e37e42 e39 tances of 5, 10 and 15 mm from the top surface of the spec- Fig. 3. (a) Test rig for ultrasonic cutting experiments Fig. 4. Temperature responses measured in bone at six thermocouple locations heating, which was previously cited as a key cause of tissue and (b) thermocouple locations in specimen. using two 35 kHz blades with (a) blade profile 1 and (b) blade profile 2. the tuned 19.5 kHz blade with profile 2, showed signs of poorer than expected cutting performance which could provide an explanation for the dierences between the 35 and 19.5 kHz blades in terms of cutting temperature. Therefore, a study of the vibration characteristics of the 19.5 kHz blade with profile 2 was carried out. 4.1. Linear and nonlinear modal coupling The vibration characteristics were determined via exper- Fig. 6. Dierence in peak cutting temperature between blade profile 1 and profile 2 versus static load measured using the 19.5 kHz blade and tip amplitude of 40 lm. e40 A. Cardoni et al. / Ultrasonics 44 (2006) e37e42 damage, could be reduced 5,6. The eects of applied static load on temperature, using blade profiles 1 and 2, are shown in Fig. 5 for blade tip amplitudes of 23 lm and 40 lm. In the figure, the dierence in peak cutting temper- ature recorded between blade profile 1 and blade profile 2, is plotted against the applied static load. The measure- ments consistently recorded a reduction in the peak tem- perature when using blade profile 2. A small number of deviations from this trend appear due to slight inaccuracies in positioning of the probes. The same experiments were conducted using the 19.5 kHz blade pair to investigate any frequency depen- dency of cutting temperature. Both blades operated at a vibration amplitude of 40 lm, giving the same blade tip vibration velocity as the 35 kHz blades operating at 23 lm. In previous studies, vibration velocity has been demonstrated to be the influencing vibration parameter in ultrasonic cutting experiments 6. By comparing Fig. 6 with Fig. 5(a) it is seen that the measured temperature dierences between profile 1 and profile 2 are much smaller than for the 35 kHz blades and, therefore, at 19.5 kHz the peak cutting temperature is not so dependant on the cutting edge profile for the same blade tip vibration velocity. Again, at 19.5 kHz, the blade with profile 2 cuts faster than the blade with profile 1. Fig. 5. Dierence in peak cutting temperature between blade profile 1 and profile (a) 23 lm and (b) 40 lm. 4. Blade redesign for improved vibration performance Although the cutting blades have been tuned in a longi- tudinal mode, it has been shown previously that cutting performance is critically dependent on the vibration char- acteristics of the tuned blade. In this case, it was found that Fig. 7. Tuned longitudinal mode determined 2, both at 35 kHz, versus static load at blade tip vibration amplitudes of imental modal analysis (EMA) using a 3D laser Doppler vibrometer (LDV) and LMS modal analysis software. Fig. 7(a) shows a side view of the measured tuned mode shape, which reveals a significant flexural contribution to the longitudinal mode of the blade. Fig. 8(b) shows the flexural mode that occurs at a resonant frequency very by (a) EMA and (b) FEA. ear and nonlinear modal interactions. Such energy leakages could have an influence on the thermal response during cutting and, hence, a redesign is proposed to eliminate these eects. The requirements were to uncouple the longi- tudinal mode from the untuned flexural and torsional Fig. 8. EMA modal data for the (a) coupled longitudinal-bending mode and (b) bending mode. A. Cardoni et al. / Ultrasonics 44 (2006) e37e42 e41 close to the longitudinal mode frequency and is the cause of the modal coupling at the tuned frequency. Moreover, when the device was driven at the tuned fre- Fig. 9. Frequency response for system driven at 19.5 kHz in tuned longitudinal mode. quency, a large amount of energy leaked into an internal modal response at half the tuned frequency, which is char- acteristic of a principal parametric resonance 8, Fig. 9. The internally excited mode corresponded to a blade tor- sional mode occurring at 9.9 kHz, shown in Fig. 10. 4.2. Improving blade tuned responses via profile alteration The vibration measurements have illustrated that the response of the 19.5 kHz blade is characterised by both lin- Fig. 10. The internal torsional mode determin Fig. 11. Top view of: (a) the original 19.5 kHz blade with indented cutting edge width profile (blade profile 3). modes without altering the blade length and maintain suf- ficient amplitude gain in the blade profile to allow the blade to operate at the required tip vibration amplitudes 9,10. Two indents were incorporated to alter the width of the blade, as shown in Fig. 11(b) (blade profile 3). EMA of the new blade measured a significant shift in the flexural mode frequency, that uncoupled the flexural mode response from the tuned longitudinal mode response. Also, the indented width profile significantly aected the modal frequency of the torsional mode, achieving a frequency reduction of 1.1 kHz, with the result that the nonlinear modal coupling was also eliminated. The response of the modified blade exhibited a linear single frequency response for blade tip amplitudes up to 55 lm. 5. Eect of blade profile 3 on temperature Further cutting temperature measurements were carried out using the 19.5 kHz blade with blade profile 3 at 40 lm blade tip vibration amplitude. Fig. 12 shows the dierence in peak cutting temperature between the 19.5 kHz blades with profiles 1 and 3, for increasing static load. Despite the improvement in cutting speed due to the new design of profile 3, and the elimination of modal interactions in ed by (a) EMA and (b) FEA. (blade profile 2), and (b) the redesigned blade with additional indented blade profile Table 1 Cutting speed of the blades measured in bone specimens for two ultrasonic Static load (N) Cutting speed of 35 kHz blades (mm/s) l/s Amplitude blade profile 1 l/s Amplitude blade profile 2 25 lm40lm25lm40lm4 20 0.29 0.77 0.49 0.94 -20 0 20 40 60 20 40 60 80 Load (N) Temperature diff. (Deg C) 1 2 3 4 5 6 ab Fig. 12. Dierence in peak cutting temperature between blade profile 1 and (b) 55 lm. e42 A. Cardoni et al. / Ultrasonic the vibration characteristics as an influencing factor in the experiments, no significant temperature reductions could be achieved using this blade design. At a higher ultrasonic amplitude, of 55 lm, improved temperature reductions were recorded in the specimens. The results suggest that at 19.5 kHz, the influence of the cutting edge configuration on temperatures is more significant at higher ultrasonic amplitudes (see Table 1). 6. Conclusions The eect of blade profile on the cutting temperature has been studied in order to investigate ways of controlling the temperature in bone during ultrasonic cutting. The results show that a reduction in the contact area between the blade and specimen reduces sample temperatures during cutting. In particular, at the higher tuned frequency, the indented cutting edge profile has proved to provide consistent reduc- tions in cutting temperature for the range of static loads and two blade tip vibration amplitudes tested. However, at the lower tuned frequency, significant temperature reductions have only been achieved at the higher tip vibra- tion amplitude. The impact of the blade vibration charac- teristics on blade responses was highlighted and it was shown how blade profile alterations could eliminate linear and nonlinear modal interactions, thus removing these as influences in the cutting experiments. 35 0.38 1.27 0.53 1.55 50 0.64 1.60 1.60 4.17 62 0.85 2.24 1.56 4.41 75 1.13 2.54 2.14 5.36 tip amplitudes Cutting speed of 20 kHz blades (mm/s) l/s Amplitude blade profile 2 l/s Amplitude blade profile 2 l/s Amplitude blade profile 3 0lm70lm40lm40lm 0.20 0.71 0.21 0.27 -20 0 20 40 60 20 40 60 80 Load (N) Temperature diff. (Deg C) 1 2 3 4 5 6 3 versus static load, at 19.5 kHz and tip amplitudes of: (a) 40 lm and s 44 (2006) e37e42 References 1 J.Y. Giraud, S. Villemin, R. Darmana, J.Ph. Cahuzac, A. Autefage, J.P. Morucci, Bone cutting, INSERM, Centre Hospitalier Hotel- Dieu, Toulouse, France, 1, 1991. 2 A.G. Nielson, J.R. Richards, R.B. Walcott, Ultrasonic dental cutting instrument, Int. J. Am. Dental Assoc. 50 (1957) 392. 3 T. 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