Y3150E型滾齒機的PLC改造設計【說明書+CAD】,說明書+CAD,Y3150E型滾齒機的PLC改造設計【說明書+CAD】,y3150e,型滾齒機,plc,改造,設計,說明書,仿單,cad facturing can be micro-machines (m-machines) and m-devices which are usually characterized by their small size, light weight, high energy-conversionefficiencyand low energyconsumption,quick response, high reliability, low cost, high integration, high intelligence level, etc. Typical examples are m-machine tools, m-robotics, m-aircrafts, m-submarines, m-devices, medical m- instruments, m-satellites, m-gears, m-pumps, m-valves, m-sen- sors, and m-actuators. A common feature to most of the m- machines andm-devices is that their structures are getting more and more complex and are often three-dimensional (3-D) while their sizes are becoming smaller, which imposes a critical challenge to their manufacturing issues. The existing MEMS andLIGAtechnologieshavebeenwidelyusedfor2-Dand2.5-Dm- manufacturing applications, however, they do not provide a capability for 3-D m-manufacturing 2. Therefore, an important bearing is targeted for use in m-manufacturing and precision Fig. 1 shows a schematic view of the rotary flexural bearing which has three bearing sections and is configured as a m-spindle unit. The bearing consists of inner and outer bearing cages, a bearing shaft, and a m-coupling that is connected to a m- servomotor (an external power source). The rotational/oscilla- tional motions of the bearing shaft are guided by the bearing, which is expected to be of extremely high accuracy. The whole design is compact in size without any redundancy. The use of am- coupling can minimize the erroneous torque transmission caused by the possible misalignment between the bearing shaft and the servomotor shaft, as well as vibrations and/or error motions of theservomotor.Inthisway,therotational/oscillationalaccuracyof the bearing can be maintained. 2.1. General design considerations level or better. C15 It should be compact to fit into the limited spaces in various CIRP Annals - Manufacturing Technology 57 (2008) 179182 n m The ized on ch error Contents lists available at ScienceDirect CIRP Annals - Manufacturing metrology, suchasm-EDM 3,m-ECM4, ultrasonicm-machining and challenging research topic has been to designm-machines or m-devices that are capable of 3-D m-manufacturing at the nanometric accuracy level. This study proposes a novel rotary flexural bearing that is capable of achieving rotational/oscillational motions of high accuracy and a design methodology for such a bearing. The The bearing must satisfy the following requirements: C15 It should be able to rotate/oscillatein one complete revolution. It should have sufficient strength and fatigue life for a sustained period of time. C15 It should possess rotational motion accuracy at the nanometer A rotary flexural bearing for micromanu H.P. Luo a , B. Zhang (2) a,b, *, Z.X. Zhou a a Hunan University, Hunan, China b University of Connecticut, CT, USA 1. Introduction Industrial products with small feature sizes are becoming more important. These products are distributed over many industries, including machine tools, automotive, medicine, electronics,optics,pharmaceutics,andcommunications1.They ARTICLE INFO Keywords: Spindle Finite element method Rotary flexural bearing ABSTRACT This study proposes a desig principles of elastic flexures. revolution and is character and no lubrication requirements, From the structural characterist provides a design analysis analysis and calculations (su motion error analysis and journal homepage: http:/ees.el 5, laser m-machining 6, and coordinate measuring machines. The design of the bearing is based on the principle of flexural mechanisms that realizes rotational/oscillational motions of one * Corresponding author. 0007-8506/$ see front matter C223 2008 CIRP. doi:10.1016/j.cirp.2008.03.033 complete revolution through the elastic deformation of the elastic flexures. 2. The proposed rotary flexural bearing ethodology for a novel rotary flexural bearing that is based on the motion bearing is capable of providing rotational oscillations of one complete by potentially high repeatability, smooth motions, no mechanical wear no gapsor interfaces,zero maintenance, in addition to itscompactness. ics and the basic working principles of the flexural bearings, the study the various aspects of the bearing, including material selection, stress as nonlinear finite element analysis, static and fatigue strength designs), reduction strategy, parametric design, etc. C223 2008 CIRP. nested without Technology micro-machines and devices. In the proposed design, the inner and outer bearing cages are and connected at one end (left end in Fig. 1). Although the bearing can be designed as a monolithic structure any joints, the proposed two-piece design is purely based 2.1.4. Multiple bearing sections in series For a complete revolution of rotation, the bearing needs to have at least 3608 angular displacement. It is impossible for a single-section bearing to achieve such a large deflection. This is because too large deflection in a single bearing section could over stress the elastic flexures, resulting in permanent (plastic) deformation or even fracture. Over deflection could also cause the so-called necking and cross interference phenomenon, as demonstrated in Fig. 2. To obtain a large oscillation range without such a problem, the bearing is designed using multiple sections in series. Fig. 2. Necking phenomenon of a bearing section. H.P. Luo et al./CIRP Annals - Manufacturing Technology 57 (2008) 179182180 on the fabrication considerations since the monolithic design would be extremely difficult to fabricate. By axis-symmetrically arranging the elastic flexures in the inner and outer cages, the bearing is flexible in the circumferential direction, but stiff in the other directions. The rotational oscillation of 3608 (one complete revolution) or larger can be obtained. If a larger angular displacement (e.g., 3608) is desirable, more bearing sections can be added to the design although to do so makes the bearing longer and less stiff. Otherwise, the bearing can have a compact and relatively stiff design. It should be pointed out that theoretically, the bearing should be free of motion errors. Practically, it would have motion errors because of various errors involved in the bearing fabrication and assembly processes. Motion errors can also be induced due to material defects in the bearing. The bearing is designed under the following considerations. 2.1.1. Use of straight flexures Compared to the other types of flexures, straight flexures have certain advantages, such as distributed compliance over the whole flexure length rather than lumped compliance localized at certain points under stress conditions. Straight flexures can effectively suppress the stress concentration 7, which in turn provides more compliance and longer fatigue life at the material endurance limit. Furthermore, the straight flexures can be small in thickness but large in other dimensions for high compliance in the rotational direction and high stiffness in the other directions. 2.1.2. Use of axis symmetry Symmetry is a powerful design tool in minimizing or eliminating bearing errors. In this design, the identical elastic flexures are axis-symmetrically arranged and uniformly distrib- uted over the circumference of the bearing, which is expected to help suppress motion errors in the radial, axial and tilt directions. Meanwhile, such a bearing is insensitive to temperature rise in the working environment because errors due to thermal expansion tend to cancel each other. Additionally, the axis-symmetric design can largely simplify the bearing fabrication. It also facilitates an easy compensation for errors due to geometric inaccuracies stemming from the fabrication process, which helps improve Fig. 1. Schematic view of the bearing configured as a m-spindle. the overall performance of the bearing. 2.1.3. Even number of elastic flexures Perfectaxissymmetryofelasticflexuresisimpracticalduetothe fact that there exist geometric errors in the flexural bearing during thefabricationandassemblyprocesses.Anyerrorsinthesymmetric distributionoftheelasticflexuresmayresultinerrormotionsofthe bearing. To minimize the geometric errors in the fabrication and assembly processes, a good strategy is to use an even number of elastic flexures in the bearing design. When the wire electric dischargemachining(WEDM)methodisusedtomachinetheelastic flexures, for example, two opposing flexures can be simultaneously cut. The simultaneous machining of the two opposing flexures not only minimizes the geometric difference between the two flexures, but also relaxes the machining tolerance of the entire bearing. 2.1.5. Nested design of bearing cages The bearing utilizes bending deflections in the circumfer- ential direction to realize its rotational motion. A bearing section will have a decrease in its length if subjected to torsion. The decrease in length can directly contribute to the axial error motion of the bearing. To minimize or eliminate such an error motion, nested design of bearing cages is proposed. In this design, an inner bearing cage is inserted into an outer cage of the similar length and is further connected to the outer bearing cage at one end. If the other end of the outer cage is fixed, the free- end (the right side end in Fig. 3) of the inner bearing cage will have very little or even no axial motion error d r when it is subjected to an external torque. This is because the axial error motion of the inner bearing cage is effectively canceled by that of the outer cage. The nested and axis-symmetric design can effectively cancel the error motions due to thermal expansion of the bearing material. This is because the inner and outer bearingcages would haveauniformexpansioninbothradialandaxialdirectionsifthe bearing should be exposed to a temperature field. Moreover, the nested design not only effectively increases the oscillation range of the bearing, but also reduces its overall dimensions for compactness. Fig.3.Nested design ofouter and innercages effectivelyreduces bearing axialerror d r . C15 C15 static a 1 C16C17 defectsandstressconcentration(fatiguenotchsensitivityor stress concentration sensitivity). For this reason, in the process of the bearing fabrication, the elastic flexures should be machined with a surfaceroughness less than Ra2.5mm and with smooth edges, but no sharp notches or pits. 2.3. Design calculations Strengthisthepriorityforthebearing.Thebearingmustnotfail H.P. Luo et al./CIRP Annals - Manufacturing Technology 57 (2008) 179182 181 M c A 1 E r A 2 s s E a 2 (1) where a 1 and a 2 are dynamic and static performance indicators for materialselection;A 1 andA 2 areweightingfactorsoftherespective dynamic and static performance indicators; E and r are Youngs modulus and mass density of the material, respectively. Using Eq. (1), the comprehensive parameter M c is calculated as 2400 Pa/ (kg/m 3 ) for titanium alloy Ti6Al4V which is compared to 1199 for beryllium copper, and 370 for spring steel. Among the selected bearing materials, titanium alloy is best to use in terms of its comprehensive parameter and endurance limit (700 MPa for titanium alloy as compared to 321 and 490 for beryllium copper and spring steel, respectively). Moreover, this material can achieve a high surface finish and dimensional accuracy when machined with the wire electro-discharge machin- ing method. In addition, titanium alloy has excellent corrosion resistance which is even better than that of stainless steels. Based on the above considerations, titanium alloy has been therefore selected for the bearing. It should be pointed out that although titanium alloy is a material of comprehensive performance, it is sensitive to surface parameter not have aging and creeping problems. In the above considerations for material selection as well as the and dynamic performancesof the material, a comprehensive is introduced for material selection 9, C18C19C20C21C20C21 have a long lifetime under the cyclic loading conditions. Long-term stability. The material should have a long-term stability under various environmental conditions, including the corrosive and elevated temperature environments. It should machine. The machined bearing should possess good surface finish, surface integrity, and dimensional accuracies. High fatigue strength. High fatigue strength allows the bearing to C15 Good bearing must have high elastic modulus combined with low mass density 9. machinability. The bearing material must be easy to C15 High cause error motions. elastic modulus. To have a good dynamic performance, the gravitational 2.1.6. Corner fillet The corner fillet at the connections of the elastic flexures in the individual bearing section should be properly designed to minimize the stress concentration so as to increase the fatigue life of the bearing. In addition to the above considerations, the design of the bearing also includes material selection, strength analysis and calculations (with both static and fatigue considerations), analysis and suppression of error motions in the radial, axial and tilt directions, stiffness analysis and calculations, etc. 2.2. Material selection Since the bearing realizes its rotational/oscillational motions based on the elastic deflections of the circumferentially arranged flexures, it is subjected to cyclic stress conditions. In selecting a materialforthebearing,fatiguestrengthandflexibilityareofprime consideration.Thebearingmustbecompactinsizetominimizethe effect of the gravitational force and to meet the application requirements for m-machines and m-devices. The following con- siderations have been given for the material selection: C15 High static strength. To achieve the maximum possible deflection of the elastic flexures in the bearing, the bearing material should havearatiooftheyieldstrengthtoelasticmodulus(s s /E)aslarge as possible 8. This is considered the most important material requirement. C15 Lowmaterialdensityr.Thedensityofthebearingmaterialshould be as low as possible to minimize the deflection to the force which could bend the bearing axis and thus during its cyclic rotations/oscillations. Stress analysis needs to be performedandthedetailedstressestobecalculatedforthebearing structure. Inthedesigncalculations,finiteelementmethod(FEM)wasused onasinglebearingsectionfortherespectiveinnerandouterbearing cages which were formed by the serial connection of the individual bearing sections. In this way, the amount of work in the FEM calculationswassignificantlyreducedasopposedtothecalculations of the entire bearing. Fig. 4 shows an individual bearing section subjectedtobothclockwiseandcounter-clockwiserotations.Stress distributions of and the maximum stress points within the bearing sectionwerethusobtainedinthiswayintheFEMprocess.Whenthe bearing section is deformed by a torque, the elastic flexures of the bearing are deformed due to the combined bending and twisting effects. Because the elastic flexures are radially confined at the connection portion and distributed in the circumferential direction ofthe bearingcage, theycannothaveend rotation or warping.They can be subjected to tension, twisting, and bending, and are thus in the three-directional stress state. 2.4. Nonlinear finite element analysis Since the flexural bearing undergoes large deformations during a working process, the problem becomes geometrically nonlinear even though the actual strain may be small and is well within the elastic limit. In this study, ANSYS9.0 was adopted in the FEM calculations of the bearing. Displacement (angular in this study) loading method was used in the calculations. In the nonlinear deformation problems, the displacement loading method usually speeds up the calculations. 2.5. Analysis and minimization of axial error The axial error of the flexural bearing comes from two different sources. The first and also major axial error source is due to the elastic motions of the bearing. When a bearing section is given an angular displacement, it has a reduction in its length. As the entire bearing is given an angular displacement, both inner and outer cages have reductions in their respective lengths. Although the lengthreductionsofthetwocagescanceleachotherbecauseofthe coupling effect of the bearing cages, if the cancellation does not come to zero, an axial error motion occurs. Fortunately, such an axial error motion can be minimized or even eliminated by carefully designing the inner and outer bearing cages so that both cages have the same length reduction under external load conditions. The second and also minor axial error source results from the tilterrormotion.Anytilterrormotion,ifprojectedtotheaxisofthe bearing, causes the bearing to have axial error motion, although such an effect is secondary and negligible. Fig. 5 shows an FEM result of axial error motion of nested single inner/outer bearing Fig. 4. Individual bearing section subjected to clockwise and counterclockwise rotations. H.P. Luo et al./CIRP Annals - Manufacturing Technology 57 (2008) 179182182 sections subjected to the external torque conditions. Due to the geometrically nonlinear phenomenon, the axial error motion is nonlinear in terms of the applied torque. 2.6. Fatigue analysis and design Because the bearing is subjected to cyclic stress conditions, the fatigue problem must be taken into consideration at the design stage in order for the bearing to have a long lifetime. When titanium alloy is used for the bearing, its SN curve (or Wohler curve)hasanendurancelimitbelowwhichthematerialneverfails under cyclic loading conditions. The design used the endurance limit of the material with the fatigue safety factor larger than the allowable fatigue safety factor. The stress level of the bearing is proportional to its angular displacement. The highest stress level is expected when the bearing reaches its maximum angular displacement. The elastic flexures in the bearing are subjected to asymmetrically cyclic and tri-axial complex stress conditions. Under the conditions of uni- axial, constant amplitude and asymmetrical cyclic stress, fatigue safety factor is represented as 10 n s s C01 k e =e s bs a c s s m (2) where c s is called average stress influence factor and is related to cyclic stress, material properties, stress concentration factor and heat treatment method of the material. It can also be obtained in the following equation based on material pulsating cyclic fatigue limit s 0 , c s 2s C01 C0s 0 s 0 (3) wheres C01 iscyclicfatiguestrengthofperfectsymmetry.Itmustbe pointed out that fatigue strength of the bearing can be affected by many factors, such as surface integrity and dimensional accuracies of the bearing cages, material defects and heat treatment conditions, environmental and loading conditions 8. The bearing is supposed to have alonglifetimewhen itsfatigue safetyfactor n s is equal to or larger than the allowable fatigue safety factor n s . It is worth noting that using the endurance limit of the bearing material can theoretically allow designing a bearing of unlimited lifetime. Practically, the bearing lifetime may be limited due to a number of reasons. Examples include that the fatigue strength of the bearing material may not solely be determined by the cyclic Fig. 5. Axial error motion of nested single inner/outer bearing sections subjected to external torque conditions. stresses, other factors, such as the state of stress, bearing machiningandpost-processingconditionsandbearingapplication environment can bring uncertainties to the bearing lifetime. In addition, the endurance limit of the bearing material is normally obtained fromthe SN test, whichis typicallyperformedunderthe uni-axial loading conditions. For the tri-axial loading conditions, the endurance limit on the SN curve should be different. In this consideration, a better way to determining the bearing lifetime is to actually test the bearing under the practical loading conditions. Incontrasttothe designf