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自动换刀机械手装置设计,自动,机械手,装置,设计
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A Novel Dual-Cam Linkage Drive Automatic ToolChanger Abstract In this paper, a novel automatic tool changer for horizontal machin-g center is presented. The mechanism and working principle of the automatic tool changer are introduced. Push-pull rod and tool changer run synchronously driven by dual-cam linkage. The key structure, dual-cam linkage, is analyzedand designed in details. Cam curves of two sets of cams, one of which drivespush-pull rod and another drives tool changer, are selected by way of compre-hensive evaluation.The transmission unit is designed. An application example of this novel automatic tool changer in MDH65 Horizontal Machining Center ispresented and motion simulation is carried out.The result shows that the noveldual-cam linkage automatic tool changer works more efficiently and reliablythan general with rational matching design of two sets of cams. Keywords: ATC. Dual-cam linkage. Cam curve. Comprehensive evaluation. Motion simulation. 1.Introduction Automatic Tool Changer (ATC) is a system that automatically performs tool ex-change between the spindle and the tool magazine of a machining centre. It plays an important role in reducing the machine idle time, which can improve work efficiency and reliability significantly. Various types of ATC with quite different working principles have been applied in machining centers. Yan and Chen studied the configuration synthesis of machining centers with tool change mechanisms and the classification of automatic tool changers in 1 and 2. Reference 3 investigated types and design characteristics of automatic tool change mechanism. According to the difference of drive mechanism for tool changer, it mainly includes two types of ATC, one of which is hydraulic drive ATC, another is mechanical cam drive ATC. Reference 4 compared those two type of ATC and indicated that the latter has more advantage because of higher efficiency and reliability. A tool changer driven by double-follower cam gear, which can be used in both vertical and horizontal machining center, was researched on in 5 Based on the investigation of existing types of ATC and research on ATC working process6, a novel type of ATC driven by dual-cam linkage is considered for hori-zontal machining center. 2 The Dual-Cam Linkage Drive ATCGenerally, there are two parts participating in tool exchange in a machining center with ATC. A push-pull rod in spindle is used to push or pull the tool holder, so that the tool in the front-end of spindle would be clamped or unclamped, and a tool changer is used to exchange tools between the spindle and tool magazine. Tool changer and push-pull rod should work sequentially, otherwise serious problems, for example, damage to tools, spindle and magazine, may occur. 2.1 Mechanism of Dual-Cam Linkage Drive ATC A typical cam drive ATC used popularly is shown in Fig. 1. The two parts participat-ing in tool exchange are driven separately. In tool push-pull part, the push-pull rod is driven by hydraulic pressure, and the tool in the front-end of spindle will be clamped or unclamped according to the movement of push-pull rod. In the tool exchange part, the power is from a motor, and the tool changer is controlled by cams. In order to ensure the two parts work sequentially, several limit and proximityswitches are used to coordinate the positions of push-pull rod and tool changer. In this way, the process of tool exchange is complex, so it costs much time and the reliability is difficult to ensure. The novel type of dual-cam linkage drive ATC could resolve above problems. The schematic diagram of dual-cam linkage ATC mechanism is shown in Fig. 2. As shown in Fig. 2, Tool push-pull part and toll exchange part are driven by one motor. One power line is motor, cam, push-pull rod, disk spring and tool, and the other power line is motor, coupling, transmission unit, cam, tool changer and tool. These two parts would work synchronously driven by one motor. This structure can simplify tool exchange process and save time remarkably, and rational design of dual-cam linkage can ensure that the working timing of two parts match with each other perfectly, so tool exchange would be more accurately and reliability. Fig. 2. The schematic diagram of dual-cam linkage drive ATC2.2 The Working Principle of Dual-Cam Linkage Drive ATC The main innovation of dual-cam linkage drive ATC is the application of a new mechanism, in which tool push-pull part and tool exchange part are driven by one motor synchronously. The working principle is shown in Fig. 3. Push-pull rod in the spindle is controlled by cam and disk spring, to clamp or un-clamp the tool which is fixed in the front-end of spindle. Camis composed of two cams, a slot cam inlaid on one side of a globoid cam. The slot cam controls the trans-lation movement of tool changer, which can draw tool out from or insert tool into spindle. The globoid cam controls the rotation movement of tool changer, which can exchange tools between tool magazine and spindle. When machining center gives tool exchange signal, motor starts, then push-pull rod and tool exchange manipulator will work in timing separately controlled by cam and cam , which are driven by the same motor. Therefore, the process and control are simple, which make it possible to realize reliable operation and save tool exchange time. 3 Design of Dual-Cam LinkageIn design, dual-cam linkage is the most challenging part. The movement of cam and cam must match with each other perfectly to insure high reliability, and the power transmission unit between motor and cam the structure of machining center. should be designed reasonably based on structure of machining center.3.1 The Matching Design for Cam Timing Chart According to the functional requirements of cams in dual-cam linkage drive ATC, the types of cams are selected, shown in Table 1. Supposed the transmission ratio of two sets of cams is 1:1. In other words, two sets of cams can be regarded as located on a same axis. In order to realize coordinated motion of push-pull rod and tool changer, the cam timing chart are designed as Fig. 4 based on the working principle of dual-cam linkage drive ATC. c is angular displacement of the cams. f is linear or angular displacement of the cam followers. It is mm for translating follower of plate cam, and it is deg for oscillat-ing follower of slot cam and indexing follower of globoid cam. 1. Indexing follower rotates 90anticlockwise and drives tool changer to grasp tools while globoid cam rotates from c =7to c=62. 2. Plate cam pushes push-pull rod to unclamp the tool in the front-end of spindle while it rotates from c =60to c =85 3. Oscillating follower drives the tool changer to draw out tools from spindle and tool magazine while slot cam rotates from c=85to c =152. 4. Indexing follower rotates 180clockwise and drives tool changer to exchange tools between spindle and tool magazine while globoid cam rotates from =122to c =242. 5. Oscillating follower drives the tool changer to insert tools into spindle and tool magazine while slot cam rotates from c =212to c =282. Then, the slot cam invo-lutes 6. Disk spring pushes push-pull rod back to clamp the tool assembled into spindle, and plate cam rotates fromc =280to c=300, then involutes. 7. Indexing follower rotates 90clockwise and drives tool changer to return to for-mer condition while globoid cam rotates from c =302to c =352. Then, the globoid cam involutes. 3.2 The Analysis and Optimum Design of Cam Curve Cam curve is closely related to the kinematics characters, dynamic performance, effi-ciency and service life of cam mechanism. Its important to select optimum cam curve for different working periods. The main features of cam curve are as follows: Dimensionless maximum velocity Vm: It is related to maximum momentum, ac-cording to P=mv, where P is momentum, is mass, and v is velocity. Vmhas influ-ence on pressure angle and size of cam. If m is large, its necessary to choose the cam curve, of which is small. Dimensionless maximum acceleration Am: It is related to maximum inertial force, according to f=ma, where fm is inertial force, m is mass, and a is acceleration. The extrusion force between cam and follower increases with increase of Am , and the am-plitude of vibration force increases too. If velocity curve is discontinuous. Amwould be infinite, and impact vibration will occur. It is reliable to choose a cam curve, of which Am is small, in high-speed cam. Dimensionless maximum jerk Jm: It is the differential of acceleration with respect to time. Jm is mainly related to the vibration of follower. If acceleration jumps on one point, Jm is large in this point and strenuous vibration appears. To reduce vibration, it is better to choose a cam curve, of which Jmis small. In cam curve design of dual-cam linkage, the mainly requirements are: 1. All cams should run sequentially and smoothly. 2. The plate cam and slot cam have no-impact and less vibration in operation to avoid destructing tools. 3. The indexing precision and accurate positioning of globoid cam should be improved to ensure tool exchange accuracy 4. Considered the service life of globoid cam, thin ridge must be avoided. To avoid rigid impact caused by velocity jump and flexible impact caused by ac-celeration jump is the basic principle in selecting cam curve. It is required that the features Vm, Amand Jmare as small as possible, but there is no cam curve, of which the features can be all small. So an optimum design method of cam curve, comprehensive evaluation of cam curve, is presented. Comprehensive evaluation is based on fuzzy theory and maximum degree of mem-bership principle7. All factors related to the project would be concerned, and the solution comes from comprehensive evaluation of them. The process of cam curves optimum design in dual-cam linkage is as follows: 1. According to cam curve design standard and practical design experience, candi-date set of cam curve is founded, which includes polynomial curve, modified trape-zoid curve (MT), modified sine curve (MS), and modified constant velocity curve (MCV)8. 2. Consider the features of cam curve Vm, Amand Jm as evaluation factors. They are specified in Table 2. 3. Through comparing the mainly requirements of cam in dual-cam linkage and the effect aspect of every cam feature, and analyzing the evaluation factors, fuzzy subsets are established. Practical design experience is also invited. 4. Present membership satisfied grade of each cam curve in candidate set. 5. Based on set theory, select optimum cam curve for each cam in dual-cam link-age. The result is shown in Fig. 5. Fig. 5. The result of optimum design for cam curve Compared with Fig. 4 and Fig. 5, it shows that modified sine curve (MS) is selected for plate cam and slot cam, and modified constant velocity curve (MCV) and modified sine curve (MS) are selected for globoid cam in their different working periods. 3.3 The Design of Transmission Unit In dual-cam linkage drive ATC, two sets of cams are driven by one motor, so the transmission unit between them must be designed on the basis of the concrete struc-ture of machining center. In a general way, as shown in Fig. 2, the motor is fixed near the rear end of spindle, and the power from motor pass through speed reducer to drive cam axis directly. Then, the transmission unit should transfer power from cam axis to camaxis. Because of the indexing operation of globoid cam, the torque of camaxis appears positive-negative changes in one cycle, which tends to induce fluctuation. It is necessary to ensure the cam axis runs smoothly, so that it is possible to give full scope to the indexing precision of globoid cam, and the slot cam gets stable operation to avoid breakage when drawing tool out from or assembling tool into spindle. So neither the chain transmission with pulsation nor gear transmission with interval is suitable. The solution is to choose synchronous belt, which is with constant velocity and non-slip, as the transmission unit. The arrangement of synchronous belt transmission is dependent on the concrete structure of machining center. If the size of machining center is large, it is permissible to design multiple level synchronous belt transmission as shown in Fig. 2.4 The Application Example Dual-cam linkage drive ATC has been applied in MDH65 Horizontal Machining Center. The ATC structure is similar to the one shown in Fig. 2. The cams are designed according to the above analysis, and the design result is shown in Fig. 6. Transmission unit is constituted by two level synchronous belt. The motor is fixed near the rear end of spindle. Based on the limitation of the structure of MDH65, a set of cam-linkage mechanism including a couple of bevel gears is proposed to drive tool changer. Based on the virtual prototype technology, a motion simulation of the ATC is car-ried out. Supposed a tool exchange cycle time is 2 seconds, we get motion curves of two sets of cams from motion simulation. The displacement curve diagram of cams is shown in Fig. 7. The displacement curves are continuous and smooth, without jump, and match with Fig. 5. As shown in Fig. 8, the velocity curves of cams are all continuous. Slot cam and globoid cam velocity curves are smooth. There are two cusps in plate cam velocity curve, but one happens in middle time of plate cam pushing push-pull rod and the other happens in middle time of disk spring pushing push-pull rod back, so they wouldnt cause impact when tool holder unclamps or clamps the tool. From velocity curves, no rigid impact would occur to cause damage. As shown in Fig. 9, it is acceleration curve diagram of cams. We can see there are several cusps in plate cam and globoid cam acceleration curves. They would cause flexible impact and cant be avoided easily, but that is acceptable in a certain range. Fig. 7. Displacement curve Fig. 8. Velocity curve Fig. 9. Acceleration curveThe result of motion simulation shows that every part of the ATC has noninterference;two sets of cams work in coordination; tool exchange process is accurate and reliable. In practical test, the number of normal tool exchange operation times has reached 20000 and the minimal tool to tool change time (T-T) is 2 seconds.5 ConclusionIn this paper, a novel dual-cam linkage drive ATC is derived based on the typical cam drive ATC. The mechanism and working principle are described. Analysis and design of key structure, dual-cam linkage, are introduced in details. The method comprehen-sive evaluation is invited in cam curve design. An application example is presented for demonstrating this new type of ATC, and motion simulation is carried out. The result shows that dual-cam linkage drive ATC works normally applied in horizontal machining center. It simplifies tool exchange process remarkably through dual-cam linkage. Tool exchange efficiency and reliability are improved. Along with the devel-opment of machine tool industry, this new type of ATC has a wide application prospect. AcknowledgmentsThis work is supported by National Natural Science Foundation of China by Grant No.50675027, and Dalian Municipal Science and Technology Commission by Grant No.2006A12GX003. The authors are grateful to the industrial partner, Dalian Ma-chine Tool Group Corp., who produced MDH65 Horizontal Machining Center, and made dual-cam linkage drive ATC used in this study. And thank all people made contribution in this study. 摘要在本文中，说的是荷兰中心的一种新型卧式机自动换刀装置，介绍了换刀装置的自动控制的机理与工作原理，推拉棒和换刀连着双凸轮连杆机构同步运行。关键结构、双凸轮连机构进行了分析和设计细节。两组凸轮凸轮曲线,其中一个驱动器推拉棒和另一个驱动器进行换刀,选择通过按压-然后综合评估传输单元设计以及设计传动装置。这里的一个应用实例这种新颖的自动换刀工具改变MDH65卧式加工中心提出并进行运动仿真。结果表明,这个新型的双凸轮连杆自动换刀工具更有效、可靠地工作，比一般的双凸轮设计更加合理匹配。关键词：ATC双凸轮连杆机构、凸轮曲线、综合评价、运动仿真 1.背景介绍 自动换刀装置（ATC）是一个系统自动执行工具 它主要是执行加工中心的主轴与刀具之间的换刀。它扮演一个非常重要的作用，减少了机器的空闲时间，从而显著的提高了工作效率和可靠性。各种类型的ATC有截然不同的工作原理被应用加工中心,燕和陈研究了配置的综合加工中心与工具变化机制和自动的分类工具更换在1和2。参考3调查类型和自动的设计特点工具改变机制。根据不同的驱动机制的工具变换器,它主要包括两种类型的ATC,其中一个是液压传动ATC,另一个是机械凸轮传动ATC。这两个类型的参考4相比ATC和表示,后者由于更高的效率和更有优势可靠性。工具改变由double-follower凸轮装置,可用于水平和垂直方向的加工中心,研究在5基于现有类型的ATC的调查和研究空中交通管制工作过程,一种新的ATC双凸轮连杆驱动型是水平加工中心。2. 双凸轮联动ATC 一般来说，有两个部分参与工具交换在加工中心与ATC。在主轴上的推拉杆用于推或拉的工具夹具，从而使在主轴的前端的工具将夹紧VS松开，和一个工具换用于主轴和刀具库之间交换的工具。工具换和推拉杆应依次工作，否则严重的问题，对例如，工具，主轴和杂志的损坏，可能会发生。2.1双凸轮联动ATC机制 一个典型的凸轮驱动系统普遍采用如图1所示。这两部分都在换刀分别驱动。在工具推拉，推杆由液压驱动E，在主轴前端工具将夹紧或松开按推拉杆的运动。在刀具交换的一部分，功率从电机和换刀控制通过凸轮。为了保证这两个部件的工作顺序，有几个限制和接近开关被用来协调的位置的推拉棒和换刀装置。以这种方式，过程工具的交换是复杂的，因此它花费了很长时间，而且可靠性很难保证。 双凸轮驱动联动ATC的新型可解决上述问题。该的双凸轮联动ATC机构示意图2，工具推拉部分及收费交换部分由一个驱动马达。一电源线是电机，凸轮，推拉杆，碟形弹簧和工具，以及其它的电力线是马达，联轴器，发送部，凸轮，换刀和刀具。这两部分会由一个电机工作时同步驱动。这种结构可以简化工具交换过程，节省时间显着，而双设计合理凸轮连杆可确保两个部分的工作定时相互匹配完美，所以工具交换会更准确和可靠性。图2.双凸轮驱动联动ATC的示意图图3.双凸轮连杆驱动ATC的工作原理2.2双凸轮连杆机构驱动ATC的工作原理 双凸轮驱动联动ATC的主要创新点是一个新的应用机构，其中，工具的推挽部分和刀具交换部由一个驱动电机同步。工作原理示于图 3。在主轴推挽杆由凸轮控制和碟形弹簧，夹紧或未夹紧被固定在主轴前端的工具。凸轮由两凸轮，在弧面凸轮的一侧上的槽凸轮镶嵌。槽凸轮控制反换刀的特征研的运动，它可以借鉴的工具，或插入到工具主轴。该弧面凸轮控制换刀的旋转运动，从而可以刀库和主轴之间的交流工具。当加工中心提供的工具交流信号，电机启动，然后推拉杆和换刀机械手将在定时工作通过凸轮和凸轮，其通过所述驱动单独控制相同的电机。因此，处理和控制是简单的，这使得有可能实现可靠运行，节省换刀时间。3. 双凸轮连杆机构的设计 在设计中，双凸轮连杆机构是最具挑战性的部分。凸轮与凸轮的运动必须完全匹配，以确保高可靠性，电机与电机之间的功率传输单元根据加工中心的结构合理设计凸轮。3.1凸轮配时图的匹配设计 根据在双凸轮连杆凸轮的功能需求驱动的ATC，该类型凸轮被选择，如表1所示. 假定两组凸轮的变速比为1：1。换句话说，两套凸轮可为位于同一轴线被视为。为了实现协调推拉杆和换刀的运动，凸轮定时图被设计成图。 4基于双凸轮连杆驱动ATC的工作原理。是凸轮的角位移。 是线性或角位移 C F凸轮从动件。这是毫米平移板凸轮的追随者，它是为度摆动槽凸轮与弧面凸轮分度跟随的追随者。 在一个工具交换周期中，过程如下：1. 分度从动件转动90逆时针转动，带动刀具掌握工具而弧面凸轮旋转C = 7到C = 62。2. 盘形凸轮推动推拉杆松开刀具在主轴前端在旋转的C = 60从到C = 853. 摆动从动件驱动换刀抽出工具主轴和刀库而槽凸轮转动时从C = 85到C = 152。4. 分度从动件转动180顺时针带动主轴、刀库换刀之间的交流工具，而弧面凸轮转动C = 122从到C = 242。5. 摆动从动件驱动刀具插入主轴、刀库工具槽凸轮转动时从C = 212到C = 282。然后，槽凸轮的作用琵琶6. 碟形弹簧推推拉杆背夹工具组合为主轴，与盘形凸轮旋转C = 280从到C = 300渐开线。7. 分度从动件转动90顺时针带动刀具回到旧日的条件而弧面凸轮转动C = 302从到C = 352。然后，弧面凸轮渐开线。 3.2凸轮曲线的分析与优化设计凸轮曲线是密切相关的凸轮机构运动学特征，动力性能，效率和使用寿命。选择最佳的凸轮曲线是非常重要的对于不同的工作周期。是凸轮曲线的主要特点如下：量纲最大速度V：它与最大动量，AC-米盘带于P = MV，其中P是动量，m为质量，v是速度。 V有十字形米ENCE压力角和凸轮的大小。如果m为大，这是必要选择凸轮曲线，其中V是小的。米因次最大加速度答：这涉及到最大的惯性力，米根据F =马，其中f是惯性力，m是质量，a是加速度。该凸轮和从动之间挤压力与A的增加，以及上午增加的振动力也增加幅度。如果速度曲线是不连续的，一个想米是无限的，并且不会发生冲击振动。它是可靠的选择凸轮曲线的其中A是小的，在高速凸轮。因次最大挺
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