立式加工中心机械手的设计
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3 换刀机械手的总体方案设计3.1 设计任务本次设计的主要任务是:自动换刀机械手,实现数控镗铣床的自动换刀,需要换的刀具主要是BT40型刀柄,需要实现的工作是抓刀换刀松刀的动作。主要技术参数:刀具最大重量6kg,双臂回转式换刀,刀臂数量和长度以及直径主要依据配套刀库的设计要求。换刀时间2.5S。3.2机械手的平稳性工业生产要求机械手工作速度快,运动平稳,定位精度高。应注意其影响因素,设计合理结构,以满足要求。3.2.1、影响平稳性以定位精度的因素1、 惯性力的影响图 3.1 惯性曲线机械手速度突变,加(减)速度不连续,会产生巨大的惯性冲击力,以至使工件滑动、部件松动、零件破裂。定位时,大的减速度使臂部往复振动,直接影响定位精度。因此,应根据机械手的运动特性,选择适宜的控制系统,使加(减)速度按所需的运动归路变化,同时,在保证刚度的前提下,减轻机械手运动件的重量。2、结构刚度的影响零件结构刚度性差,配合间隙大及整机固有频率低时,受较小惯性冲击,就发生振动。不但降低定位精度,而且降低机械手寿命。应选择合理结构,提高机械手固有频率及承受惯性载荷的能力。 3、定位方法的影响常用的定位方法中,电气开关的定位精度最低,伺服定位较高,机械挡块的定位最高。4、控制系统的影响电控系统的误差,阀类泄漏,检测元件失灵,挡块偏移等会降低定位失灵。5、驱动源的影响液压、气压、电压及油温波动都会降低平稳性及定位精度,必要时,用蓄能器等稳定液压、气压、电压,用加热器和冷却器控制油温。3.2.2 机械手的运动特性深入分析机械手的运动特点,有利于根据工作条件选择适宜的运动特点。下面为我们所选工业机械手所具有的运动规律,在减速较大时的情形。图 3.2 运动特性曲线按上图的运动,机械手的速度变化呈等加速或不等加速运动,其减速过程亦分为等减速运行和不等减速运行,在呈等加速运行,而不等减速运行时,由于速度行程短,故有利于提高机械手的工作速度。特点:速度变化基本上连续,运动中不会产生冲击,可以满足高速、平稳和定位精度高的要求。3.3机械手运动特性的分类气动机械手:气动机械手的加速或调节系统采用气路节流调速系统,控制系统采用气缸端部节流缓冲装置、气路节流缓冲回路、液压缓冲气等。定位系统采用机械挡块或多点定位几机构定位精度。液压机械手:液压机械手的加速或调节系统油路节流调速系统,控制系统采用油缸端部节流缓冲装置及缓冲回路、减压节流继续能缓冲系统、伺服系统等。定位系统采用关闭电磁换向阀定位精度、机械挡块定位精、伺服系统定位精度度等。电动机械手:电动机械手的加速或调节系统采用电路节流调速系统,控制系统采用反接制动电路、减速电路、凸轮或连杆机构等。定位系统采用电磁制动器、脉冲电路定位精度、机械挡块定位精度等。机械联动机械手:机械联动机械手的加速或调节系统采用凸轮连杆机构,控制系统采凸轮曲线和连杆机构。定位系统采用凸轮基圆及凸轮顶点、连杆极限位置。3.4开关型机械手的速度及位置控制用电气开关、换向阀、节流阀和机械挡块等来控制的机械手称为开关型机械手。液压机械手的速度控制:开关型液压机械手一般采用截流减速方法,少数采用蓄能器或溢流阀减速方法,也可以几种方法一起采用。气动机械手的速度控制:气动机械手有很多优点,但气动的压缩性大,阻尼效果差。符合大的气动机械手采用液压缓冲回路。一般采用的装置是气动-液阻装置。开关型机械手的定位系统:定位系统与速度控制系统有密切的关系,但他们都有其独立性,例如,节流减速后既可以发出指令关闭油路定位,也可以压在挡块上而定位。电气开关定位:电动机械手一般采用电磁制动器定位。当机械手运动到定位点时,行程开关发出信息给电控系统,激励电磁制动器而定位。特点:结构简单,工作可靠,维修方便,但定位精度低。机械挡块定位:一般是在减速后,驱动压力将运动件压在机械挡块上或驱动压力将活塞压靠缸盖而定位,定位精度较高。可分为单点定位或多点定位的挡块机构。3.5机械传动型机械手速度及位置控制为了便于控制机械手的速度及位置,一些专用机械手采用凸轮机构和连杆机构进行驱动。特点:工作速度可以提高而且与主机同步工作而不产生误动作。通过以上论述和比较,选用液压缓冲器和油缸端部缓冲的方式,定位选用机械挡块定位。3.6 机械手类型确定根据以上的介绍,通过比较我确定选用电动机械手。这样选择的原因主要是根据精度和成本的原因。由于是个单独的部件大量生产,成本是非常主要的原因,气动和液压机械手的制造精度要求非常高,成本也就高,而电动机械手作为发展得最为完善的机械手,在精度满足需要的同时,成本是最低的,所以选择了电动机械手。244 总体结构设计4.1 手爪部分设计机械手手爪部分的作用是抓住和放开工件,并且要保证在抓刀后的换刀过程中保证刀具不会重手爪中飞出。目前的加工中心换刀机械手的手爪种类繁多,可以说每个厂家都推出自己的独特的换刀机械手,目前使用最多的有4种机械手,分别是单臂单手式机械手,回转式单臂双手机械手,双手式机械手和多手式机械手。单臂单手式机械手的特点是机械手只做往复直线运动,主要用与刀具主轴和刀库刀座的轴线平行的场合,机械手的插、拔刀运动和传递刀具的运动全都是直线运动,因为没有回转运动所产生的离心力,因为无回转运动所产生的离心力,所以机械手的握刀部分可以比较简单,只需要两个弹簧卡销卡住刀柄即可。但是换刀各动作均需顺序进行,时间不能重合,所以换刀时间较长。例如在转塔头带刀库的换刀系统中,不工作主轴的换刀时间与工作主轴的加工时间重合,可使用这类机械手。回转式单臂双手机械手的两手部成180,手型种类很多,常见的有固定式双手、可伸缩式双手、剪式双手等。这类的机械手可以同时抓住可拔、插位于主轴和刀库(或运输装置)里的刀具,与单臂单手式机械手相比,可以缩短换刀时间。这类机械手应用最广泛,形式也最多。双手式机械手的手臂运动方式有2种,一种是机械手只做往复直线运动的,这样的机械手有双手平行式和双手交叉式,这样的机械手可起运输装置的作用,使用于容量大、距主轴较远的、特别是分置式的刀库和换刀。还有一种是机械手有回转运动的。这2种机械手向刀库还回用过的刀具和选用新刀,均可在主轴正在加工时进行,所以换刀时间较短。多手式机械手的各个机械手顺次使用,可以用语单主轴机床(机械手和刀库为一体),和带双刀库的双主轴转塔头机床。这类机械手的使用者最少。根据以上的分析,手爪部分的结构我选择了回转式单臂双手机械手,而夹刀的部分我选用了钩手的结构,这样选择的原因是钩手具有结构简单,安装拆卸方便,不需要额外的驱动,抓刀方式简单等特点。结构如图4.1所示。图4.1 钩手结构示意图 如图4.1所示,当机械手旋转的时候,钩手与刀柄先接触,由于机械手继续旋转,刀柄对顶柱有挤压作用,顶柱的后面是弹簧,并且定位顶柱没有锁定,所以顶柱收缩到机械手臂内,刀柄顺利进入钩手内,旋转结结束,顶柱通过弹簧的弹力恢复原位,定位顶柱锁顶,顶柱不能移动,卡住刀具,抓刀结束。刀具重量的范围,由于沟手结构的刀爪抓刀后,刀具的重量集中在刀爪内圈的突起上,顶柱受力不到刀具重量的1/10,所以当刀爪抓刀后,由定位顶柱所提供的推力远远大于顶柱所受到的力,所以肯定能把刀具固定住,而不用担心刀具会在机械手旋转的时候掉下来。4.2 机械手手臂的设计机械手工作中运动速度较高,在结构位置应保证运动平稳,这样可以提高机械手运动的平稳性,可以提高机械手适用的可靠性,并提高使用寿命。4.2.1臂部要防止偏重通常臂部处于悬臂的工作状态,在设计臂部、腕部和手部结构时,尽量使其总的重心在支撑中心,防止对支撑中心的偏重。一但偏重,将会产生附加的弯矩,引起导向装置不均匀的磨损。在回转运动中,偏重对回转轴附加有动压力,其方向不断变化,特别是高速及速度突然变化时更加明显,这些都将引起机械手的振动,严重的会造成卡死。预防的措施:1.减轻腕部、手部的重量,并尽量减少偏心载荷。可采用铝合金制造腕部和手部。2.合理分布臂部上各部件重量和增加平衡重,使臂部平衡。3.某些机械手结构上无法避免偏重,则应加强导向支撑,尽量减轻偏重对运动的影响。4.2.2加强臂部刚度提高臂部刚度是减少手部颤动的关键,有利于提高定位精度,故常采用导向形式来加强定位。4.2.3改进缓冲装置和提高配合精度机械手的缓冲装置是保证运动平稳和减少振动的主要措施。机械冲击,它是在臂部运动中与定位装置相碰撞而产生的。它可用缓冲装置来消除。4.2.4采取的措施:1.提高部件的配合精度,减少间隙,有利于运动平稳,特别是高速运动的机械手更需要保证加工精度和提高配合。2.机械手的紧固件在运动中受变载荷的作用必须采用防松措施。综合以上所述,我在设计机械手手臂的时候采用了完全中心对称的机构,并且通过调整螺栓来调整机械手手臂的水平。因为整体的尺寸很小,所以机械手换刀臂的轴的直径比较小,并不适合采用键连接来传动,所以采取了胀缩环这一个标准件来连接机械手换刀臂和机械手换刀臂的轴。胀缩环具有非常好的对中性,并且能够传递非常大的转距,结构简单,非常适用在机构尺寸小的结构中。机械手换刀臂的结构简图如图4.2所示。这个手臂的形状,完全按照中心对称的方式设计,但是为了适应不同型号的刀柄,两边的刀爪是可以拆卸调换的。图4.2机械手换刀臂的结构简图4.3机械手传动结构的设计根据第2章的介绍,我选择凸轮换刀装置作为传动方案。凸轮机械手换刀装置是目前加工中心常用的机构之一,与传统的气动、液压换刀机构相比,它具有换刀速度快、换刀可靠、运动平稳的特点。近年来加工中心得到了广泛的应用。凸轮机械手换刀装置通常由2个凸轮以及相应的机构组成,其中,一个平面凸轮通过连杆机构,用来完成“装刀”与“ 拔刀”动作;另一个弧面凸轮带动凸轮分度机构,用来实现机械手的转位,完成“抓刀”和“换刀”动作。图4.3 凸轮机械手换刀机构原理图1驱动电动机 2减速器 3锥齿轮 4平面凸轮5弧面凸轮 6连杆机构 7机械手 8滚动盘 9电气信号盘凸轮换刀装置的结构原理如图1所示,它主要由驱动电动机1、减速器2、平面凸轮4、弧面凸轮5、连杆6、机械手7等部件构成。换刀时,驱动电动机1连续回转,通过减速器2与凸轮换刀装置连接,提供装置的动力;并通过平面凸轮、弧面凸轮以及相应的机构,将驱动电动机的连续运动转化为机械手的间歇运动。图4.3中,平面凸轮4通过锥齿轮3和减速器2连接,在驱动电动机转动时,通过连杆机构6,带动机械手7在垂直方向作上、下运动,以实现机械手在主轴上的“拔刀”、“装刀”动作。弧面凸轮5和平面凸轮4相连,在驱动电动机回转时,通过滚动盘8(共6个滚珠)带动花键转动,花键轴带动机械手7在水平方向上作旋转动作,以实现从机械手转位,完成“抓刀”和“换刀”动作。电气信号盘9中安装有若干开关,以检测机械手实际运动情况,实现电气互锁。弧面凸轮转角平面凸轮转角 图4.4 平面凸轮和弧面凸轮的运动过程平面凸轮与弧面凸轮的动作配合曲线如图4.4所示。在驱动电动机的带动下,弧面凸轮在7.557.5的范围内,完成机械手80的转位动作。在57.572.5的范围内弧面凸轮、平面凸轮均不产生机械手运动,用于松开刀具。当凸轮继续转动到72.5137.5的范围内,平面凸轮通过连杆机构带动机械手进行向下运动;其中,在72.5117.5范围内,只有平面凸轮带动机械手作向下的运动,机械手同时拔出主轴、刀库中的刀具;在117.5137.5的范围内,因刀具已经脱离主轴的刀座,两凸轮同时动作,即:在机械手继续向下的过程中,已经开始进行180转位,以提高换刀速度。在凸轮转动到117.5242.5的范围内,弧面凸轮带动机械手进行180转位,完成主轴与刀库的刀具交换;当进入222.5242.5的范围时,两凸轮同时动作,平面凸轮已经开始通过连杆机构带动机械手进行向上运动,以提高换刀速度。从222.5起,平面凸轮带动机械手向上运动,机械手同时将主轴、刀库中的刀具装入刀座;这一动作在222.5287.55范围,完成“装刀”动作。接着的287.55302.5范围内,弧面凸轮、平面凸轮均不产生机械手运动,机床进行刀具的“夹紧”动作,这一动作由机床的气动或液压机构完成。在302.5360的范围内,弧面凸轮完成机械手80反向转位动作,在机械手回到原位,换刀结束。3 for the sword overall design of manipulator3.1 design taskThe design of the main task is to: automatically change the manipulator, realize the sword of nc boring and milling machine automatically change the knife, need to change tool is mainly BT40 the style of work, need to achieve is to hold knife knife-in-the action of the sword. LooseThe main technical parameters: tool maximum weight 6 kg, arms rotary change knife, the knife arm number and length and diameter of main basis supporting knife library design requirements. Change the tools time 2.5 S.3.2 the smoothness of manipulatorIndustrial production requirements manipulator speed, smooth movement, high precision positioning. Should pay attention to the impact factors, rational structure design to meet the demand.3.2.1, influence factors of position precision to stability1,Effect of inertia forceFigure 3.1 inertia curveManipulator, add (reduce speed mutations) speed discontinuous, can have a huge impact, to make the work and inertia sliding, components and parts broken loose. Positioning, big reducing speed make brachial ministry reciprocating vibration, directly influence the positioning accuracy. Therefore, should be based on the characteristics of the manipulator movement, selecting the appropriate control system, make add (minus) according to the speed of movement of change, at the same time, in the way that the premise of stiffness, reduce the weight of the manipulator moving parts.2, the influence of the structure stiffnessParts structure stiffness sex differences and, together with the big gap and the inherent frequency low, smaller impact by inertia vibration that happened. Not only reduce the positioning accuracy, and reduce the manipulator life. Should choose reasonable structure, improve the natural frequency of the manipulator and bear inertial load capacity.3 and the influence of the localization methodThe location of the commonly used method, electrical switch positioning accuracy of servo positioning, lowest, high mechanical stop the positioning of the highest.4, the influence of the control systemThe error of the electric control system, the kind of leak, the test components failure, block piece of migration will reduce positioning failure.5, driving sourcesHydraulic, pneumatic, voltage and the oil temperature fluctuations will reduce the stability and precision, when necessary, use the accumulator, hydraulic and pneumatic, voltage stability, with heater and cooler control the oil temperature.3.2.2 manipulator the motion characteristicsIn-depth analysis of the manipulator, which is beneficial to the sport characteristics according to the working conditions of the appropriate choice movement characteristics. Below we chose for industrial robots is the motion law of the slowdown, in the situation. LargerFigure 3.2 movement characteristics curveAccording to the movement, the speed of the manipulator is accelerating or changes such as ranging movement, the deceleration process accelerated also divided into operation and slow down, a slowdown in running range and speed up and running, ranging from running, due to slow down the speed, the short trip to improve the speed of work of the manipulator.Characteristics: speed change, movement of continuous basically wont impact, can satisfy the high speed, stable and positioning precision requirements.3.3 the classification of the manipulator movement characteristicsPneumatic robot manipulator acceleration or adjust the pneumatic system adopt pneumatic throttling speed regulation system, the control system adopts cylinder ends throttling buffer device, pneumatic, hydraulic buffer circuit throttling buffer gas, etc. Positioning system adopts mechanical block piece or more positioning a few institutions positioning accuracy.Hydraulic manipulator of the manipulator: hydraulic acceleration or adjusting system throttle control system, the control system by oil cylinder ends throttling buffer device and buffer circuit, the reduced pressure throttling continue buffer system, servo system, etc. Positioning system adopts closed directional control valve positioning precision electromagnetic, mechanical stop piece of positioning precision, positioning accuracy servo system is spent etc.Electric manipulator: electric manipulator acceleration or regulation system of the circuit throttling speed regulation system, the control system using reverse connect braking circuit, deceleration circuit, CAM or linkage mechanism, etc. Positioning system by electromagnetic brake and pulse circuits positioning accuracy, mechanical block piece of positioning accuracy, etc.Mechanical linkage manipulator: machinery of the manipulator acceleration or adjust the linkage system, adopt CAM link mechanism, and control system adopt CAM curve and the linkage mechanism. Positioning system adopt CAM and CAM, connecting rod and round vertex limit position.3.4 switch type of the manipulator speed and position controlUse electrical switch, reversing valves, throttle valve and mechanical stop to control of the manipulator called switch type manipulator.Hydraulic manipulator speed control: switch type hydraulic manipulator generally USES the closure slowdown, a few accumulator or the way the overflow valve slowdown method, may also several methods used together.Pneumatic manipulator speed control: pneumatic manipulator has a lot of advantages, but pneumatic large compressibility, damping effect is poor. Accord with large pneumatic hydraulic buffer circuit using manipulator.General use of the device is pneumatic-fluid resistance device.The switch of the manipulator type positioning system: positioning system and speed control system has the close relation, but they all have its independence, for example, can not only after a slow throttling instructions close, also can pressure oil positioning in block block and positioning.Electrical switch orientation: general electric manipulator using electromagnetic brakes positioning. When manipulator movement to anchor point, travel switch to send messages of electronic control system, incentive electromagnetic brake and positioning.Features: simple structure, reliable, easy maintenance, low but positioning accuracy.Mechanical stop piece of positioning: general is slowing down, drive after pressure will be moving parts in mechanical stop block pressure or driver pressure will be the piston and cylinder pressure on location, location accuracy is higher. Can be divided into the single point positioning or more positioning of the block piece of institutions.3.5 mechanical transmission speed and the position control of manipulatorIn order to facilitate control the speed of the manipulator, some special manipulator and position of the CAM mechanism and the linkage mechanism driven.Features: the speed of work can improve and and host synchronous work and do not produce false action.Through the discussion above and comparison, choose hydraulic buffer and oil cylinder at the end of the location selection, buffer way mechanical block piece of positioning.3.6 determined manipulator typeAccording to the introduction of the above, through the comparison I select electric manipulator. Such are the main reasons why choose according to the precision and the cause of the cost. Because a single components of mass production, the cost is very main reasons, pneumatic and hydraulic manipulator in manufacturing precision require very high, high cost, and electric manipulator as the most complete development manipulator, precision to meet demand in at the same time, cost is the lowest, and the choice of the electric manipulator.4 overall structure design4.1 PAWS part designThe role of the manipulator PAWS part is to capture and let go of the workpiece, and in ensuring that the change of knife knife after the catch in the process of cutting tool will not guarantee ChongShou claw fly out of.The current processing center for the sword of the manipulator PAWS sort is various, can say that each manufacturer to launch their own unique change the tools at present use most manipulator, there are four manipulator, respectively is a single hand arm of robot arm, rotary hands hands of robot manipulator, and more hands of robot.A single hand arm of robot is characteristic of the manipulator only do reciprocating linear motion, basically use and tool spindle and knife knife a library of parallel axis of the occasion of the manipulator, plug, sports and transfer tool youth movement is all linear motion, because no rotary motion produces the centrifugal force, because there is no rotary motion produces the centrifugal force, so of the manipulator hold a knife parts can be quite simple, just two spring card pin stuck to the handle. But in every action sword all need to order, time cant overlap, so in knife the time is long. For example in turn with the sword of the library tower head change cutters system, not to work with the change of time and sword spindle work the axis of processing time overlap, can use this kind of manipulator.Rotary arm of the manipulator hand into two hands 180 , hand model is a lot of more phyletic, common have fixed the hands, but the telescopic hands, scissor hands, etc. This kind of robot can at the same time holding can pull out, main shaft and knife inserted in library (or transportation device) of knives, and a single hand arm of robot can shorten the sword, compared in time. This kind of manipulator, form is also the most widely used the most.Both hands of robot arm movement there are two ways, one is only do reciprocating linear motion manipulator, such manipulator has hands parallel type of ideas and hands, such manipulator can be up the role of transportation device, used in large capacity, far away from the main shaft, especially in the separation of the library and the change of knife knife. Still another kind is a manipulator of the movement of the rotary has. The two kinds of manipulator to knife library of cutting tools and recycle also choose new knife, all can in the spindle is processing and so in a relatively short time sword.More hands each of robot manipulator, can use language followed single spindle machine (manipulators and knife library as one), and take double the library tower head turned double spindle of machine tools. This kind of manipulator users at least.According to the above analysis, the structure of the PAWS part I chose the rotary arm manipulator, and hands nipped dao part I choose the hook of the hands of the structure, this is the reason for the choice of the hook is simple in structure, convenient installation remove, do not need additional drive, catch a knife way of simple features. Structure is shown in figure 4.1.Figure 4.1 the hook structure schematic drawingAs shown in figure 4.1 shows, when manipulator turns, the hook and the first contact, as a result, the type of handle continues to rotate manipulator blind have extrusion action, the back of the blind is spring, and locating the blind not lock, so blind to the mechanical arm contraction in the handle into the hook, smooth, rotating and, in the end by spring elastic recovery blind in situ, the orientation lock top blind blind, cant move, cutting tools, catch a knife stuck over.The range of tools, because the weight of the structure of the hand knife knife after the claw, cutting tool of the weight of the focus on the sword of the inner ring claw bumps, force of the cutting tools weight not blind 1/10, so when the knife knife after the claw, provided by the positioning of the blind thrust far greater than by blind strength, and so you can put the tool to fix, and not be worried about the tool will be in the fall when rotating manipulator.4.2 the design of manipulator armManipulator movement in the high speed work, the structural position should guarantee the smooth movement, so that it can improve the stability of the movement of the manipulator, can improve the reliability of the manipulator applicable and improve the service life.2 the brachial ministry to prevent lay particular stress onUsually the arm in the working state of the cantilever, in the design department, the wrist and hand arm structure, make its overall focus in support of the support center, prevent the center of lay particular stress on. A but lay particular stress on, will generate additional bending moment, cause orientation device uneven wear. In the rotation movement, attention to move additional pressure to rotate, its direction changes, especially in high speed and speed suddenly change more apparent, which will cause the vibration of the manipulator, serious can cause jammed.Prevention measures:1. Reduce the wrist, hand weight and reduce eccentric load. Can use aluminum alloy manufacture of wrist and hand.2. The reasonable distribution of each component of weight on the arm and increase the balance weight, make brachial ministry balance.3. Some structure cant avoid manipulator of lay particular stress on, should be strengthened, and try to reduce guide support to the influence of lay particular stress on sports.4.2.2 strengthen brachial ministry stiffnessImprove the brachial ministry is to reduce the hand trembling stiffness key, help to improve the precision, reason often used to strengthen the guidance form positioning.4.2.3 improvement and improve the buffering devices with precisionThe buffering devices is to guarantee the manipulator smooth movement and reduce vibration of the main measures.Mechanical impact, it is in the movement of the arm and positioning device collide and of generation. It is used to eliminate the buffering devices.4.2.4 take measures:1. Raise the parts with precision, reduce gap, be helpful for the smooth movement, especially the movement of the manipulator needed to ensure that more machining accuracy and improve coordination.2. Of the manipulator in sports change by fastener load role against pine measures must be adopted.Comprehensive above mentioned, I in the design of the manipulator arm when completely symmetrical institutions, and center by adjusting bolt to adjust the manipulator arm level. Because the overall size is small, so the manipulator arm of the shaft of the sword in relatively small diameter and is not suitable for the key link to drive, so take the bilge shrink rin
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