Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21F—WORKING OR PROCESSING OF METAL WIRE
  • B21F11/00—Cutting wire
  • B21F11/005—Cutting wire springs
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21F—WORKING OR PROCESSING OF METAL WIRE
  • B21F3/00—Coiling wire into particular forms
  • B21F3/02—Coiling wire into particular forms helically

Definitions

• the invention relates to a method for producing coil springs by spring winds by means of a numerically controlled spring coiling machine according to the preamble of claim 1 and to a suitable for performing the method spring coiling machine according to the preamble of claim. 7
• Coil springs are machine elements that are required in numerous applications in large numbers and different designs. Coil springs, which are also referred to as twisted torsion springs, are usually made of spring wire and designed depending on the load in use as tension springs or compression springs. Compression springs, in particular suspension springs, are needed for example in large quantities in the automotive industry.
• the spring diameter is constant for cylindrical coil springs over the length of the springs, but it may also vary over the length, e.g. with conical or barrel-shaped coil springs. Also the total length of the (unloaded) spring can vary widely for different applications.
• Coil springs are nowadays commonly manufactured by spring winches using numerically controlled spring coiling machines.
• a wire (spring wire) is fed under the control of an NC control program by means of a feeding device of a Umformeinrich- device of the spring coiling machine and formed by means of tools of the forming device to a coil spring.
• the tools usually include one or more wind pins that can be adjusted with respect to their position for the determination and possibly for changing tion of the diameter of spring coils and one or more pitch tools, through which the local pitch of the spring coils is determined at each stage of the manufacturing process.
• a finished coil spring is cut off from the supplied wire under the control of the NC control program by a cutter.
• Spring wind machines are generally intended to produce many springs with a specific spring geometry (nominal geometry) within very narrow tolerances at high unit output.
• functionally important geometry parameters u.a. the total length of the finished coil spring in the unloaded state. Through the total length u.a. the installation dimensions of the spring and the spring force determined. If particularly high unit performance is to be achieved, a spring coiling machine can be designed so that the wire is fed continuously without interruption and a cutting device with a rotating cut is used. Then the wire feed must not be interrupted even for the cut.
• DE 103 45 445 B4 shows a spring coiling machine which has an integrated measuring system with a video camera, which is directed at that area of the spring coiling machine in which the shaping of the spring begins.
• An image processing system connected to the video camera with corresponding evaluation algorithms should allow checking the diameter, the length and the pitch of the spring during production and it should be possible to change these spring geometry parameters by feedback to the motor-adjustable processing tools during production , After completion, the finished spring is separated from the wire with a vertical cut.
• the applicant's DE 10 2010 014 385 A1 describes a controlled spring winding method and a spring coil machine suitable for this purpose.
• a desired desired geometry of the helical spring and an NC control program suitable for generating the desired geometry are defined.
• the actual position of a selected structural element of the helical spring is measured relative to a preferably machine-fixed reference element in a measuring range which has a finite distance from the shaping device in the longitudinal direction of the helical spring. The distance is smaller than the total length of the finished coil spring.
• the measured actual position is compared with a target position of the structural element for the measurement time to determine a current position difference representing the difference of the actual position to the target position at the measurement time.
• a pitch tool of the forming device is controlled in dependence on the position difference. After completion of the spring this is separated with a vertical cut from the wire.
• the process can include series made by long coil springs with very little dispersion of the overall length.
• Regulated automated spring wind methods require exact measurement results in order to achieve the desired quality of the finished springs.
• the wire is fed continuously to the former and a measurement on the coil spring is made while the feed is in progress.
• the wire feed is thus not interrupted for the measurement, so that the wire moves during the measurement.
• the finished coil spring is separated by a rotating flying cut from the supplied wire.
• rotating flying cut here means that the cutting tool when cutting a rotating movement and that the wire moves during the cut, or that the wire feed for the cut is not interrupted. With this type of cut it is therefore not necessary to interrupt the wire feed for the cut.
• a measuring device for performing a measurement on the coil spring is provided and it is further provided that the cutting device has a rotating drivable cutting tool, the finished coil spring at the end of the forming operation can separate a rotating flying cut to the supplied wire.
• the wire is fed at a constant feed rate. It is also possible that the feed rate varies continuously between larger and smaller values, but without being reduced to zero.
• a desired nominal geometry of the helical springs to be produced and a corresponding NC control program suitable for generating this desired geometry are defined.
• the coordinated working movements are then repeated cyclically.
• control devices in embodiments of spring wind machines according to the invention have a programmable logic controller (PLC) which can be programmed digitally. To generate recurring coordinated work movements, this control is cycle-oriented.
• PLC programmable logic controller
• a programmable controller has inputs, outputs and an operating system, also referred to as firmware.
• Input cards are connected to the inputs via which, for example, sensor signals are read in via the state of the machine.
• Actuators at the outputs of the controller control the machine.
• the user program can be loaded via an interface.
• the user program cyclically determines the switching of the outputs depending on the inputs after a certain clock cycle.
• the operating system informs the user program cyclically about the current positions of encoders, eg sensors. In this way, the user program switches the outputs in such a way that the programmed function sequence results.
• the cycle time of typical deratiger controls is today in the range of one hundredth of a second, ie in the range of several milliseconds. According to the observations of the inventors, it is generally not sufficient to synchronize trigger signals for measurements with this clock of the controller.
• the measurement time is synchronized with the NC-controlled movements of devices of the spring coiling machine with a temporal accuracy that is greater than a cycle time of the control of the spring coiling machine.
• the timing accuracy of the determination of the measurement time is less than 10 ps.
• the accuracy can be in the range of 1 ps.
• the temporal accuracy of the determination of the measurement time may be at least one order of magnitude, preferably at least two orders of magnitude more accurate than the cycle time.
• a 1 psian range is more than three orders of magnitude (more than a factor of 1000) more accurate than a several millisecond cycle time of the underlying controller.
• this time-precise control of the measuring device is achieved in that the measuring time based on cycle boundaries or by the timing of the control by a time stamp method over a (individually set or determinable for each measurement time) time interval between a cycle limit of the controller and the Measuring time is specified.
• the controller may include an instruction that, after the beginning of a certain cycle of the underlying control, there is still a certain time interval, which is shorter than the cycle time. hen before the trigger signal or the trigger for the measuring device is generated.
• the timing precision of the definition of the measurement time is independent of the cycle times of the underlying controller.
• This procedure is particularly advantageous in the temporal coordination of a measurement with the separation of a finished spring from the supplied wire. If, for example, the total length of the finished spring is to be measured, there is a risk, if the measurement is too early, that the spring is not completely finished at the time of measurement and, accordingly, the finished spring has a significantly greater overall length than the measurement result indicates. On the other hand, if the measuring time is too late, for example at a point in time at which the cut has already begun, then a displacement of the spring that has just been separated may already have taken place, so that a measurement can no longer be carried out with the required accuracy.
• a trigger signal is generated for the measuring device at a measuring instant which is immediately before engagement of the cutting tool in the wire.
• the geometrical distance between the wire and the cutting tool moving toward the wire may, for example, be in the range of one to three times the wire diameter.
• the time interval between the measurement time and the first contact contact between the wire and the cutting tool should preferably be in the range of a few microseconds, for example 10 ps or less. The time interval should be as constant as possible for each cutting process in order to obtain reproducible spring geometries.
• the measurement is preferably carried out without contact, in particular with optical measuring means.
• a load sermesssystem be used.
• a camera with a two-dimensional image field is used for the measurement, and the measurement area is placed in the image field of the camera.
• Camera-based measurement systems with powerful image processing hardware and software are commercially available and can be used for this purpose.
• program time function refers to a function that refers to specific locations within the NC control program.
• the achievement of a specific NC block corresponds to a specific program time or a point in time within the program sequence Sequence of program steps during program execution If, for example, a trigger signal (trigger) is required to control an image acquisition by a camera during a specific phase of the program execution, this triggering sesignal be triggered by a program line present at the appropriate place. This signal is then output by the PLC. This can lead to measurement errors. The present application teaches how such measurement errors can be avoided or reduced to a tolerable level.
• Trigger signals are directly linked in the program with certain positions of the machine axes, eg with the machine axis of the wire feed and / or with the machine axis for the position of the pitch tool.
• a time in a program time function thus corresponds to a location in the movement curve of one or more machine axes.
• the program time function results in times (program times) within an NC program that are synchronous with the progress of the spring production.
• the program time function is also a path function with respect to the movements of machine axes.
• a program time function also corresponds to a path function of the wire feed.
• the invention also relates to a numerically controlled spring winding machine, which is particularly configured for performing the method. It has a feed device for feeding wire to a forming device and a forming device with at least one wind tool, which essentially determines the diameter of the coil spring at a predeterminable position, and at least one pitch tool whose engagement on the developing coil spring, the local slope of Coil spring determined. Further, a cutting device for cutting a finished coil spring from the supplied wire after completion of a forming operation, a measuring device for making a measurement on the coil spring during the forming operation, and a controller for controlling the feeder, the forming device, the measuring device and the cutting device based on a NC control program provided.
• the feeder is configured for a continuous supply of the wire, so that the wire of the forming device is continuously, that is supplied without interruption for the measurement and a measurement can be performed on the coil spring while the feed is running. Also for the cut no interruption of Zufuhhik is necessary.
• the cutting device has a rotating drivable cutting tool and the spring coiling machine is configured such that the finished coil spring can be separated by a rotiende flying cut from the supplied wire.
• the control device is preferably configured in such a way that a trigger signal for the measuring device is generated at a measuring instant which is immediately before engagement of the cutting tool in the wire. This allows exact measurement results, in particular with regard to the measured spring length.
• the measuring time is preferably predetermined with a time accuracy which is substantially greater than the accuracy that would be possible if the measuring times were exclusively linked to the cycle time.
• the temporal accuracy of the determination of the measurement time point may be less than 10 ⁇ and / or at least one order of magnitude more accurate than the cycle time.
• FIG. 1 shows a schematic overview of an embodiment of a spring coiling machine with parts of the feeder and the forming device
• Fig. 2 shows a perspective view of mounting assemblies for in
• Fig. 1 shown spring coiling machine
• Fig. 3 shows a phase in which a finished spring is separated from the wire by means of a rotating cut
• Fig. 4 shows schematically the basic principle of the operating mode: continuous wire feed with rotating flying cut;
• Fig. 6 shows at the top a speed-time diagram of the feeding speed of the wire feed and below an associated speed-time diagram of the moving speed of the cutting tool and the timing of a measuring time point.
• FIG. 1 shows some structural elements of a CNC spring coiling machine 100 according to an embodiment of the invention.
• FIG. 2 shows details of mounting assemblies not shown in FIG. This includes an optional Feder Operationsseinrich- device 210 with an upwardly open angle plate 221, which can support longer springs.
• the spring coiling machine 100 has a feeder 1 10 equipped with feed rollers 1 12, which can supply successive wire sections of a wire feed and guided by a straightening unit wire 1 15 with numerically controlled feed speed profile in the region of a forming device 120.
• the wire is guided on the outlet side through a wire guide 1 16.
• the feeder can also be referred to as a feeder, according to the wire feed can also be referred to as wire feed and the feed rate as the feed speed.
• the wire is converted into a helical spring by means of numerically controlled tools of the forming device.
• the tools include two offset by 90 ° angularly wind pins 122, 124 which are aligned in the radial direction to the central axis 1 18 and the position of the desired spring axis and are intended to determine the diameter of the coil spring.
• the position of the wind pins can be changed to the default setting for the spring diameter when setting along the lines shown in phantom and in the horizontal direction (parallel to the feed direction of the feeder 1 10) to set up the machine for different spring diameters. These movements can also be carried out with the aid of suitable electric drives under the control of the numerical control.
• a pitch tool 130 has a tip oriented substantially perpendicular to the spring axis which engages the turns of the developing spring.
• the pitch tool can be moved parallel to the axis 118 of the developing spring (ie perpendicular to the plane of the drawing) by means of a numerically controlled adjusting drive of the corresponding machine axis.
• the wire fed during spring production is moved by the pitch tool according to the position of the pitch tool in the direction parallel to the spring axis pushed by the position of the pitch tool, the local slope of the spring is determined in the appropriate section. Gradient changes are effected by axis-parallel process of the pitch tool during spring production.
• the forming device has another, vertically downwardly deliverable incline tool 140 with a wedge-shaped tool tip, which is introduced when using this pitch tool between adjacent turns.
• the adjustment movements of this pitch tool are perpendicular to the axis 1 18. This pitch tool is not engaged in the manufacturing process shown.
• a numerically controllable cutting device 150 is mounted with a cutting tool 152 which, after completion of a forming operation, separates the manufactured coil spring from the supplied wire supply with a rotating working movement.
• the counterpart element for the cutting tool is a mandrel 155 (cutting mandrel), which is located inside the developing spring and has an oblique cutting edge 156, which cooperates with the cutting tool during separation.
• the spring coiling machine operates with a continuous wire feed or wire feed in conjunction with a flying rotating cut.
• the cutting device is for this purpose, driven by a rotary machine axis, placed in a rotating working movement, which runs in a plane perpendicular to the spring axis 1 18 and is characterized in Figs. 1 and 3 by rotating arrows.
• the circulation can be circular or elliptical, for example.
• the direction of rotation (clockwise or counterclockwise) depends on the direction of the wind. It can be wound both right and left. In the example case
• the cutting tool rotates clockwise.
• the rotational speed is usually non-uniform.
• the cutting tool 152 cuts through the wire 15 as it approaches the lower turning point of the revolving working movement.
• the upper side of the dome 155 of the cutting device serves as a counter element for the moving cutting tool and provides an oblique cutting edge which, together with the correspondingly shaped cutting contour of the cutting tool, enables a clean cut through the continuously shaped wire.
• the basic principle of this operating mode is again shown schematically in FIG. 4 with the same reference numerals.
• the wire 1 15 is continuously fed or fed or fed with a constant or varying finite feed rate V z . There is thus no stopping of the supply of wire via the production of many successive springs. This increases the piece performance. If the wire feed or the supply device is running constantly, the wire supply 157, which is held on a reel, for example, need not be constantly accelerated and decelerated. This also applies to the drives of the feeder and the tools. As a result, the energy requirement per spring is reduced in comparison to methods with a standing cut, in which the wire feed for the cutting process must be stopped.
• the spring coiling machine is set up to measure spring data such as the diameter and / or length of a spring after production and the finished springs depending on the result of the measurement automatically sorted into good parts (spring geometry within the tolerances) and bad parts (spring geometry outside the tolerances) and, if necessary, into further categories.
• spring data such as the diameter and / or length of a spring after production and the finished springs depending on the result of the measurement automatically sorted into good parts (spring geometry within the tolerances) and bad parts (spring geometry outside the tolerances) and, if necessary, into further categories.
• the spring is measured directly after the spring winch shortly before cutting.
• the machine is stopped briefly to allow a sufficiently accurate measurement.
• a stopped wire is cut with a vertical cut by means of a linearly movable cutting tool.
• the spring coiling machine is equipped with a camera-based optical measuring system for the non-contact, real-time acquisition of data on the geometry of a currently manufactured spring.
• the measuring system has a CCD video camera 250, which in the case of an example, at a resolution of 640 ⁇ 480 pixels (picture elements), can deliver up to 90 frames per second via an interface to a connected image processing system.
• the image acquisition of the individual images is triggered in each case via trigger signals (trigger) of the controller. This determines the measurement times.
• the software for image processing is housed in a program module, which cooperates with the control device 180 of the spring coiling machine or is integrated in this.
• the camera is fastened on a torsion-resistant carrier rail 255, which is mounted laterally next to the cable guide device in the region of the guide rollers of the feed device on the machine frame of the spring-loaded winch. is attached so that the longitudinal axis of the support rail parallel to the machine axis 1 18 extends.
• the measuring camera is longitudinally displaceable on the carrier rail and can be fixed to arbitrary longitudinal positions. A stepless adjustment in height is also possible.
• the optical axis of the camera optics is in the example, approximately at the height of the central axis of the coil spring (i.e., at the level of the axis 1 18) arranged and perpendicular to this axis.
• a second camera 260 is intended for detection of the free spring end 204 and is therefore positioned on the carrier rail such that the free spring end runs into the detection range of the second camera in the final phase of the production of the helical spring.
• a lighting device is mounted, which flashes in response to triggering signals (triggers) of the control at the measuring times specified by the control and permits measurement in transmitted light.
• a reflected-light illumination device may be provided in order to improve the visibility of interesting details of the spring for the measurement.
• the machine axes of the CNC machine associated with the tools are controlled by a computer numerical controller 180 which has memory devices in which the control software resides, to which i.a. an NC control program for the working movements of the machine axes heard.
• This control device also controls the components of the measuring system.
• the forming tools When setting up the spring coiling machine, the forming tools are brought into their respective basic positions.
• the NC control program is created or loaded, which controls the positioning movements. controls the tools during the manufacturing process.
• the geometry input is made in the spring coiling machine by an operator on the display and control unit 170, which is connected to the control device 180.
• a programmable logic controller (PLC) is realized, which works cycle-oriented.
• the drive positions of the machine axes are precalculated by the CNC control.
• the programmable logic controller is responsible for the outputs and inputs and operates after a fixed time frame or after a fixed cycle. Typical cycle times are often in the range of one hundredth of a second. In the example, the cycle time of the controller is 8 ms (milliseconds).
• the inventors have recognized that significant measurement errors can occur if the trigger signals (triggers) for the measurements are directly coupled to the cycle times of the PLC. A recognized problem will be explained in more detail with reference to FIG.
• the defined time interval of the PLC with a sequence of cycles of the same duration (cycle time At z eg 8 ms) is plotted on the time axis (x-axis).
• the y-axis denotes the feed path V of the wire conveyed by the feeder.
• the corresponding times in the control program are calculated in advance when setting up the machines or when creating the CNC control program.
• the cutting times do not coincide with the cycle times of the PLC.
• the production time At F which is required for the completion of a spring, is not an integer multiple of the cycle time At z . This results in measurement problems. If a measurement is triggered, if the cutting tool is already in contact with the wire or even has already separated the spring, no reliable measurement is possible. The measurement time should therefore be earlier than the time of the cut. However, if the measuring point is too far before the cutting time, the spring is not yet completely finished, so that measurement errors result, for example in the form of an incorrect value for the spring length or the end position of the spring end.
• the measuring error MF1 is particularly large when measuring the first spring F1, since the last possible measuring time, which coincides with the cycle time of the PLC (vertical dashed line), is almost a complete cycle time before the cutting time.
• the resulting measurement error MF6 is significantly smaller, since the cutting time is only about half a cycle or a few milliseconds (about 3 to 4 ms) after the immediately preceding cycle time (vertical dashed line).
• this method of measurement can result in considerable measurement errors, which as a rule also vary from spring to spring. Due to the time offset measurement errors caused by the fact that the length of the spring continues to increase until cutting due to the ongoing wire feed. The resulting measurement error is usually so large that sorting errors can occur and a control is no longer possible reliably lent. As shown schematically, the jitter can amount to several milliseconds.
• a trigger signal (trigger signal) of the controller measuring time of the measuring system is synchronized with the numerically controlled movements of the machine axes of the spring coiling machine with a temporal accuracy significantly larger is as the cycle time At z of the control of the spring coiling machine.
• trigger signals can be generated for the measuring system at measuring times which lie between cycle limits or between the cycles of the programmable controller, ie within one cycle.
• the programmable logic controller is equipped with a special output card which, with the aid of time stamps, can also control the output for the trigger signal of the camera between the PLC clock cycles. Suitable output cards are commercially available. For example, an output card from the field of laser technology with an accuracy of about 1 ps can be used.
• the outputs of the PLC can also be set between the cycles.
• the necessary control commands for the trigger signal are inserted based on the programmed spring geometry. Depending on the camera system used, they can then be adapted automatically. This makes it possible to position the trigger signal or the measurement time in the course of the spring production so accurately that the images can be taken immediately before placing the cutting blade on the wire. Targeted feedback can be used to control the tool positions
• FIGS. 3 and 6 A typical sequence of a measuring process immediately before the flying rotating section will be explained in more detail with reference to FIGS. 3 and 6.
• the rotationally driven cutting tool 152 is shown at three consecutive times immediately before and during the cutting engagement.
• the cutting tool approaches the passing wire 15 in an accelerated motion.
• the cutting tool is just setting on the wire, the cutting process begins.
• the cutting tool has completely severed the wire and has reached its lower reversal point on its round trajectory.
• FIG. 6 shows in the upper part of a figure a speed-time diagram of the feed speed V z of the wire feed. After an initial acceleration phase, the wire feed speed remains constant during the production of many successive springs and is shut down only after completing a series of springs.
• the speed-time diagram in the lower part of the figure shows the moving speed V s of the cutting tool during the continuous wire feed.
• the vertical dashed lines indicate in each case the times t 2 , to which the cutting tool touches down on the wire and the cut begins.
• the cutting tool does not rotate uniformly, but undergoes a cyclic movement with acceleration phases and deceleration phases, wherein the cutting tool is accelerated in the direction of wire before the cut and is retarded to a very low speed of movement after the cut.
• the cutting tool is usually constantly in motion, although between the individual cuts, the movement speed is very low. As a result, jerk-free operation is achieved with relatively low energy consumption.
• the measuring time point t M determined by means of the time stamping method or the associated narrow time window lies immediately before the intervention of the cutting tool in the wire, for example between the times ti and t 2 in Fig. 3.
• the full length of the finished spring is practically achieved, so far as measuring errors are reduced to a minimum.
• the measured spring length corresponds to the actual spring length of the finished spring within the scope of the measurement accuracy.
• a very reliable sorting of the springs with regard to the criterion spring length is possible.
• the performance of certain springs can be approximately doubled compared to conventional standing cut systems.
• the energy consumption per spring drops by up to 40% and the quality of the springs increases.
• significantly lower loads on the mechanics and thus higher stability result.
• the invention can be implemented with different measuring systems and for different measuring methods. A suitable method is described in DE 10 2010 014 385 A1 of the applicant. The measuring times can be determined there as described in the present application.

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• 2012
  • 2012-03-21 DE DE102012204513A patent/DE102012204513B3/de active Active
• 2013
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  • 2013-03-07 CN CN201380026626.3A patent/CN104487186B/zh active Active
  • 2013-03-07 WO PCT/EP2013/054604 patent/WO2013139612A1/de active Application Filing
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