Patent Application
20190217357
This application claims priority from EP application serial No. 18152097.4 filed on Jan. 17, 2018.
The present invention relates to a pressing machine, in particular a hand-held pressing machine, for pressing tubular workpieces, and a method for operating a pressing machine.
In the prior art, methods for pressing tubular workpieces, in particular pipes in installation technology, are known. In a known method, two pipes are non-detachably connected to one another by means of a press fitting. For this purpose, the pipes or tubes are inserted into openings of a press fitting which has polymer seals for sealing with the pipes. After insertion of the pipes to be joined, the press fitting is pressed by means of a suitable pressing machine, and plastically deformed so that the pipes can not be pulled out from the fitting and the seal seals securely.
The pressing is carried out with a hand-held and motor-driven pressing tool, which can have interchangeable tools, such as press jaws of different sizes and geometries. In addition, pressing tools are also known for other tasks, for example pressing tools are used for pressing, crimping or cutting workpieces, for example in the electrical industry.
In a hand-held press machine, the press jaws are placed around the press fitting for compression. When closing the pressing jaws, a force is exerted on the surface of the press fitting, so that the fitting is compressed and thereby plastically deformed, whereby the workpieces are securely joined together. Here, the inner tubes or pipes can undergo plastic deformation.
The pressing process is terminated in press machines of the prior art usually characterized in that when a certain maximum pressure is reached, a pressure relief valve is opened. The specified maximum pressure ensures that a suitably high pressing force has been exerted on the workpiece in order to ensure sufficient compression.
Thus, EP 2 501 523 B1 discloses a hand-held pressing device for pressing a press fitting in installation technology and for pressing cable lugs. To generate the required high pressing forces, the pressing tool is connected to an electro-hydraulic conversion device. The drive motor is a brushless electric motor. As soon as the required pressing force is reached, a pressure relief valve opens and the engine speed increases abruptly. This is detected by a control of the pressing device and the electric motor subsequently switched off.
However, the termination of the pressing operation by means of a permanently set pressure relief valve has the disadvantage that upon reaching the maximum pressure, the pressing jaws of the pressing tool already abut each other and no further deformation on the workpiece can take place. The fitting was previously compressed as much as possible during the pressing process and can no longer experience further plastic deformation. The direct pressing together of the dies leads naturally to a strong wear on the tool, the power transmission parts and the drive motor. In addition, unnecessary electrical energy is consumed.
It is therefore an object of the present invention to provide a press machine which overcomes the above problems and achieves a secure and durable press fit between tubular workpieces without causing unnecessary wear on the press machine and unnecessary power consumption. Furthermore, a corresponding method for operating a pressing machine is to be provided.
In one aspect, the present invention provides a pressing machine for plastically deforming a workpiece. The pressing machine comprises a motor, pressing jaws which are driven by the motor and can apply a force to the workpiece during operation, and a power transmission unit coupled to the motor and the pressing jaws for transmitting power from the motor to the pressing jaws. The pressing machine also comprises at least one sensor unit for measuring at least one pressing parameter (P), and a controller which receives a currently measured value of the press parameter from the sensor unit and determines therewith a slope of a press parameter curve (K) of the press parameter (P). The controller terminates a pressing operation before reaching a maximum possible pressing force (Pmax) when the slope of the press parameter curve (K) of the pressing parameter (P) fulfills a switch-off criterion.
In another aspect, the present invention provides a method of operating a pressing machine for plastically deforming a tubular workpiece. The method comprises the following operations engaging the workpiece with pressing jaws of the pressing machine. The method also comprises starting a motor of the press machine to apply a force through the press jaws to the surface of the engaged workpiece. The method further comprises measuring a value of a press parameter (P). The method additionally comprises receiving a currently measured value of the press parameter (P) by the controller, and thereby determining a slope of a press parameter curve (K) of the press parameter (P). The method also comprises stopping the motor from reaching a maximum possible pressing force (Pmax) of the pressing machine by the controller when the controller detects that the slope of the press parameter curve (K) of the pressing parameter (P) is on switch-off criterion fulfilled.
The difficulties and drawbacks associated with previous approaches are addressed in the present subject matter as follows.
As will be realized, the subject matter described herein is capable of other and different embodiments and its several details are capable of modifications in various respects, all without departing from the claimed subject matter. Accordingly, the drawings and description are to be regarded as illustrative and not restrictive.
Hereinafter, preferred embodiments of the present invention will be illustrated with reference to the accompanying drawings.
At least one of the above problems is solved according to the invention by a pressing machine and a method for operating a pressing machine as described herein.
In particular, at least one problem is solved by a pressing machine for plastically deforming a tubular workpiece, in particular a fitting, wherein the pressing machine has a motor, and pressing jaws, which are driven by the motor and can apply a force to the workpiece during operation. The pressing machine also has a power transmission unit, which is coupled to the motor and the press jaws for transmitting a force from the motor to the pressing jaws. The pressing machine also has at least one sensor unit for measuring at least one pressing parameter, and a controller which receives the currently measured value of the pressing parameter from the sensor unit utilizing a slope of a press parameter curve of the determined press parameter. The controller terminates a pressing operation before reaching a maximum possible pressing force when the slope of the press parameter curve of the press parameter meets a shutdown criterion.
In the present invention, the slope, i.e., the rise of a press parameter curve, is monitored, which results during the pressing process. The increase is characteristic for the increase of the pressing force on the workpiece with progressive pressing process. If the workpiece has reached the maximum deformation at the end and the pressing jaws of the pressing machine are completely closed, further increase in pressure results only in an elastic deformation of the pressing jaws. In this case, a purely linear increase in the values of a pressing parameter can be detected, e.g. in a hydraulic pressing device a purely linear increase in the pressure-time curve or current-time curve. This characteristic increase at the end of the pressing process is used by the controller to turn off the engine of the pressing machine before reaching a maximum possible pressing force and thus to end the pressing process.
The automatic termination of the pressing process before reaching the maximum possible pressing force of the machine due to the evaluation of the slope of at least one press parameter curve prevents further unnecessary pressing together of the pressing jaws, resulting in a reduction of the load and wear of the pressing jaws and other parts of the machine and saves energy and/or time. An additional interaction of a user to end the pressing process is not necessary.
The comparison of the slope of the press parameter curve of the measured values of the at least one pressing parameter with a switch-off criterion automatically takes into account the properties of the workpiece to be pressed, for example the material, the size, the design, etc. Thus, information or details of these properties is not required nor necessary before the respective pressing process. The switch-off criterion is independent of the individual properties of the workpiece to be pressed. Due to the monitoring of the slope of the press parameter curve, the controller can reliably finish the pressing operation after the plastic deformation of the workpiece, regardless of the level of the pressing force from which no further plastic deformation of the workpiece occurs.
During evaluation, one or more pressing parameters can be taken into account in any combination. The consideration of several pressing parameters at the same time strengthens the robustness of the analysis compared to so-called leaks, due to redundancy and/or random deviations.
Various sensors for measuring the same or different pressing parameters can be used for the evaluation with the present control.
The respective switch-off criterion can be adapted to the respective process parameter or to a combination of the process parameters.
Preferably, the switch-off criterion indicates that, with a continuation of the pressing process, only an elastic deformation on the pressing jaws occurs. This is the case when the pressing jaws are completely closed and no plastic deformation of the workpiece occurs. The switch-off criteria are preferably predetermined values of the slope for a specific press parameter curve, on the basis of which the controller can automatically decide when the current pressing operation is terminated.
Preferably, the power transmission unit is a hydraulic system and the sensor unit is a pressure sensor which measures the pressure in the hydraulic system as a press parameter. This makes it easy to adapt the control according to the invention to existing electro-hydraulic press machines. Via a pressure sensor, the hydraulic pressure can be measured simply and reliably as a process parameter and provided to the controller. The hydraulic pressure is directly proportional to the force applied to the tool pressing force, so that reliable determination of the force curve on the pressing jaws is possible via the hydraulic pressure.
If the power transmission unit is preferably a mechanical system, the sensor unit is a force sensor which measures the force at a location in the mechanical system as a press parameter. The control of the present invention can also be applied to pressing devices with a purely mechanical power transmission. In mechanical press machines, a force is transmitted from an engine to the press jaws via one or more power transmission units. In this case, the occurring force can be measured at different locations in the mechanical system. For this purpose, conventional load cells, strain gauges or similar sensors can be used. The measured force is usually also directly proportional to the pressing force applied to the tool, so that a reliable determination of the force curve on the pressing jaws is possible via the force measurement.
Preferably, a current flowing through the motor can continue to be used as the pressing parameter. This current can be measured by means of the controller, which then preferably also assumes the task of the sensor unit. From the current flowing through the motor, the force curve can also be derived at the press jaws.
Preferably, the control terminates the pressing process only when, in addition to the switch-off criterion, a predetermined minimum value for a pressing parameter (P) has been exceeded and/or when the duration of the pressing process has exceeded a minimum time. This does not take into account start-up effects at the beginning of the pressing process or areas of the pressing process in which a plastic deformation of the workpiece regularly takes place. This reduces the risk of incorrect measurements and an unwanted premature termination of the pressing process. Reliable compression of a workpiece usually requires a minimum pressing force achieved, so that no automatic termination of the pressing process should take place under this minimum pressing force.
Preferably, the slope of the press parameter curve indicates the time profile of the values of a press parameter and is preferably formed from the current and the time-preceding value of the press parameter. The consideration of the time profile of a press parameter is simply possible in the form of a time series, in particular if the slope of the process parameter curve is calculated from temporally successive measured values. Considering the current and previous value to determine the slope is simple and can be quickly implemented in a computational manner so that results can be real-time. Thereby, an immediate, timely control in response to the evaluation can be achieved. The significantly constant, linear course of the press parameter curve in the direct pressing together of the pressing jaws at the end of the pressing process, enables a robust and automatic detection of this pressing state.
Preferably, the controller may also have a database in which shutdown criteria for certain pressing jaws and/or workpieces are stored. The shutdown criteria here are preferably digital values of the slope of the process parameter curve in which an automatic shutdown is to take place. The database may contain values for shutdown criteria, which may depend on the properties of the press jaws used, such as material, size, type, etc.
Preferably, the pressing machine is an electrically driven hydraulic or mechanical hand pressing device for pressing tubular workpieces. With the help of a hand pressing device, pressings can be used flexibly at various locations, such as a construction site. In this case, electrically driven hand presses can apply high pressing forces, which ensure reliable pressing. In a hydraulic hand pressure device, for example, during operation, a hydraulic pressure up to about 550 bar can be applied, which acts directly on the workpiece enclosed by the pressing jaws.
At least one of the above-mentioned problems is also solved by a method for operating a pressing machine, for plastically deforming a tubular workpiece, in particular a fitting, the method comprising the following steps in the order given:
Preferably, the pressing parameter is a pressure, a force, or a current through the motor, or any combination of these parameters. These parameters are characteristic of the pressing pressure of the pressing machine.
The motor is preferably stopped only when, in addition to the switch-off criterion, a previously defined minimum value for a press parameter has been exceeded and/or when the duration of the press process has exceeded a minimum time.
Preferably, the method comprises the step of reading at least one switch-off criterion from a database of the controller. The switch-off criterion can be stored in a database in the control of the press machine and read, for example, suitable for the press jaws used and used in the control.
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
The piston pump 27 pumps to move a hydraulic fluid from a reservoir into a working cylinder 25, whereby the hydraulic pressure in the working cylinder 25 increases. The increasing hydraulic pressure pushes a piston 28 movably guided in the cylinder in the illustration of
The piston 28 is mechanically connected to rollers 29, which move with the movement of the piston 28. The rollers 29 move in a conventional manner between inclined ends of pressing jaws 30, which are thus closed and can plastically deform the workpiece with high force. In operation, this transfers the hydraulic pressure directly proportional to the connected pressing jaw 30, and generates a pressing force F directly proportional to the hydraulic pressure on the workpiece. The pressure on the workpiece is directly proportional to the hydraulic pressure.
As a result of the increasing hydraulic pressure P during pressing and the thus increasing pressing force F on the workpiece or the fitting, the workpiece is pressed and plastically deformed. By measuring the hydraulic pressure P, the pressing force F on the tool can be determined.
The hydraulic pressure P in the hydraulic system 26 can be easily measured by means of a pressure sensor 42. The pressure sensor 42 communicates the measured pressure signal to the controller 40 via signal lines or wirelessly by means of a corresponding radio transmission. Wireless signal transmission means, such as common digital wireless connections such as e.g. Bluetooth, NFC or the like can be used. Analog signals from the pressure sensor 42 can be converted into digital signals in an A/D converter so that they can be evaluated by the digital controller 40.
The controller 40 has for this purpose at least one digital processing unit, such as a microcontroller, DSP, FPGA, ASIC or the like. In addition, the control unit may have a database (not shown) stored on data storage devices in which predetermined values required for the evaluation can be retrieved.
Depending on the evaluation results, the controller 40 via control electronics (not shown) generates corresponding control signals to the motor 20. The motor 20 is controlled by means of these control signals to operate at a certain regulated speed and stop at the end of the pressing process.
In another embodiment, not shown, the pressing machine may also be designed as a purely mechanical hand pressing device with a mechanical power transmission unit. In a mechanical hand press, a motor generates a rotational movement, which is transmitted via a transmission to at least one mechanical power transmission unit, for example a lever or a screw drive. The mechanical power transmission unit converts the rotary motion into a linear motion which, in accordance with the hydraulic hand press apparatus 10 of
Force sensors, for measuring the force F transmitted to the tool by the motor, may be located at various locations in the mechanical hand press to measure a force proportional to the pressing force F and to signal the force to the controller.
Furthermore, the current absorbed by the motor 40 also behaves proportional to the motor torque and thus to the pressing force F on the pressing jaws.
The press parameter curve K3 was recorded during the compression of a fitting made of a second material. The material of this fitting had a greater strength than in curve K2 and is stainless steel in one embodiment.
In
The curve of the press parameter curve K2 shows an earlier hydraulic pressure increase than the press parameter curve K1, since there is a fitting made of a soft material between the press jaws. From the time T1K2 the press parameter curve K2 in turn increases linearly, since at this time the actual pressing process is completed, the fitting was completely plastically deformed and the pressing jaws are completely closed and rest against each other. The linear increase ΔTK2 occurs with a substantially same slope as that of the curve K1. When the maximum pressure PmaxK2 is reached, the overpressure valve opens again at the time T2K2 and the curve K2 drops very quickly to a minimum pressure.
The press parameter curve K3 increases more than the press parameter curve K2 due to the harder material of the fitting to be pressed. Furthermore, a higher overall pressure must be applied to the curve K3 than to the curve K2 in order to close the pressing jaws and completely plastically deform the fitting. At time T1K3, the curve of K3 becomes linear, indicating the end of the actual pressing operation and signaling that the pressing jaws are completely closed and abutting one another. As can be seen, the slope of the linear region ΔTK3 substantially corresponds to the slope of the linear regions ΔTK1 and ΔTK2. This slope of the press parameter curve is therefore a characteristic measure of the end of the actual pressing process on the workpiece.
As can be further seen from
The curves K1, K2 and K3 would be correspondingly given if, instead of the hydraulic pressure over time, a force acting mechanically in the system or the current through the motor 20 were plotted over time. Again, from a linear increase of the curve with a characteristic slope, the end of the pressing process and the juxtaposition of the pressing jaws can be seen.
The shutdown of the motor 20 can be made dependent on the controller 40 in addition to other conditions, such as to detect outliers of a press parameter curve and exclude such. Thus, in addition to the switch-off criterion, it may be necessary for a switch-off of the motor 20 if a previously defined minimum value for a pressing parameter P has been exceeded and/or if a duration of the pressing process has exceeded a minimum time Tmin.
In the example of the curve K2 of
However, it is also possible to specify a minimum time Tmin which the pressing process must take at least before the controller can switch off the motor 20.
From time T1K2, the slope value determined by the controller 40 coincides with a predetermined slope value stored in the database of the controller 40 as the switch-off criterion. From this point in time T1K2 on, the controller 40 then preferably determines the number of rise values which are the same in a time range.
At the later time T3K2, a predetermined number of increases with equal slope values were then counted. The counted rise values are essentially the same as the predefined rise value stored in the database. Permissible tolerances of the slope values can be determined empirically and stored in the controller 40.
In the example of
In
From
Many other benefits will no doubt become apparent from future application and development of this technology.
All patents, applications, standards, and articles noted herein are hereby incorporated by reference in their entirety.
The present subject matter includes all operable combinations of features and aspects described herein. Thus, for example if one feature is described in association with an embodiment and another feature is described in association with another embodiment, it will be understood that the present subject matter includes embodiments having a combination of these features.
As described hereinabove, the present subject matter solves many problems associated with previous strategies, systems and/or devices. However, it will be appreciated that various changes in the details, materials and arrangements of components, which have been herein described and illustrated in order to explain the nature of the present subject matter, may be made by those skilled in the art without departing from the principle and scope of the claimed subject matter, as expressed in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| EP 18152097.4 | Jan 2018 | EP | regional |
