Patent Application
20200086581
The invention concerns a method and a device for quasi-simultaneous laser transmission welding of plastics.
Methods for welding plastics by means of a laser are known from the state of the art. In laser transmission welding, one of the joining partners to be joined or welded is highly transparent to laser beams, while the other joining partner has a high degree of absorption in relation to the laser beam. Thus, the laser beam traversing one joining partner provides local heating at the joint located between the two components. The pressure required for welding is built up in the familiar way by pressing both joining partners together.
Such a laser transmission welding method is described, for example, in DE 10 2004 004 985 A1 and WO 2007 082 992 A1, whereby the laser beam is guided by means of an arrangement comprising several mirrors onto the joining partners to be welded according to both publications.
In such known methods, movable mirrors are usually used, which are equipped with a so-called galvanometer drive. This is often abbreviated as galvo or galvo mirror, which is why known devices of this kind are also known as galvo scanners. Such mirrors with galvanometer drive as well as their use in devices and methods for quasi-simultaneous laser transmission welding of plastics are well known from the state of the art.
The course of the laser beam in such methods is limited in such a way that, seen from the laser, it is always directed by a last mirror arranged in the beam path onto the plastics or joining partners to be welded. Although this mirror can be swivelled by the galvanometer drive, it cannot otherwise change its spatial position. This limitation result in some disadvantages.
For example, beam shading can occur due to high component walls or other sections of one of the joining partners.
Furthermore, existing connections, which are arranged next to or above the weld seam, can lead to beam shading.
In addition, convex components, for example, can have very unfavorable angles of incidence of the laser beam or unfavorable angles between a component surface and the incoming laser beam.
Without addressing the aforementioned disadvantages, the EP 1 048 439 A2 and the EP 2 255 952 A1 propose to arrange the beam output, from which the laser beam emanates, on a robot arm of a well-known articulated arm robot. However, as was also recognized in EP 2 255 952 A1, such an arrangement poses the problem that the robot cannot achieve high speeds.
However, very high speeds are required for quasi-simultaneous laser transmission welding because the laser beam is deflected so quickly between the welding types or guided along the weld seam that the plastic is heated and plasticized simultaneously at all welding types and welding is thus carried out simultaneously at virtually all welding types.
The EP 2 255 952 A1 proposes once again the familiar galvo scanner as an alternative to a beam output provided on the robot arm in order to achieve high speeds. However, this leads to the disadvantages already described.
The task of this invention is to overcome the disadvantages arising from the state of the art. In particular, a method and a device for quasi-simultaneous welding of plastics and quasi-simultaneous laser transmission welding shall be provided, which achieve high speeds as well as overcome the limitations of known galvo scanners.
The objects of independent claims and details disclosed herein lead to the solution of the task.
Advantageous embodiments are also described herein and in the subclaims.
The present invention proposes a method for quasi-simultaneous welding of plastics on at least two types of welding location by means of a laser beam (laser transmission welding), whereby the laser beam emanates from a laser optics, which is assigned to a platform of a delta robot and is guided by a movement of this platform.
The plastics or plastic parts to be welded can also be referred to as joining partners.
Delta robots are known from the state of the art and are described below with regard to the inventive device. Thanks to their parallel kinematics, which are explained in more detail below, delta robots can, for example, run contours much faster than articulated robots or other robots.
In the context of this invention, a welding location is, for example, a spot on a weld seam. Preferably, a welding seam is created with the welding method according to the invention. A weld seam always consists of a large number of welding points or can be thought of as a sequence of a large number of individual welding points.
The laser, i.e. the device for generating the laser beam, can be arranged on the platform. In order to make the platform as light as possible, however, the laser is preferably mounted at a different location, for example on a base plate of the delta robot, and is connected to the laser optics via an optical conductor.
In the context of this invention, laser beam guidance is defined as any measure that changes the spatial orientation or spatial course of the laser beam or moves the laser beam. Usually, at least the laser optics are moved for this purpose. However, it can also be considered that movable mirrors deflect the laser beam and thus change its spatial course.
Details are given with regard to the device that was invented.
It can be thought that the laser beam is guided by a combination of the movement of the platform and another movement, which is caused by a motion device assigned to the platform.
Numerous devices can be considered as motion devices. In principle, any device can be considered which is suitable for influencing the spatial orientation of the laser beam. Details are explained with regard to the device in accordance with the invention.
It may be thought that at least one subunit of the motion device is moved relative to the platform to cause further movement. This at least one subunit may, for example, be at least one mirror which is pivotally mounted opposite the platform. A galvo mirror can be thought of here. Furthermore, this at least one subunit can be an element rotatably fixed to the platform on which the laser optics can be fixed or arranged. Both variants are explained below.
In the context of the present invention, a rotatable fixing, as well as a pivotable fixing and a rotatable fixing, is understood to be a fixing which enables the execution of a rotational movement of the respective component.
It can also be thought that at least one subunit is moved by a shaft. In this case, the drive may be located outside the platform to make the platform as light as possible, as will be explained in more detail below in relation to the device.
As mentioned above, it can be thought that the laser beam is deflected by at least one mirror, which is arranged so that it can pivot relative to the platform. Preferably, the at least one mirror is arranged so that it can pivot relative to an imaginary plane within which the platform essentially lies.
Here different swivel movements can be thought of. Preferably, however, a pivoting movement is preferably understood as a rotation, whereby the axis of rotation lies within the aforementioned imaginary plane or is orthogonal to it.
Furthermore, it can be considered to provide several of the above described swivelling mirrors. In particular, two mirrors should be provided. The pivot and rotation axes of these mirrors are preferably arranged orthogonally to each other. The mirrors are preferably arranged in such a way that the laser beam leaving the laser optics is first reflected by a first mirror, whereby the reflected laser beam from this mirror is then reflected by a second mirror. The beam from the second mirror is preferably directed onto the workpieces to be welded. The spatial orientation of the laser beam can be influenced by corresponding rotation or tilting of both mirrors around their axes of rotation in order to reach welding points at a distance from each other.
As already mentioned, the laser optics can be mounted so that it can move relative to the platform to guide the laser beam. For this purpose, the laser optics can be fixed to an element, which in turn is rotatably fixed to the platform. Such an arrangement is to be seen in particular as an alternative to the arrangements described above, comprising at least one mirror.
It can be thought of that a temperature of the plastic is measured by means of a pyrometer, whereby a measuring result is used for the evaluation and/or regulation of the procedure. Here the temperature of the plastic is measured preferably in the area of the welding points or the welding seam.
The temperature can be measured either continuously or at certain times in intervals.
If, for example, it is known which temperature the welding points or the welding seam must have in order to achieve the desired welding success or the condition of the welding seam lies within the desired limits, it can be easily determined by measuring the temperature by means of the pyrometer when the welding method can be terminated. The measured temperature is used directly to control the method. The measured temperature can also be used in any other way to control the method.
Furthermore, the measured temperature, alternatively or complementary, can also be recorded for an evaluation of the method. By measuring the heating of the weld seam over a large number of welding processes and storing the corresponding data, it is possible, for example, to determine at a later point in time within the framework of a comparison whether certain problems occurred during welding or whether certain components have to be sorted out as rejects. The measured temperature can be used in any way for an evaluation.
This invention also includes a device for quasi-simultaneous welding of plastics, comprising a Delta robot with a platform, with laser optics assigned to the platform. This is therefore a device for quasi-simultaneous laser transmission welding.
Delta robots are state-of-the-art parallel kinematic machines. They are used, for example, for handling small objects at high speed. For the structure and function of delta robots, please refer to U.S. Pat. No. 4,976,582.
Delta robots comprise a movable platform, which can be connected to a base plate via three arms, for example. Usually the base plate accommodates a rotary drive for each arm. The arms only comprise struts and passive joints, so they are only moved by the rotation of the respective drive.
The platform of the delta robot is preferably used to guide the laser beam emanating from the laser optics, which has already been described above with regard to the procedure according to the invention.
In the context of this invention, laser optics is understood to mean an arrangement comprising at least one optical component. For example, collimators such as collimator lenses can be considered. Furthermore, components for focusing, e.g. corresponding lenses, can be considered. Alternatively, appropriately curved mirrors can also be considered, which cause collimation and/or focusing. Usually, the laser beam originates from a focusing component which is preceded by a collimator.
The laser, i.e. the component that generates the laser beam, can be arranged on the platform of the delta robot. In order to keep the weight of the platform as low as possible, however, the laser is preferably positioned elsewhere, for example, it can be attached to the base plate. In this case, instead of the entire laser, only the laser optics are arranged on the platform of the delta robot and are connected to the laser via an optical conductor, for example.
The device can therefore be designed in such a way that the platform is assigned a first end of an optical conductor which is connected to the laser optics, whereby a second end of the optical conductor is connected to a laser, whereby this laser is arranged outside the platform.
The optical fibre does not interfere with the movements carried out by the Delta robot platform and the arrangement only slightly increases the weight of the platform, allowing the light platform to perform rapid movements.
The laser optics can be fixed to an element that is rotatably fixed to the platform. It may also be remembered that this element is not fixed directly to the platform but via a second element, the first element being rotatably fixed to the second element and the second element being rotatably fixed to the platform. Such an arrangement can be conveniently provided by a gimbal suspension. The cardanic suspension is a subassembly of a motion device which is capable of influencing the spatial course of the laser beam by its movement. In this case, the motion device can also include drives for the pivot bearings of the gimbal suspension. In addition to a cardanic suspension, other motion devices can also be considered, which have at least one subunit that can be moved relative to the platform in order to influence the spatial course of the laser beam.
By influencing the spatial course of the laser beam both by the movement of the platform and by the further movement caused by the motion device, i.e. that of the subunit, the laser beam can be aligned according to the situation, which was not possible to this extent with known devices for laser transmission welding of plastics.
In particular, the gimbal suspension allows a high degree of freedom of movement for the laser optics, which in turn means that the laser beam can be guided very flexibly in its spatial course.
As an alternative to gimbal suspension, it can be thought of to provide at least one mirror that can be swivelled relative to the platform. Here, for example, an optical arrangement comprising at least one such mirror represents the motion device, with the swivelling mirror representing the subunit. This at least one pivoting mirror serves to reflect the laser beam. It is preferably attached to the platform in a pivotable manner. This can be at least one galvo mirror.
It can be thought of to provide two mirrors pivotable relative to the platform, whereby the laser beam from the laser optics is first reflected at a first mirror and then at a second mirror before it is directed to the welding points or the welding seam. Here it can be considered to arrange the pivot and rotation axes of the mirrors orthogonally to each other in order to be able to effect a wide spectrum of possible spatial orientations of the laser beam.
Numerous other motion devices and subunits can be considered. As explained above using the examples, the subunit is preferably suitable for influencing the spatial course of the laser beam via rotation relative to an imaginary plane within which the platform lies.
A combination of a rotatable element fixed to the platform and a pivoting mirror is also conceivable. For example, the laser optics can be mounted on an element that is fixed to the platform in such a way that it can rotate about an axis relative to the platform. A mirror may also be provided which is rotatable relative to the platform about an axis orthogonal to the axis of rotation of the aforementioned element. Depending on one degree of rotation or deflection of the element with respect to the platform, the laser beam hits another part of the mirror. Again, depending on the degree of rotation of the mirror, the laser beam is reflected differently. By such an arrangement the same result or coverage can be achieved as by an arrangement comprising two mirrors or a cardanic suspension as described above.
The at least one sub-unit, for example the rotatable element described above or the mirror described above, shall be connected to a drive to be moved. In order to keep the weight of the platform as low as possible, it may be advisable not to place these drives on the platform but to connect at least one subunit to the drive via a shaft. It may therefore be thought that at least one shaft is provided, a first end of the shaft being associated with the rotating element or mirror, capable of causing the rotating element or mirror to move, a second end of the shaft being associated with a drive located outside the platform.
The drive may be attached to the base plate or to another location.
The device may include a pyrometer the function of which has already been described in relation to the invention.
The pyrometer may be associated with or attached to the platform. For example, the pyrometer may be used in laser optics.
In order to keep the weight of the platform as low as possible, the pyrometer can also be mounted elsewhere, for example on the base plate. Here, the pyrometer can be connected to one end of an optical fiber, the opposite end of which is fixed to the platform in order to feed the radiation to be measured to the pyrometer.
This can be the same optical fiber that connects the laser outside the platform to the laser optics, or a separate optical fiber.
It should be noted that this invention also includes a system consisting of at least one delta robot as described above and may also include, for example, a pyrometer, at least one drive for the subunit, and other components not attached to the delta robot.
In order to keep the weight of the platform as low as possible, it may be considered that the laser optics comprise half inch components. Half-inch components include, for example, half-inch optics with dimensions of about 12.7 mm.
It can also be considered to manufacture all components of the platform and all components arranged on it from materials that are as light as possible, such as fiber composite materials or other fiber composite materials, in order to save weight.
This invention also generally includes the use of a delta robot for quasi-simultaneous welding of plastics, in particular for quasi-simultaneous laser transmission welding.
Further advantages, features and details of the invention result from the following description of preferred execution examples as well as from the drawings; these show in:
The
The
A laser optic 2 is attached to platform 4, which is connected via an optical conductor 13 to a laser attached to the base plate 5 and not visible in the drawing.
The embodiment according to
With reference to
The well-known galvo scanner 9 according to
In the
In
In the arrangements according to
In the arrangement shown in
As shown in
Laser optics 2 can take the positions shown in
The same applies to the convex components 10, 11 in
As can be seen from
It should be noted that instead of moving the laser optic 2 relative to platform 4 as shown in
The forms of execution of the present invention shown in
The subunit 19, which in the arrangement shown in
By not placing the laser and drive 6 on platform 4, the weight of platform 4 can be kept as low as possible.
With respect to
In the form shown in
The rotation around the rotation axes 12.1, 12.2 is indicated by arrows. Cardanic suspensions and their function are sufficiently known from the state of the art. The rotation of the rings 16, 17 preferably takes place via one shaft each (not shown), so that the associated drive, which causes the rotation, does not have to be arranged on platform 4.
In the version shown in
The mirrors 15.1, 15.2. are preferably galvo mirrors.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2017 111 244.8 | May 2017 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/061965 | 5/9/2018 | WO | 00 |
