Patent Application
20220266422
The present disclosure relates to a changing station which enables a robot-supported grinding device to automatically change the grinding elements (i.e. grinding discs).
Grinding machines are frequently employed in industry and trade. Eccentric grinders are grinding machines in which a rotating movement around a rotational axis is superimposed on an oscillating movement (vibration). They are often used for the final machining of surfaces when high demands are placed on the surface quality, such as for spot repairs of surface defects on painted surfaces. In order to fulfill these demands, irregularities in the grinding process must be avoided as much as possible. In the field this is generally realized by having skilled professionals carry out these tasks in small batches.
In robot-supported grinding devices a grinding tool (e.g. an orbital grinding machine) is guided by a manipulator, for example, an industrial robot. In the process, the grinding tool may be coupled to the so-called tool center point (TCP) of the manipulator in various ways that enable the manipulator to adjust the tool to virtually any position and orientation. Industrial robots are generally position-controlled, which makes it possible to move the TCP precisely along the desired trajectory. In order to achieve good results from robot-support grinding, in many applications the processing force (grinding force) must be regulated, which is often difficult to realize with sufficient accuracy using conventional industrial robots. The moment of inertia of the large and heavy arm segments of an industrial robot is too large for a closed-loop controller to be able to react quickly to fluctuations in the processing force. To solve this problem, a linear actuator, smaller than the industrial robot, may be disposed between the TCP of the manipulator and the grinding tool in order to couple the TCP of the manipulator to the grinding tool. In this case the linear actuator only controls the processing force (that is, the application force between the tool and the workpiece), while the manipulator moves the grinding tool, together with the linear actuator, along the specifiable trajectory in a position-controlled manner.
Grinding machines such as, e.g. eccentric grinders, operate using thin, flexible and removable grinding discs which are attached to a backing pad. One very commonly used type of backing pads are the so-called daisy discs. A grinding disc is typically made of paper (or of a different fiber composite material) which is coated with abrasive particles and it can be attached to the carrier plate, e.g. by means of an adhesive layer, a hook and loop fastener or a Velcro fastener. Worn grinding discs are frequently changed manually, even in robot-supported grinding devices. Although a few concepts for robot-supported changing stations for changing grinding discs do exist, the known solutions are in general very complex and their realization is time-consuming and expensive.
The inventors identified a need for a changing station which makes it possible for a robot-supported grinding device to automatically change grinding discs in a relatively easy manner.
An apparatus for automatically removing a grinding disc from a grinding machine mounted on a manipulator is described herein. In accordance with one embodiment, the apparatus comprises the following; a bearing plate with a surface on which a grinding disc can be placed; a moveable clamping element which, in a first position, is elevated above the bearing plate; an actuator which is coupled to the clamping element and which is configured to move the clamping element into a second position in which the clamping element is pressed against the bearing plate such that the grinding disc is clamped in place between the bearing plate and the clamping element; and a release element which is arranged relative to the bearing plate such that the release element is actuated when the grinding disc is placed onto the surface of the bearing plate and is pressed against it. The release element and the actuator are (directly or indirectly, electrically or mechanically) coupled to each other such that, when the release element is actuated, the actuator moves the clamping element from the first position into the second position.
Further, a method for the automatic removal of a grinding disc from a grinding machine mounted on a manipulator is described herein. In accordance with one embodiment, the method comprises the following: Placing a grinding disc that is mounted on a grinding machine onto a bearing plate of a removal device by means of a manipulator, wherein, by placing the grinding disc onto the bearing plate, a release element of the removal apparatus is actuated. The method further comprises clamping the grinding disc in place between the bearing plate and a moveable clamping element which, in reaction to the actuation of the release element, is pushed into the direction of the bearing plate, and raising the grinding machine by means of the manipulator, by means of which the clamped grinding disc is removed from a carrier plate of the grinding disc.
In the following, various embodiments will be described in detail with reference to the illustrations in the figures. The illustrations are not necessarily true to scale and the embodiments described below are not limited to the aspects illustrated herein. Instead, importance is given to illustrating the basic underlying principles of the illustrated embodiments.
Before explaining various embodiments in detail, first a general example of a robot-supported grinding apparatus will be described. The example encompasses a manipulator 1, for example an industrial robot, and a grinding machine 10 with a rotating grinding tool (e.g. an orbital grinding machine), wherein the latter is coupled to the tool center point (TCP) of the manipulator 1 via a linear actuator 20. In the case of an industrial robot possessing six degrees of freedom, the manipulator may be constructed of 4 segments; 2a, 2b, 2c and 2d, each of which is connected via joints 3a, 3b and 3c (the first segment is usually rigidly attached to a base 41, which, however, need not necessarily be the case). Joint 3c connects the segments 2c and 2d. Joint 3c may be biaxial and allow a rotation of segment 2c around a horizontal axis of rotation (elevation angle) and around a vertical axis of rotation (Azimuth angle). Joint 3b connects the segment 2b and 2c and allows a swivel movement of segment 2b relative to the position of segment 2c. Joint 3a connects the segments 2a and 2b. Joint 3a may be biaxial and may (as in the case of joint 3c) allow a swivel movement in two directions. The TCP is at a permanent relative position in respect to segment 2a, wherein the latter usually also encompasses a rotational joint (not shown) which allows a rotational movement around a longitudinal axis of segment 2a (designated in
The manipulator 1 is usually position-controlled, i.e. the robot controller can determine the pose (position and orientation) of the TCP and can move it along a previously defined trajectory. When the actuator 20 comes to rest against an end stop, the pose of the TCP also defines the pose of the grinding tool. As previously mentioned, the actuator 20 serves to adjust the contact force (processing force) between the tool (grinding machine 10) and the workpiece 40 to a desired value during the grinding process. Controlling the force directly using the manipulator 1 is generally too inaccurate for grinding applications because the large moment of inertia of segments 2a-2c of the manipulator 1 renders it virtually impossible for conventional manipulators to quickly compensate force peaks (e.g. such as occurs when the grinding tool is placed on the workpiece 40). For this reason the robot controller is configured to adjust the pose of the TCP of the manipulator, while the force adjustment is carried out exclusively by the actuator 20.
As previously mentioned, during the grinding process the contact force FK between the tool (grinding machine 10) and the workpiece 40 can be adjusted with the aid of the (linear) actuator 20 and a force controller (which, for example, may be implemented in the controller 4) such that the contact force between the grinding tool and the workpiece corresponds to a specifiable target value. The contact force is in this case a reaction to the actuator force with which the linear actuator 20 presses against the surface of the workpiece. If contact between the workpiece 40 and the tool is absent, the actuator 20 comes to rest, due to the lack of contact force on the workpiece 40, against an end stop. The position control of the manipulator 1 (which may also be implemented in the controller 4) can operate completely independently of the force control of the actuator 20. The actuator 20 is not responsible for positioning the grinding machine 10, but instead only for the adjustment and maintenance of the desired contact force during the grinding process and for detecting a contact between the tool and the workpiece. The actuator may be a pneumatic actuator, e.g. a double-acting pneumatic cylinder. Other pneumatic actuators, however, may also be employed such as, e.g. bellows cylinders and air muscles. Direct electric drives (without transmissions) may also be taken into consideration.
If a pneumatic actuator is employed, the force can be adjusted in a conventionally known manner using a control valve, a controller (implemented in controller 4) and a compressed air reservoir. The specific implementation, however, is of little relevance for the remaining discussion and will therefore not be described here in further detail. As an alternative to the actuator 20 and depending on the application, a passive yielding element such as, e.g. a spring, may also be used. The actuator 20 may also be omitted if the manipulator itself is capable of providing force regulation of a satisfying quality.
The grinding machine 10 comprises a grinding disc 11 which is mounted on a backing pad 12. The surface of the backing pad 12 or the back surface of the grinding disc 11, or both surfaces, are configured such that the grinding disc 11 easily adheres to the backing pad 12 upon contact. For example, a hook and loop fastener or a Velcro fastener may be used to ensure that the grinding disc 11 remains adhered to the backing pad 12. One commonly used alternative to a hook and loop fastener is an adhesive coating on the backside of the grinding disc 11 which adheres to a corresponding surface of the backing pad 12.
As can be seen in
The actuation of the trigger element 33 (when the grinding disc is pressed against the bearing plate 35) triggers a mechanism that results in the edge of the grinding disc 11 being clamped in between the bearing plate 35 and a clamping plate 34. When the robot again moves the grinding machine 11 away from the removal device 30, the grinding disc 11 is held in place by the clamping plate 34, while the backing pad 12 of the grinding machine 10 is lifted away from the surface of the bearing plate 35. By raising the backing pad 12, the (clamped) grinding disc 11 is removed from the backing pad 12. In the following, an example of this described mechanism will be described in detail with reference to
As is illustrated in
The movement of the rocking lever 342 from the first position (clamp released) into the second position (clamp tightened) is triggered by the actuation of the trigger element 33. In the example illustrated in
In the example illustrated in
The aforementioned biasing force FB can be provided by various biasing mechanisms. In the example from
As previously mentioned, after clamping the grinding disc 11, the grinding machine 10 is again moved away from the removal device 30, by means of which the (clamped) grinding disc 11 is pulled off the backing pad 12. After this the rocking lever 341 (and with it the clamping plate 34) have to be moved back from the second position (clamp tightened,
Air can be blasted onto the grinding disc 11 at a high velocity through the compressed air nozzle 32, blowing it in the direction of the baffle plate 312 and onwards, e.g. into a container. The compressed air nozzle 32 and the baffle plate 312 are both optional, but in actual practice they can improve the robustness of the device 30. The reset mechanism (e.g. switching the compressed air from cylinder chamber V1 to cylinder chamber V2), as well as the blasting of compressed air out of nozzle 32, can be triggered by the robot controller (see
Some grinding discs stay adhered to the backing pad 12 (see
In order to verify whether the grinding disc removed from the grinding machine 10 has actually been transported away from the removal device 30, the removal device 30 may comprise a sensor 36. The sensor 36 can be seen in
It should be understood that the function of clamping the grinding disc 11 between the bearing plate 35 and the clamping element 34 (clamping plate) and of the trigger element 33 releasing the movement of the clamping element can be realized in other ways than as those illustrated in the example from
In general terms, the removal device comprises a bearing plate (see, e.g.
In the simplest of cases, the actuator may be a biased spring. A pneumatic actuator (pneumatic cylinder-piston unit) can also fulfill the same function as a biased spring when it is filled with compressed air. In some embodiments, the clamping element blocks, until it is actuated, the movement of the actuator (see
In other embodiments the actuator does not need to generate a biasing force while the movement of the actuator is mechanically blocked by the trigger element. Instead, the actuator is actively controlled to move the clamping element from the first position into the second position when the trigger element is actuated which, in this case, may also be an electric switch (e.g. a probe), which in turn is positioned such that it protrudes beyond the bearing plate and is thereby “automatically” actuated when the grinding disc mounted on the grinding machine is placed onto the surface of the bearing plate. In this case the actuator may be any given actuator (an electromotor, a linear motor, a pneumatic actuator, a solenoid, etc.) which is configured to move the clamping element from the first position into the second position. Instead of a simple switch like, e.g. a probe, a different sensor element may also be used which is capable of detecting that a grinding disc has been placed on the bearing plate.
In the embodiments described here, the clamping element is mounted on an end of a rocking lever (see
In the following an example of a method for the removal of a grinding disc from a grinding machine mounted on a manipulator will be summarized with reference to the flow chart shown in
Following this, the clamping element can once again be raised in order to release the clamped grinding disc. In the process it may happen, as described earlier, that the grinding disc remains adhered to the clamping element, which is undesirable, as it hampers the further transport of the grinding disc. In such cases, the grinding disc can be released using one or more pins (see
Terms such as “first”, “second”, and the like, are used to describe various elements, regions, sections, etc. and are also not intended to be limiting. Like terms refer to like elements throughout the description.
As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.
It is to be understood that the features of the various embodiments described herein may be combined with each other, unless specifically noted otherwise.
Although various embodiments have been illustrated and described with respect to one or more specific implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. With particular regard to the various functions performed by the above described components or structures (units, assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond—unless otherwise indicated—to any component or structure that performs the specified function of the described component (e.g., that is functionally equivalent), even if it is not structurally equivalent to the disclosed structure that performs the function in the herein illustrated exemplary implementations of the invention.
It will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2019 119 152.1 | Jul 2019 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/067693 | 6/24/2020 | WO |
