Machining unit and method for machining a component

Abstract

Disclosed is a machining unit for machining a bearing component. The machining unit includes an industrial robot and at least one abrasive tool. The at least one abrasive tool is coupled to the industrial robot and a controller. The controller is configured to control a movement path of the at least one abrasive tool such that a contact of the abrasive tool is in the normal direction to a surface of the component.

Claims

1. A machining unit for machining a bearing component, comprising: an industrial robot, at least one abrasive tool, wherein the at least one abrasive tool is coupled to the industrial robot, a controller in communication with the industrial robot and configured to control the industrial robot, wherein the industrial robot is configured to move the at least one abrasive tool through rotational motions, and wherein the controller is configured to control a rotational speed and/or a rotation direction imparted to the at least one abrasive tool by the industrial robot, a holder configured to hold the component, wherein the holder is configured to rotate the component, and the controller is in communication with the holder and is configured to control a rotational speed of the component via the holder, the controller is configured to control the industrial robot such that a movement path(S) of the at least one abrasive tool such that a contact between the abrasive tool and a surface of the component is in a normal direction relative to the surface, wherein the controller is configured to control the rotational speed of the component and the rotational speed of the at least one abrasive tool such that a ratio of the rotational speed of the at least one abrasive tool to the rotational speed of the component is unequal to an integer or a half integer.

2. The machining unit according to claim 1, wherein the machining unit further comprises a load sensor that is configured to measure a load applied to the component by the at least one the abrasive tool.

3. The machining unit according to claim 2, wherein the controller is configured to control the motion of the industrial robot, and the at least one abrasive tool based on the measured load, such that a force applied to the component by the at least one abrasive tool is constant.

4. The machining unit according to claim 1, wherein the controller is configured to determine when the machining is finished based on a calculated finishing time tf of the at least one abrasive tool and/or a measured amount of removed material, the controller using the following formulas to determine the calculated finishing time: tf=V/MMR and MRR=Q*wa, wherein tf is the calculated finishing time and wa is the axial contact width of the at least one abrasive tool and Q is the specific material removal rate capacity of the at least one abrasive tool, and wherein V is the volume to be removed.

5. The machining unit according to claim 1, wherein the machining unit further comprises a tool interface that is configured to couple the at least one abrasive tool to the industrial robot.

6. The machining unit according to claim 1, wherein the at least one abrasive tool is an abrasive stone or an abrasive belt.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, preferred embodiments of the invention are described in relation to the drawings, wherein the drawings are exemplarily only, and are not intended to limit the scope of protection. The scope of protection is defined by the accompanied claims, only.

(2) The figures show:

(3) FIG. 1: a schematic view of a machining unit according to an embodiment,

(4) FIG. 2: a schematic diagram shown a detail of the machining unit of FIG. 1, and

(5) FIG. 3: a schematic view of a holder according to another embodiment.

(6) In the following same or similar functioning elements are indicated with the same reference numerals.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 shows a schematic view of a machining unit 1 for machining a bearing component 2, such as a bearing ring as shown in FIG. 1. The component may be a bearing component, for example a bearing ring having a diameter larger than 400 mm as shown in FIG. 1. The machining unit 1 includes an industrial robot 4, which is equipped with an abrasive tool 6 having an abrasive belt 8. However, the abrasive tool 6 may not be limited to an abrasive belt 8 and may alternatively be an abrasive stone. An abrasive belt 8 is a belt made form a carrier material on which an abrasive material, such as aluminum oxide (Al.sub.2O.sub.3), silicon carbide (SiC) or cubic boron nitride (CBN) is provided. During operation, the abrasive belt 8 rotates. The abrasive tool 6 is coupled to the industrial robot 4 via a tool interface 10.

(8) The component 2 is held by a holder 14. The holder 14 rotates around a rotation axis 16, which also causes the component 2 to rotate. To remove material from a surface 18 of the component 2, the abrasive tool 6 is moved over the surface 18 of the component by the industrial robot 4. These movement of the industrial robot 4 are controlled by a controller 12 of the machining 1. In particular, the controller 12 is configured to control the industrial robot 4 to cause a movement path S (FIG. 2) of the abrasive tool 6 such that a contact of the abrasive tool 6 is in the normal direction to the surface 18 of the component 2. That is, the controller 12 sends control signal to the industrial robot 4 which causes the industrial robot 4 to move the abrasive tool 6. For example, the control signals may be sent via wire, such as a LAN connection, or wireless, particularly WLAN. Moreover, the controller 12 is also configured to control the rotational speed and rotation direction of the abrasive belt 8 as well as the rotational speed of the holder 14 and consequently the component 2. More particularly, the machining unit 1 allows to reduce the form deviation of the bearing ring to be less than 15 m, and the arithmetic average surface roughness Ra of the machined surface is less than 0.5 m.

(9) Moreover, the machining unit 1 comprises a load sensor 20 that measures a load applied to the component 2 by the abrasive tool 6. The load sensor 20 is arranged at the tool interface and measures the applied load in three independent axes. Preferably, the load is measured continuously. From these measured load values, the load applied in the normal direction of the component surface 18 is calculated based on the surface geometry of the component 2. Furthermore, the measured load is feedback to the controller 12 such that the controller 12 can control the motion of the industrial robot 4, and the abrasive tool 6 based on the measured load.

(10) For example, the controller 12 may control the industrial robot 4 and the abrasive tool 6 such that the force applied to the component 2 by the abrasive tool 6 is constant. Therefore, the controller 12 is configured to compare the measured load with a reference load stored in a storage device 22 in the controller 12 and adapt the applied load such that a difference between the measured load and the reference load is smaller than a predefined threshold value. The reference load may be experimentally predetermined, and the threshold value may be 1% of the reference load. This allows to reduce the produced form deviation and the arithmetic average surface roughness Ra of the machined surface.

(11) As mentioned above, the controller 12 is configured to control the rotation speed of the component 4 and the rotational speed of the abrasive band 8. Similar to the applied load, the controller 12 is also configured to compare the rotational speed of the belt 8 and the rotational speed of the component 2 to stored target values and adapt the respective command values such that an error in the rotational speed of the abrasive belt 8 is for example less than 0.5% of the target value, and/or such that an error in the rotational speed of the component 2 is for example less than 0.5% of the target value. Also, the controller 12 is configured to set the rotational speed of the component 4 and the rotational speed of the abrasive band 8 in such a way the ratio of the rotational speed of the abrasive belt 8 to the rotational speed of the component 2 is unequal to an integer or a half integer. Resulting in a produced form deviation that may be between 0 m and 15 m depending on the surface to be machined, and an arithmetic average surface roughness Ra of the machined surface that may be between 0.05 m and 0.5 m depending on surface to be machined.

(12) Furthermore, the tool interface 10 can also accommodate a second abrasive tool (not shown) such that the tool interface 10 can automatically change the used abrasive tool based on a command of the controller 12.

(13) In order to provide a more efficient machining of the component 2, the controller 12 is configured to determine when the machining is finished based on a calculated finishing time t.sub.f of the abrasive tool 6, wherein t.sub.f is calculated as the quotient of the volume to be removed V and a material removal rate MRR, t.sub.f=V/MMR, wherein the material removal rate MRR is calculated as product of the specific material removal rate capacity Q and the axial contact width of the at least one abrasive tool w.sub.a, MRR=Q*w.sub.a, and wherein V is the volume to be removed. For a rotational symmetric bearing component 2, V is determined by the formula:
V=.sub.S(x).sup.S(x).sub.A.sup.B2S(x)x.
This calculation principle is illustrated in FIG. 2. S(x) is the parameterized movement path S on the surface 18 of the component, is the material width to be removed, and A and B are the start point and end point of the movement path. The material to be removed is denoted with the reference numeral 24. The material removal rate MRR, the specific material removal rate capacity Q and the axial contact width of the at least one abrasive tool w.sub.a are stored in the storage device 22 of the controller 12 as well. Also, the controller 12 may also be configured to determine the volume V to be removed. Alternatively, or additionally, the removed material can be measured, and the finishing time can be determined based on the measured amount of the removed material. Determining the volume of the material to be removed allows for more efficient machining process and a bearing component 2 that has an improved surface roughness. Moreover, it also allows to minimize the produced form deviation.

(14) More particularly, the produced form deviation may be less than 15 m, preferably between 0 m and 15 m depending on the surface to be machined, and the arithmetic average surface roughness Ra of the machined surface may be of less than 0.5 m, preferably between 0.05 m and 0.5 m depending on the surface to be machined.

(15) FIG. 3 shows another embodiment of the holder 14. The holder 14 of FIG. 3 is configured to directly rotate the component 2, which is a rolling element in FIG. 3. Rotating the component 2 instead of the holder 14 is for example favorable for smaller components such as rolling elements or smaller bearing rings.

(16) In summary controlling the movement path of the abrasive tool 6 such that the contact of the abrasive tool 6 is in the normal direction to the surface geometry of the component has the advantage that the abrasive tool 6 is always in a defined orientation to the surface of the component 2 which avoids that the abrasive tool 6 removes more or less material depending on the contact angle between the abrasive tool and the surface.