Abrasive Disk, Hand-Held Power Tool and Control Method

Abstract

An abrasive disk has one or more layers in which abrasive grains are embedded. Embedded in one layer is a sensor for detecting an original periphery of the abrasive disk that has been altered by wear. The sensor has at least one closed conductor loop which is arranged at a radial distance from the original periphery such that, when the original periphery is worn by more than the radial distance, the conductor loop is interrupted. A transponder emits a radio signal indicative of whether the conductor loop is closed or interrupted.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of PCT International Application No. PCT/EP2018/079648, filed Oct. 30, 2018, which claims priority under 35 U.S.C. § 119 from European Patent Application No. 17201070.4, filed Nov. 10, 2017, the entire disclosures of which are herein expressly incorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a disk, a hand-held power tool for abrasive disks and a control method.

Abrasive disks rotate at high speed. During use of the disk, abraded matter of the disk and of the machined material fly away from the disk at high speed. Furthermore, the disk is subject to high loads due to centrifugal force. For safety reasons, therefore, the regulatory authorities set an upper limit for the rotational speed.

Abrasive disks are subject to wear. The wear leads to a reduced periphery and thus reduced rotational speed. The reduced rotational speed adversely affects the machining performance of the disks.

An abrasive disk according to the invention has one or more layers, in which abrasive grains are embedded. Embedded in one layer is sensor for detecting an original periphery of the abrasive disk that has been altered by wear. The sensor has at least one closed conductor loop, which is arranged at a radial distance from the original periphery such that, when the original periphery is worn by more than the radial distance, the conductor loop is interrupted. A transponder emits a radio signal indicative of whether the conductor loop is closed or interrupted.

The radio signals indicate the radial wear of the disk. A hand-held power tool can adjust the speed accordingly.

A hand-held power tool for the abrasive disk has a holder for the abrasive disk, an electric motor for rotating the abrasive disk and a speed control for the electric motor. A communication device is set up to receive the radio signal emitted by the transponder of the abrasive disk. A device controller sets the speed for the speed control based on the radio signal received.

The following description explains the invention on the basis of exemplary embodiments and Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an electric angle grinder;

FIG. 2 shows an abrasive disk in cross section;

FIG. 3 shows the abrasive disk in a plan view;

FIG. 4 shows a detail of an abrasive disk; and

FIG. 5 shows a detail of an abrasive disk.

DETAILED DESCRIPTION OF THE DRAWINGS

identical or functionally identical elements are indicated by the same reference numerals in the Figures, unless stated otherwise.

FIG. 1 shows an electric hand-held power tool 1 for abrasive disks 2. The hand-held power tool 1 has a tool holder 3 for an abrasive disk. 2 The tool holder 3 is coupled to an electric motor 4, which rotatably drives the tool holder 3 about its axis. A speed control 5 controls the electric motor 4. The speed control 5 limits the speed to a maximum speed in order to prevent damage to the abrasive disk 2 and possible injury to the user. A protective hood 6 annularly encloses more than half of the tool holder 3, in order to protect the user from flying sparks and substance abrasively removed. The hand-held power tool 1 has a handle 7 with which the user can hold and guide the hand-held power tool 1 in operation. At or near the handle 7, a button 8 for starting the electric motor 4 is arranged. The hand-held power tool 1 can be powered from the grid or by means of batteries 9.

The hand-held power tool 1 has a device controller 10. Among other things, the device controller 10 sets the target speed for the speed control 5. The device controller 10 may access a memory 11, in which a target speed is stored. The device controller 10 may also access a communication device 12 in order to communicate with an abrasive disk 2. The communication device 12 has a transmitter 13 for transmitting radio-based signals and a receiver 14 for receiving a radio-based response of the abrasive disk 2. A transmission power of the transmitter 13 is preferably sufficient to power a transponder, e.g., a radio-frequency identification (RFID) chip, without its own energy source via the transmission power.

When the button 8 is actuated, the device controller 10 directs a request to the disk 2 to identify it. The disk 2, if equipped with a transponder 15, reports an identification number or type number. The device controller 10 checks whether the type number differs from the disk 2 last used. If this is the case, the device controller 10 inquires what is a maximum permissible speed for the disk 2. The device controller 10 stores the maximum permissible speed in the memory 11. Preferably, the disk 2 transmits a list of different maximum speeds to be used depending on a degree of wear of the disk 2. The degree of wear is coded in radio signals which are transmitted in the list. The device controller 10 stores the list in the memory 11. The device controller 10 sets the speed of the speed control 5 to the maximum permissible speed that corresponds to the current degree of wear. The device controller inquires at intervals via the communication device 12 what is the degree of wear of the disk 2. The radio signal received as a response by the communication device 12 is compared with the stored list. The maximum permissible speed associated with the radio signal is transmitted to the speed control 5.

FIG. 2 schematically shows an embodiment of an abrasive disk 2 in cross section. The abrasive disk 2 shown is a multi-layer cutting disk with different grains. The abrasive disk 2 has a middle layer 16 with first grains. The middle layer 16 can be produced for example by an electrodeposited matrix in which the grains are distributed. The two outer layers 17, 18 can also be produced with an electrodeposited matrix and scattered embedded grains. The grains of the middle layer 16 may be larger than the grains of the outer layers 17, 18. The grains given by way of example have a diameter of 4 μm to 10 μm and 10 μm to 20 μm, respectively. The production of the layers 18 is purely exemplary. Another method given by way of example is based on fabrics that are impregnated with resins mixed the grains. The resins are then cured. The number of different layers is also purely exemplary. Other disks have one, two or more different abrasive layers. Typically, the disks 2 are provided with a cover layer 19, on which the disk type, manufacturer, etc. are indicated.

The disks are produced with different diameters. Diameters given by way of example are 8.9 cm and 11.2 cm. FIG. 3 illustrates an instance of wear given by way of example. The as-new disk 2 has the original periphery 20. The disks 2 become worn during use, which reduces the diameter and periphery. Examples of a periphery 21 of a worn disk 2 are shown by dashed lines. In the following, the original diameter, original radius or original periphery 20 designates the respective property of a new, unused abrasive disk 2.

Embedded in the abrasive disk 2 is a sensor 22, which detects wear and the degree of wear of the disk 2. The sensor 22 is based on one or more closed conductor loops 23, 24. The conductor loops 23, 24 run parallel to the abrasive layers 16. For example, the conductor loop 23 may be printed on a film of non-conductive plastic. The film is stacked as a further layer 25 with the other layers 16. The film may be arranged as shown on the abrasive layers 16 or between the abrasive layers 18. The conductor loops 23, 24 have a low mechanical strength. The conductor loops 23, 24 preferably have a height of less than 100 μm. The conductor loops 23, 24 are preferably made of copper or graphite.

The closed conductor loop 23 has a (detection) portion 26 which is closest to the periphery 20 and farthest from a center of the disk 2. The detection portion 26 is at a radial distance 27. The detection portion 26 given by way of example lies within the original periphery 20 and outside a worn periphery 21. The radius of the worn periphery 20 corresponds to the original radius reduced by the distance 27. As the disk 2 becomes worn, the detection portion 26 is exposed by the distance 27, i.e., up to the worn periphery 21, and destroyed. The previously closed conductor loop 23 is then interrupted.

Preferably arranged on the disk 2 is a sensor 22, for example on in the layer 25 with the conductor loops. The sensor 22 may be realized for example as an RFID chip. The sensor 22 checks the closed or interrupted state of the conductor loop 23. The sensor 22 determines the electrical properties of the conductor loop 24, e.g., resistivity, inductance and electromagnetic resonant frequency. The sensor 22 is based for example on an ohmmeter for determining the electrical resistance value of the conductor loop 23. If the resistance value exceeds a threshold value, e.g., 1 megohm, the conductor loop 24 is considered to be interrupted, otherwise the conductor loop 23 is considered to be closed. The conductor loop 23 is galvanically connected to the sensor 22. The ohmmeter applies a voltage to the conductor loop 23 and measures the amplitude of the current flowing in the conductor loop 23. Another configuration of the sensor 22 determines the inductance of the conductor loop 23. A further configuration of the sensor 22 determines whether the resonant frequency of the conductor loop 23 changes. The conductor loop 23 may be part of an electrical oscillating circuit or be inductively coupled to an oscillating circuit of the sensor 22. While the conductor loop 23 or the oscillating circuit can be excited at a predetermined resonant frequency with a closed conductor loop 23, this is not possible with an interrupted conductor loop, or if it is at a different resonant frequency. The sensor 22 excites the oscillating circuit at the predetermined resonant frequency. If the power consumption exceeds a threshold value due to the resonant excitation, the conductor loop 23 is considered to be closed, otherwise it is considered to be interrupted. The described configurations for determining the electrical properties of the conductor loop 23 are given by way of example. The sensor 22 may also be passively formed. An external transmission source excites the oscillating circuit 28.

The sensor 22 includes a transponder 15. The transponder 15 may consist of a passive antenna. The transponder 15 transmits the state of the conductor loop, i.e., whether the conductor loop is interrupted or whether the conductor loop is closed.

In one configuration, the sensor 22 includes a memory 29, in which characteristics of the abrasive disk 2 are stored. For example, a maximum permissible speed for the disk 2 when the conductor loop 23 is closed and a maximum permissible speed for the disk 2 when the conductor loop 23 is interrupted are stored in the memory 29. The sensor 22 determines the currently permissible rotational speed based on the determined state of the conductor loop 23. The permissible speed is output via the transponder 15. In one configuration, the transponder 15 can transmit both values, i.e., for the closed conductor loop 23 and the interrupted conductor loop 23, at one time to the communication device 12 of the hand-held power tool 1. At the same time, the transponder 15 transmits the radio signals or their coding for the two states. An evaluation can thus be transmitted to the device controller 10.

In addition to the first conductor loop 23 described, the sensor 22 may have a. second conductor loop 24 or a number of conductor loops. The second conductor loop 24 is at a greater distance 30 from the original periphery 20. Accordingly, the second conductor loop 24 is only severed when there is a greater degree of wear 31. The second conductor loop 24 has a detection portion 32 in a way similar to the first conductor loop 23. The detection portion 32 is destroyed when the abrasive disk 2 is worn by more than the distance 30. The sensor 22 detects whether the second conductor loop 24 is closed or interrupted. The two conductor loops 23, 24 can be galvanically isolated as shown. The sensor 22 can scan the conductor loops 23, 24 one after the other. With the second conductor loop 24, three states of wear can be distinguished: low, medium, high. For each of the states of wear, a separate maximum speed can be defined, and for example stored in the memory 29. The transponder 15 transmits a radio signal in which the state of both conductor loops 23, 24 is coded, The number of conductor loops 23, 24 may be greater than two, e.g., up to ten conductor loops. The sensor 22 and the memory 29 need only be scaled accordingly.

FIG. 4 and FIG. 5 show other configurations of the conductor loops, in which the conductor loops 33, 34 are galvanically connected. A first conductor loop 33 is at the smallest distance 27 from the original periphery 20. A second conductor loop 24 is at a greater distance 30 from the original periphery 20. Their respective detection portions 35, 36 are radially offset from one another, as in the first embodiment.

The sensor 22 may for example determine the change in resistance of the connected conductor loops. The conductor loops 33, 34 form an electrical parallel circuit. With each interrupted conductor loop 33, the resistance value of the parallel circuit increases. The conductor loops 33, 34 preferably each have a clearly measurable resistance 37. The resistance 37 may for example be produced by using graphite instead of a metal for the conductor loops 33, 34.

The sensor 22 may determine the inductance or resonant frequency of the parallel-connected conductor loops 33, 34. The inductance of the parallel circuit decreases with each severed conductor loop 33. The resonant frequency increases with each separated conductor loop 33. The parallel-connected conductor loops 33, 34 may be part of an oscillating circuit 28 of the sensor 22 or be inductively excited via an oscillating circuit 28 of the sensor 22.

Claims

1.-14. (canceled)

15. An abrasive disk, comprising:

a first layer;

a sensor embedded in the first layer, wherein an original periphery of the abrasive disk is detectable by the sensor;

wherein the sensor has a first closed conductor loop which is disposed at a first radial distance from the original periphery such that when the original periphery is worn by more than the first radial distance the first closed conductor loop is interrupted; and

a transponder, wherein a radio signal is emittable by the transponder which is indicative of whether the first closed conductor loop is closed or interrupted.

16. The abrasive disk as claimed in claim 15, wherein the sensor has a second closed conductor loop which is disposed at a second radial distance from the original periphery that is greater than the first radial distance and wherein the radio signal is indicative of which one of the first closed conductor loop and the second closed conductor loop is interrupted.

17. The abrasive disk as claimed in claim 16, wherein the first closed conductor loop and the second closed conductor loop have a different radial extent.

18. The abrasive disk as claimed in claim 16, wherein the first closed conductor loop and the second closed conductor loop have a different length.

19. The abrasive disk as claimed in claim 16, wherein the first closed conductor loop and the second closed conductor loop have a different electromagnetic resonant frequency.

20. The abrasive disk as claimed in claim 16, wherein the first closed conductor loop, the second closed conductor loop, and the transponder are printed on a film.

21. The abrasive disk as claimed in claim 15, wherein the sensor has a memory integrated in the sensor in which a measure of a maximum permissible rotational speed of the abrasive disk is stored in dependence on the first closed conductor loop when severed and wherein the measure of the maximum permissible rotational speed is includable in the radio signal.

22. The abrasive disk as claimed in claim 15, wherein the sensor and the transponder are integrated in a radio-frequency identification (RFID) chip.

23. A hand-held power tool, comprising:

the abrasive disk as claimed in claim 15;

a holder, wherein the holder holds the abrasive disk;

an electric motor for rotating the abrasive disk;

a speed control for the electric motor;

a communication device, wherein a radio signal emitted by the transponder of the abrasive disk is receivable by the communication device; and

a device controller, wherein a speed for the speed control is settable based on a received radio signal.

24. The hand-held power tool as claimed in claim 23, wherein the device controller sets a nominal speed if the communication device does not receive a radio signal.

25. The hand-held power tool as claimed in claim 23 further comprising a memory in which a measure of a maximum permissible rotational speed of the abrasive disk is stored.

26. The hand-held power tool as claimed in claim 25, wherein the device controller reads out a list of maximum permissible rotational speeds of the abrasive disk stored in the memory.

27. A control method for the hand-held power tool as claimed in claim 23, comprising the steps of:

sending a first inquiry concerning a state of wear of the abrasive disk; and

adjusting a rotational speed of the abrasive disk based on a received radio signal.

28. The control method for the hand-held power tool as claimed in claim 27, further comprising the steps of:

sending a second inquiry concerning a maximum rotational speed of the abrasive disk which is indicative of a degree of wear of the abrasive disk and which is stored in a memory of the hand-held power tool; and

adjusting the rotational speed of the abrasive disk based on a response to the second inquiry.

29. The abrasive disk as claimed in claim 15 further comprising a second layer disposed adjacent to the first layer wherein abrasive grains are embedded in the second layer.

30. The abrasive disk as claimed in claim 15 wherein abrasive grains are embedded in the first layer.