Device and method for measuring the abrasiveness of an object

Abstract

The present invention relates to a device (100) for measuring the abrasiveness of an object. The device (100) comprises a contact surface (102) for contacting a surface of the object, a first electrical contact element (103) and a second electrical contact element (104) exposed at the contact surface (102), and means for detecting short circuits between the first electrical contact element (103) and the second electrical contact element (104), the abrasiveness of the object being related to the number and / or duration of the detected short circuits. The present invention also relates to a method for measuring the abrasiveness of an object.

Description

[0001] Device and method for measuring the abrasiveness of an object

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to a device and a method for measuring the abrasiveness of an object according to the preambles of the appended independent claims.

[0004] BACKGROUND OF THE INVENTION

[0005] In many applications, an object that is used for polishing, sanding, grinding or cutting a surface of a workpiece is required to have a defined and constant abrasiveness to achieve a desired result. Typically, however, the abrasiveness of the object changes during the polishing, sanding, grinding and cutting processes, which, unless it is taken care of, will result in the deterioration of the surface of the workpiece. Thus, there is a great need for the abrasiveness measurements in these processes.

[0006] Various devices have been developed for the measurement of the abrasiveness of an object. Most of the known devices are based on measuring the abrasion resistance by moving a test piece across a surface of the object and calculating the force that is required to move the test piece across the surface.

[0007] A problem associated with the known devices is that they are difficult to use. Another problem associated with the known devices is that they are, in many cases, not accurate enough. Yet another problem associated with the known devices is that they cannot be used while a workpiece is being polished, sanded, ground or cut with an object.

[0008] OBJECTIVES OF THE INVENTION

[0009] It is the main objective of the present invention to reduce or even eliminate the prior art problems presented above.

[0010] It is an objective of the present invention to provide a device and a method for measuring the abrasiveness of an object. It is also an objective of the invention to provide a device and a method for tribological measurements enabling to measure the abrasiveness of an object easily and accurately. It is yet a further objective of the invention to provide a device and a method that can be applied in various polishing, sanding, grinding and cutting applications to measure the abrasiveness of an object. It is yet a further objective of the invention to provide a device and a method enabling to measure the abrasiveness of an object while the object is being used for polishing, sanding, grinding or cutting a workpiece.

[0011] In order to realise the above-mentioned objectives, the device and the method according to the invention are characterised by what is presented in the characterising portions of the appended independent claims. Advantageous embodiments of the invention are described in the dependent claims.

[0012] DESCRIPTION OF THE INVENTION

[0013] A device according to the invention for measuring the abrasiveness of an object comprises a contact surface for contacting a surface of the object, a first electrical contact element and a second electrical contact element exposed at the contact surface, and means for detecting short circuits between the first electrical contact element and the second electrical contact element, the abrasiveness of the object being related to the number and / or duration of the detected short circuits.

[0014] A method according to the invention for measuring the abrasiveness of an object comprises arranging a contact surface of a device according to the invention in contact with a surface of the object, moving the device and the object relative to each other while keeping the contact surface in contact with the surface of the object, and detecting short circuits between the first electrical contact element and the second electrical contact element, the abrasiveness of the object being related to the number and / or duration of the detected short circuits.

[0015] The device and the method according to the invention enable to measure the abrasiveness of an object. The object is preferably an abrasive object, such as a coated abrasive, a bonded abrasive or a free abrasive, that is used for polishing, sanding, grinding or cutting a workpiece. The object can be, for example, a polishing or lapping pad, an abrasive paper, a grinding disc, or a cutting wheel. The device and the method according to the invention are suitable for measuring the abrasiveness of an object that has a surface made of an electrically non-conductive material.

[0016] In the present invention, the abrasiveness of an object is measured by moving the contact surface along the surface of the object and detecting short circuits between the first electrical contact element and the second electrical contact element. The abrasiveness of the object is determined based on the detected short circuits. The contact surface can be moved along the surface of the object by moving the device with respect to the object and / or by moving the object with respect to the device. A short circuit may occur when an electrically conductive particle (material) on the surface of the object connects the electrical contact elements. The duration of the short circuit depends on the size of the electrically conductive particle. The electrically conductive particle can be a particle originating from one of the electrical contact elements or from a workpiece due to abrasion between the object and the electrical contact element or the workpiece. The electrically conductive particle can also be a particle originating from a separate wearing part, preferably made of a ductile material, due to abrasion between the object and the wearing part. The electrically conductive particle can also be an abrasive particle contained in a polishing suspension that is dispensed on the surface of the object. The electrically conductive particle may also be any unwanted particle that can originate from various sources. A short circuit may also occur due to smearing of one or both electrical contact elements, i.e., due to the displacement of electrical contact element material on the contact surface. The detection of short circuits can be based on the monitoring of voltage or current changes in an electrical circuit that comprises the first electrical contact element and the second electrical contact element.

[0017] The contact surface of the device is meant to be in contact with a surface of an object when the abrasiveness is measured. The contact surface is preferably planar since in most cases the surface of the object is planar. Preferably, the contact surface is circular. In multidirectional abrasion, for example in polishing, the contact surface is preferably circular, and it can rotate freely, and it can have a diameter of 10-200 mm or 20-100 mm.

[0018] The first electrical contact element and the second electrical contact element are arranged in the device so that they are exposed at the contact surface. This means that the first electrical contact element and the second electrical contact element can be in contact with the surface of the object when the contact surface is arranged in contact with the surface of the object. The first electrical contact element and the second electrical contact element are electrically isolated from each other with an electrically insulating element. The first electrical contact element and the second electrical contact element are made of an electrically conductive material.

[0019] The abrasiveness of the object is related to the number and / or duration of the detected short circuits. The larger the number of the detected short circuits per time interval and / or the longer the duration of the detected short circuits, the more abrasive the object. From the short circuit data, various indicators can be calculated for the evaluation and interpretation of the abrasiveness of the object. These are, for example, the number of short circuits per time interval, the average duration of short circuits, and the distribution of time intervals between short circuits. The device may comprise means for determining the abrasiveness of the object based on the detected short circuits. The determining means may be configured to calculate, for example, the number of short circuits per time interval, the average duration of short circuits, and the distribution of time intervals between short circuits. The determining means may comprise a processor and a memory including computer program code, the memory and the computer program code being configured to, with the processor, calculate these indicators. The determining means can also be integrated, for example, implemented as embedded IC, or using distributed computing, parallel computing, or edge computing.

[0020] An advantage of the device and the method according to the invention is that they enable to measure the abrasiveness of an object easily and accurately. Another advantage of the device and the method according to the invention is that they can be applied in various polishing, sanding, grinding and cutting applications to measure the abrasiveness of an object. Yet another advantage of the device and the method according to the invention is that they enable to measure the abrasiveness of an object while the object is being used for polishing, sanding, grinding or cutting a workpiece.

[0021] According to an embodiment of the invention the means for detecting short circuits between the first electrical contact element and the second electrical contact element comprises a resistor having a first terminal and a second terminal, the first terminal being electrically connected to the first electrical contact element, a DC voltage source configured to apply a DC voltage between the second electrical contact element and the second terminal of the resistor, and means for measuring the voltage at a node between the resistor and the first electrical contact element, or the voltage across the resistor, or the current through the resistor.

[0022] The electrical resistance of the resistor can be, for example, 100 Q-10 kQ, 200 Q- 5 kQ, or 500 Q-2 kQ. The voltage of the DC voltage source can be, for example, 1 - 5 V, 0.5-2 V, or 2-10 V.

[0023] According to an embodiment of the invention the first electrical contact element is made of a ductile material. In this text, by a ductile material is meant a material having an elongation at break of more than 1 %. Elongation at break is the ratio between changed length and initial length after breakage of a material. An advantage of having the first electrical contact element made of a ductile material is that it can easily deform due to abrasion. According to an embodiment of the invention the second electrical contact element is made of a ductile material.

[0024] According to an embodiment of the invention the ductile material is selected from a group consisting of metals, alloys, polymers, copolymers, and organic semiconductors. The ductile material can be, for example, aluminium, titanium, gold, copper, aluminium alloy (e.g. 3003 aluminium alloy), steel, stainless steel (e.g. 304 stainless steel), or brass (e.g. 230 brass).

[0025] According to an embodiment of the invention the second electrical contact element is made of a non-ductile material. In this text, by a non-ductile material is meant a material having an elongation at break of less than 1 %.

[0026] According to an embodiment of the invention the non-ductile material is selected from a group consisting of metals, alloys, polymers, copolymers, and inorganic semiconductors.

[0027] According to an embodiment of the invention the first electrical contact element has a shape of a cylinder, and the second electrical contact element has a shape of a hollow cylinder, wherein the first electrical contact element is arranged concentrically inside the second electrical contact element. Preferably, in this case, the first electrical contact element is made of a ductile material.

[0028] The diameter of the first electrical contact element can be, for example, less than 1 mm, 1 -50 mm, or 50-80 mm. The gap between the first electrical contact element and the second electrical contact element is preferably less than 2 mm, and more preferably less than 50 pm. The wall thickness of the second electrical contact element can be, for example, 0.1 -10 mm or 1-5 mm.

[0029] According to an embodiment of the invention the device comprises an electrically insulating element having a shape of a hollow cylinder, wherein the electrically insulating element is arranged concentrically between the first electrical contact element and the second electrical contact element.

[0030] Preferably, the inner diameter of the electrically insulating element is essentially the same as the diameter of the first electrical contact element, and the outer diameter of the electrically insulating element is essentially the same as the inner diameter of the second electrical contact element. The electrically insulating element can, for example, be made of a polymer, for example epoxy or acrylate polymer, or a resin impregnated paper. According to an embodiment of the invention a minimum distance between the first electrical contact element and the second electrical contact element is less than 2 mm. The minimum distance between the first electrical contact element and the second electrical contact element is preferably less than 200 pm and more preferably less than 50 pm.

[0031] According to an embodiment of the invention the device comprises means for transmitting the detected short circuits to a computer device via a wireless communication network.

[0032] According to an embodiment of the invention the device comprises a cylindrical housing having the contact surface at one of its ends. The housing can, for example, be made of a metal alloy, a polymer or a composite material. The diameter of the housing can be, for example, 10-100 mm, 10-50 mm, or 50-100 mm. The height of the housing can be, for example, 10-100 mm, 10-50 mm, or 50-100 mm.

[0033] According to an embodiment of the invention the step of detecting short circuits between the first electrical contact element and the second electrical contact element comprises applying a DC voltage between the second electrical contact element and a second terminal of a resistor, a first terminal of the resistor being electrically connected to the first electrical contact element, and measuring the voltage at a node between the resistor and the first electrical contact element, or the voltage across the resistor, or the current through the resistor.

[0034] According to an embodiment of the invention the measured voltage at a node between the resistor and the first electrical contact element is processed using an analog and / or digital electrical circuit to produce one or more output values corresponding to one or more characteristics of the measured voltage signal.

[0035] According to an embodiment of the invention the step of measuring the voltage at a node between the resistor and the first electrical contact element comprises using an integrating analog circuit to produce a voltage output corresponding to a pulse frequency.

[0036] The present invention also relates to use of a device according to the invention for measuring the abrasiveness of an object.

[0037] The exemplary embodiments of the invention presented in this text are not interpreted to pose limitations to the applicability of the appended claims. The verb “to comprise” is used in this text as an open limitation that does not exclude the existence of also unrecited features. The features recited in the dependent claims are mutually freely combinable unless otherwise explicitly stated.

[0038] The exemplary embodiments presented in this text and their advantages relate by applicable parts to the device as well as the method according to the invention, even though this is not always separately mentioned.

[0039] BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Fig. 1 illustrates a perspective view of a device according to an embodiment of the invention, fig. 2 illustrates a schematic cross-sectional view of a device of fig. 1 , and fig. 3 illustrates the use of a device of fig. 1.

[0041] DETAILED DESCRIPTION OF THE DRAWINGS

[0042] Fig. 1 illustrates a perspective view of a device according to an embodiment of the invention. The device 100 can be used for measuring the abrasiveness of an object (not shown in fig. 1 ).

[0043] The device 100 comprises a cylindrical housing 101 having a contact surface 102 at one of its ends. The contact surface 102 is meant to be in contact with a surface of the object when the abrasiveness is measured.

[0044] The device 100 comprises electrical contact elements 103 and 104, which are exposed at the contact surface 102. The electrical contact element 103 is arranged concentrically inside the electrical contact element 104. An electrically insulating element 105 is arranged concentrically between the electrical contact elements 103 and 104.

[0045] The device 100 comprises means for detecting short circuits that occur between the electrical contact elements 103 and 104 when the contact surface 102 moves along the surface of the object. The means for detecting short circuits are shown in fig. 2 and explained next.

[0046] Fig. 2 illustrates a schematic cross-sectional view of a device of fig. 1 . The means for detecting short circuits between the electrical contact elements 103 and 104 comprises a resistor 106 and a DC voltage source 107, which are electrically connected in series between the electrical contact elements 103 and 104. The means for detecting short circuits between the electrical contact elements 103 and 104 also comprises means 108 for measuring the voltage across the resistor 106. A short circuit that occurs between the electrical contact elements 103 and 104 produces a rapid increase in the measured voltage; the voltage increases from zero to a value that is dependent on the applied DC voltage.

[0047] The device 100 comprises a transceiver 109 that is connected to the means 108 for measuring the voltage across the resistor 106. The transceiver is used for transmitting the short circuit data to a computer device (not shown in fig. 2) via a wireless communication network.

[0048] Fig. 3 illustrates the use of a device of fig. 1. In fig. 3, the device 100 is used for measuring the abrasiveness of a polishing pad 110. On a surface of the polishing pad 110, there are a plurality of electrically conductive particles 111. The electrically conductive particles 111 have been detached from the electrical contact elements 103 and 104 due to abrasion.

[0049] The device 100 is arranged on the polishing pad 110 in such a manner that the contact surface 102 is in contact with the surface of the polishing pad 110. During the measurement, the device 100 is moved on the polishing pad 110 in a direction that is shown by an arrow A.

[0050] As the contact surface 102 moves along the surface of the polishing pad 110, it encounters the electrically conductive particles 111 . A short circuit occurs every time one of the electrically conductive particles 111 connects the electrical contact elements 103 and 104. The duration of the short circuit depends on the size of the electrically conductive particle 111. The electrical contact elements 103 and 104 are shown in fig. 3 with dashed lines.

[0051] Only advantageous exemplary embodiments of the invention are described in the figures. It is clear to a person skilled in the art that the invention is not restricted only to the examples presented above, but the invention may vary within the limits of the claims presented hereafter. Some possible embodiments of the invention are described in the dependent claims, and they are not to be considered to restrict the scope of protection of the invention as such.

Claims

Claims1 . A device for measuring the abrasiveness of an object, characterised in that the device comprises:- a contact surface for contacting a surface of the object,- a first electrical contact element and a second electrical contact element exposed at the contact surface, and- means for detecting short circuits between the first electrical contact element and the second electrical contact element, the abrasiveness of the object being related to the number and / or duration of the detected short circuits.

2. The device according to claim 1 , characterised in that the means for detecting short circuits between the first electrical contact element and the second electrical contact element comprises:- a resistor having a first terminal and a second terminal, the first terminal being electrically connected to the first electrical contact element,- a DC voltage source configured to apply a DC voltage between the second electrical contact element and the second terminal of the resistor, and- means for measuring the voltage at a node between the resistor and the first electrical contact element, or the voltage across the resistor, or the current through the resistor.

3. The device according to claim 1 or 2, characterised in that the first electrical contact element is made of a ductile material.

4. The device according to any of the preceding claims, characterised in that the second electrical contact element is made of a ductile material.

5. The device according to claim 3 or 4, characterised in that the ductile material is selected from a group consisting of metals, alloys, polymers, copolymers, and organic semiconductors.

6. The device according to any of claims 1 to 3, characterised in that the second electrical contact element is made of a non-ductile material.

7. The device according to claim 6, characterised in that the non-ductile material is selected from a group consisting of metals, alloys, polymers, copolymers, and inorganic semiconductors.

8. The device according to any of the preceding claims, characterised in that the first electrical contact element has a shape of a cylinder, and the second electrical contact element has a shape of a hollow cylinder, wherein the first electrical contact element is arranged concentrically inside the second electrical contact element.

9. The device according to claim 8, characterised in that the device comprises an electrically insulating element having a shape of a hollow cylinder, wherein the electrically insulating element is arranged concentrically between the first electrical contact element and the second electrical contact element.

10. The device according to claim 8 or 9, characterised in that a minimum distance between the first electrical contact element and the second electrical contact element is less than 2 mm.11 . The device according to any of the preceding claims, characterised in that the device comprises means for transmitting the detected short circuits to a computer device via a wireless communication network.

12. The device according to any of the preceding claims, characterised in that the device comprises a cylindrical housing having the contact surface at one of its ends.

13. A method for measuring the abrasiveness of an object, characterised in that the method comprises:- arranging a contact surface of a device according to any of the preceding claims in contact with a surface of the object,- moving the device and the object relative to each other while keeping the contact surface in contact with the surface of the object, and- detecting short circuits between the first electrical contact element and the second electrical contact element, the abrasiveness of the object being related to the number and / or duration of the detected short circuits.

14. The method according to claim 13, characterised in that the step of detecting short circuits between the first electrical contact element and the second electrical contact element comprises:- applying a DC voltage between the second electrical contact element and a second terminal of a resistor, a first terminal of the resistor being electrically connected to the first electrical contact element, and- measuring the voltage at a node between the resistor and the first electrical contact element, or the voltage across the resistor, or the current through the resistor.

15. Use of a device according to any of claims 1 to 12 for measuring the abrasiveness of an object.