Patent Application
20220395955
The present invention relates to a device and a method for polishing a specimen according to the preambles of the appended independent claims.
Various polishing devices are known in the prior art for polishing rock, metallographic and other specimens of solid materials for different applications. The polishing devices enable to polish specimens with minimal manual work.
An exemplary polishing device comprises a rotatable polishing platen and a polishing pad that is attached to the surface of the polishing platen. The polishing device also comprises a specimen holder for holding one or more specimens against the polishing pad. As the polishing platen is rotated, the polishing pad polishes the specimen(s).
A polishing suspension is typically used in the polishing device to enhance the polishing action and to prevent overheating during the polishing process. The polishing suspension contains water and/or other suitable liquids, such as ethanol or glycol for moistening, cooling and lubricating the polishing pad and abrasive particles, such as diamond, aluminium oxide or colloidal silica for polishing of the surface of the specimen. The polishing device may comprise a dispenser for dispensing the polishing suspension at a predefined rate on the polishing pad. The dispenser can, for example, be configured to dispense a certain amount of the polishing suspension at regular time intervals on the polishing pad.
A problem associated with the known polishing devices is that, during the polishing, the moisture in the polishing pad can vary considerably as a function of time and as a function of the position on the polishing pad. This has a negative effect on the polishing result. If the polishing pad is too wet, the friction between the specimen and the polishing pad is small, which makes the polishing ineffective and increases the polishing time. If, on the other hand, the polishing pad is too dry, there is a risk that the polishing of the specimen fails due to the large friction between the specimen and the polishing pad.
It is the main objective of the present invention to reduce or even eliminate the prior art problems presented above.
It is an objective of the present invention to provide a device and a method for polishing a specimen. In more detail, it is an objective of the invention to provide a device and a method enabling to provide and maintain a substantially constant and uniform moisture content in the polishing pad during the polishing process. It is a further objective of the invention to provide a device and a method enabling to polish a specimen with a uniform and high-quality polishing result.
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.
A device according to the invention for polishing a specimen comprises a polishing platen rotatable about an axis, a polishing pad attached to the polishing platen, a specimen holder for holding the specimen against the polishing pad, means for measuring a physical quantity in a plurality of positions on the polishing pad, the physical quantity being indicative of the moisture or the friction, and means for dispensing a polishing suspension, based on values of the measured physical quantity, to the plurality of positions on the polishing pad.
The device according to the invention, i.e. the polishing device, can be used to polish a specimen (i.e. an object) of a solid material, such as a piece of a natural (e.g. rock, mineral, ore or meteorite) or artificial (e.g. metal, concrete, ceramic, composite or semiconductor) material. In this text, the term polishing means polishing, fine-grinding and grinding processes with a polishing pad and a polishing suspension.
The specimen to be polished is held against the surface of the polishing pad with the specimen holder. The specimen holder can be configured to hold one or more specimens against the polishing pad. The number of specimens that can be held with the specimen holder against the polishing pad can be, for example, 1, 2-5, 6-10, or more than 10. The specimen holder can comprise, for example, one or more inserts in which the specimens can move freely or are secured by clamping. The specimen holder can be attached to a polishing head that presses the specimen(s) with an adjustable pressing force against the polishing pad. The pressing force can be adjusted, for example, based on the values of the measured physical quantity.
The polishing pad can be made of different materials, such as a fibrous cloth (e.g. real silk, polyester or acetate) or synthetic non-fibrous (e.g. neoprene, polyurethane or composite) material. The polishing pad is preferably disc-shaped, i.e. it has a flat circular shape. The polishing pad is preferably porous, enabling it to absorb the polishing suspension. The diameter of the polishing pad can be, for example, less than 500 mm, preferably 200-400 mm. The thickness of the polishing pad can be, for example, less than 3 mm, preferably less than 2 mm, and more preferably less than 1 mm.
The polishing pad is attached, preferably releasably, to the surface of the rotatable polishing platen. As the polishing platen is rotated, the polishing pad polishes the specimen. The polishing platen can be made of a heat conductive and corrosion resistant material, such as aluminium, bronze or stainless steel, or of a plastic, polymer or composite material. The polishing platen may comprise an electrically insulated electrical contact element (for example a sheet made of austenitic stainless steel and having a thickness of about 0.5 mm) on its surface, to which an electrical contact element (for example a carbon brush) of a measuring instrument can be electrically connected. The polishing platen is preferably disc-shaped and heat conductive. The diameter of the polishing platen can be, for example, less than 500 mm, preferably 200-400 mm. Preferably, the diameters of the polishing platen and the polishing pad are essentially the same. The thickness of the polishing platen can be, for example, 20-50 mm. The optimal thickness of the polishing platen depends on the diameter and the material of the polishing platen.
The polishing device may comprise an actuator, such as an electric motor, for rotating the polishing platen. The actuator can be configured to rotate the polishing platen, for example, at a rotational speed of 0-600 rpm. The actuator can be configured to adjust the rotational speed of the polishing platen based on the values of the measured physical quantity. For example, in a case where the friction exceeds a predetermined threshold value or the moisture falls below a predetermined threshold value, the actuator can be configured to reduce the rotational speed of the polishing platen. To reduce possible interferences caused by the actuator, it may be beneficial to add an electrical insulation layer between the polishing platen and the actuator.
In addition to the polishing platen, also the specimen holder can be rotatable. The specimen holder can be rotatable about an axis, which is parallel to the rotation axis of the polishing platen. The polishing device may comprise an actuator, such as an electric motor, for rotating the specimen holder. The actuator can be configured to rotate the specimen holder, for example, at a rotational speed of 0-150 rpm. The actuator can be configured to adjust the rotational speed of the specimen holder based on the values of the measured physical quantity. For example, in a case where the friction exceeds a predetermined threshold value or the moisture falls below a predetermined threshold value, the actuator can be configured to reduce the rotational speed of the specimen holder.
The device according to the invention can measure the physical quantity, which is indicative of the moisture or the friction, in a plurality of positions on the polishing pad and, based on the values of the measured physical quantity, dispense the polishing suspension to the plurality of positions on the polishing pad.
The means for measuring the physical quantity may comprise one or more movable sensors, or a plurality of fixed (non-movable) sensors arranged at a predetermined distance from each other. The sensor can be a moisture sensor, which can measure, for example, the (electrical) resistance on the polishing pad or the capacitance between the opposite sides of the polishing pad (i.e. the capacitance over the thickness of the polishing pad), which both vary as a function of the moisture in the polishing pad. The sensor can also be a force sensor, which is configured to measure the friction on the surface of the polishing pad. The measurement of the friction can be based on detecting the lateral force acting on an object that is arranged in contact with the surface of the polishing pad.
The means for dispensing the polishing suspension may comprise one or more movable spray nozzles, or a plurality of fixed (non-movable) spray nozzles arranged at a predetermined distance from each other. The means for dispensing the polishing suspension may also comprise a container for the polishing suspension. Alternatively, the means for dispensing the polishing suspension may comprise a plurality of containers for the polishing suspension or for different polishing suspensions. The container(s) can be connected by flexible hoses to the spray nozzles.
The means for dispensing the polishing suspension may comprise a control unit for controlling the spray nozzles. The control unit may comprise a processor and a memory including computer program code, the memory and the computer program code being configured to, with the processor, cause the spray nozzles to dispense suitable amounts of the polishing suspension to the plurality of positions on the polishing pad. The amount of the polishing suspension to be dispensed to each position is determined based on the values of the measured physical quantity. The values of the measured physical quantity can be compared to a predefined reference value or profile in order to determine the amount of the polishing suspension to be dispensed. The predefined reference value or profile corresponds to the desired moisture content in the polishing pad. The amount of the polishing suspension to be dispensed to each position on the polishing pad can be, for example, less than 5 μl/cm2, less than 2 μl/cm2 or 0.5-2 μl/cm2.
The polishing suspension enhances the polishing action and prevents overheating during the polishing process. The polishing suspension contains water and/or other suitable liquids, such as alcohols (e.g. ethanol, glycol or isopropyl alcohol) for moistening, cooling and lubricating the polishing pad. The polishing suspension may also contain abrasive particles, such as diamonds, aluminium oxide or colloidal silica for polishing of the surface of the specimen. Typically, the polishing suspension (i.e. slurry or fluid) is a mixture of liquid(s) and abrasive(s).
An advantage of the device according to the invention is that it can provide and maintain a substantially constant and uniform moisture content in the polishing pad during the polishing process. Another advantage of the device according to the invention is that it enables to achieve a uniform and high-quality polishing result of the specimen. Still another advantage of the device according to the invention is that it enables to optimize (minimize) the consumption of the polishing suspension in the polishing process.
According to an embodiment of the invention the physical quantity is the resistance on the polishing pad and the means for dispensing a polishing suspension is configured to dispense the polishing suspension to a position on the polishing pad if in said position the value of the resistance is larger than a first threshold value. The resistance on the polishing pad varies as a function of the moisture in the polishing pad. The wetter the polishing pad is, the smaller the resistance is.
According to an embodiment of the invention the physical quantity is the capacitance between the opposite sides of the polishing pad and the means for dispensing a polishing suspension is configured to dispense the polishing suspension to a position on the polishing pad if in said position the value of the capacitance is smaller than a second threshold value. The capacitance between the opposite sides of the polishing pad varies as a function of the moisture in the polishing pad. The wetter the polishing pad is, the larger the capacitance is.
According to an embodiment of the invention the physical quantity is the friction on the surface of the polishing pad and the means for dispensing a polishing suspension is configured to dispense the polishing suspension to a position on the polishing pad if in said position the value of the friction is larger than a third threshold value. The friction on the surface of the polishing pad varies as a function of the moisture in the polishing pad. The wetter the polishing pad is, the smaller the friction is.
According to an embodiment of the invention the means for measuring a physical quantity comprises a sensor arranged in contact with the surface of the polishing pad and means for moving the sensor between the plurality of positions on the polishing pad. The means for moving the sensor is configured to move the sensor along the surface of the polishing pad. The sensor can be a moisture sensor, which measures the resistance on the polishing pad and/or the capacitance vertically between the opposite sides of the polishing pad. The sensor can alternatively be a force sensor, which measures the friction on the surface of the polishing pad.
According to an embodiment of the invention the means for moving the sensor comprises an arm arranged above the polishing pad and an actuator for moving the sensor along the arm. The arm is preferably straight, and its longitudinal axis is arranged parallel to the plane of the polishing pad. The arm is preferably arranged above the polishing pad in such a manner that it extends from the centre to the periphery of the polishing pad. This enables the sensor to be moved to all possible positions on the polishing pad as the polishing platen is rotated. The actuator can be an electric motor.
According to an embodiment of the invention the means for moving the sensor is the specimen holder that is configured to hold the sensor against the polishing pad. The specimen holder can comprise, for example, an insert in which the sensor can move freely or is secured by clamping. The sensor may comprise a wireless transmitter or transceiver for communicating with a remote device, such as a measuring instrument and/or a control unit that controls the spray nozzle(s).
According to an embodiment of the invention the means for measuring a physical quantity comprises an array of sensors arranged in contact with the surface of the polishing pad. The sensors can be attached to an arm that is arranged above the polishing pad. Preferably, the sensors are attached to the arm at a predetermined distance from each other. The arm is preferably straight, and its longitudinal axis is arranged parallel to the plane of the polishing pad. The arm is preferably arranged above the polishing pad in such a manner that it extends from the centre to the periphery of the polishing pad. The number of sensors depends on the diameter of the polishing pad and the needed measurement accuracy, and it can be, for example, less than 100, less than 50, less than 20, or 6-12. The sensors can be moisture sensors, which measure the resistance on the polishing pad and/or the capacitance between the opposite sides of the polishing pad. The sensors can alternatively be force sensors, which measure the friction on the surface of the polishing pad.
According to an embodiment of the invention the sensor comprises at least two electrical contact elements arranged in contact with the surface of the polishing pad, and the means for measuring a physical quantity comprises means for measuring the resistance between two of the at least two electrical contact elements. The electrical contact elements, i.e. the electrodes, provide an electrical path through which electrical properties of the polishing pad can be measured. The electrical contact elements can have different shapes and sizes. The electrical contact elements are made of an electrically conductive material, which is preferably also wear and corrosion resistant. Preferable materials for the electrical contact elements are, for example, stainless steel and tool steel. The electrical contact elements are electrically isolated from each other to prevent short circuits. The means for measuring the resistance between two of the at least two electrical contact elements may comprise a measuring instrument that is electrically connected with electrical connections, such as wires, cables or carbon brushes, to two electrical contact elements of the sensor. The measuring instrument is configured to measure the resistance between these two electrical contact elements.
According to an embodiment of the invention the means for measuring a physical quantity comprises means for measuring the capacitance between one of the at least two electrical contact elements and the polishing platen. The means for measuring the capacitance between one of the at least two electrical contact elements and the polishing platen may comprise a measuring instrument that is electrically connected with electrical connections, such as wires, cables or carbon brushes, to the electrical contact element and the polishing platen. The measuring instrument is configured to measure the capacitance between the electrical contact element and the polishing platen. A resistor can be used between the measuring instrument and the polishing platen to reduce interference.
According to an embodiment of the invention the means for measuring a physical quantity comprises a compression element for pressing the sensor against the surface of the polishing pad. The compression element enables to keep the sensor in contact with the surface of the polishing pad with a suitable pressing force. The pressing force of the compression element can be adjustable. The compression element can be, for example, a spring. The compression element can utilize air pressure, gravity, or magnetic or electromagnetic force in producing the suitable pressing force.
According to an embodiment of the invention the means for measuring a physical quantity comprises means for measuring the lateral force acting on the sensor. The means for measuring the lateral force may comprise a force sensor that is attached to the sensor.
According to an embodiment of the invention the means for measuring a physical quantity comprises a contactless moisture sensor arranged above the polishing pad and means for moving the contactless moisture sensor between the plurality of positions on the polishing pad. The contactless moisture sensor can measure the moisture in the polishing pad. The contactless moisture sensor can be, for example, an optical sensor. The means for moving the contactless moisture sensor may comprise an arm arranged above the polishing pad and an actuator for moving the contactless moisture sensor along the arm.
According to an embodiment of the invention the means for measuring a physical quantity comprises an array of contactless moisture sensors arranged above the polishing pad. The contactless moisture sensors can measure the moisture in the polishing pad. The contactless moisture sensors can be, for example, optical sensors. The contactless moisture sensors can be attached to an arm that is arranged above the polishing pad. Preferably, the contactless moisture sensors are attached to the arm at a predetermined distance from each other.
According to an embodiment of the invention the contactless moisture sensor is a spectrometer that is configured to measure the intensity of light reflected from the surface of the polishing pad as a function of the wavelength. The intensity of the reflected light depends on the moisture in the polishing pad. Depending on the used polishing suspension and the material of the polishing pad, the intensity of the reflected light at a certain wavelength can act quite differently as the moisture in the polishing pad changes. For example, when the moisture in the polishing pad decreases, the intensity of the reflected light can increase at one wavelength and decrease at the other wavelength. The spectrometer may comprise a plurality of optical detectors, each of them being adapted to detect light at a different wavelength. The wavelength range of the spectrometer can be, for example, 400-700 nm, 300-1000 nm or 750-2500 nm. Preferably, the distance between the spectrometer and the surface of the polishing pad is kept constant during the measurement. The surface of the polishing pad can be illuminated with one or more light sources, such as a light-emitting diode (LED).
According to an embodiment of the invention the contactless moisture sensor is a polymer membrane. The resistance of the polymer membrane depends on the moisture. The moisture in the polishing pad can be measured by arranging the polymer membrane close to the surface of the polishing pad. For the measurement of the resistance, the polymer membrane can be provided with two electrical contact elements. The polymer membrane is preferably attached to a substrate, such as a glass piece.
According to an embodiment of the invention the device comprises means for measuring the temperature of the sensor and/or the polishing pad, and means for adjusting the rotational speed of the polishing platen and/or the specimen holder based on a value of the measured temperature. The means for measuring the temperature may comprise contact and/or contactless temperature sensors.
According to an embodiment of the invention the device comprises means for measuring the vibration of the sensor and means for adjusting the rotational speed of the polishing platen and/or the specimen holder based on a value of the measured vibration. The means for measuring the vibration may comprise a vibration sensor that is attached to the sensor.
According to an embodiment of the invention the device comprises means for cooling the polishing platen. The polishing platen can be cooled by spraying water onto the bottom side of the polishing platen. The device may comprise a splash guard to prevent the mist of cooling water escaping onto the polishing pad. The splash guard can be made of, for example, plastic.
According to an embodiment of the invention the means for dispensing a polishing suspension comprises a spray nozzle arranged above the polishing pad and means for moving the spray nozzle between the plurality of positions on the polishing pad. The means for dispensing a polishing suspension may comprise one or more containers for the polishing suspension or for different polishing suspensions. The container can be connected, for example, by a flexible hose to the spray nozzle.
According to an embodiment of the invention the means for moving the spray nozzle comprises an arm arranged above the polishing pad and an actuator for moving the spray nozzle along the arm. The arm is preferably straight, and its longitudinal axis is arranged parallel to the plane of the polishing pad. The arm is preferably arranged above the polishing pad in such a manner that it extends from the centre to the periphery of the polishing pad. This enables the spray nozzle to be moved to all possible positions on the polishing pad as the polishing platen is rotated. The actuator can be an electric motor.
According to an embodiment of the invention the means for moving the spray nozzle is the specimen holder to which the spray nozzle is attached.
According to an embodiment of the invention the means for dispensing a polishing suspension comprises an array of spray nozzles arranged above the polishing pad. The spray nozzles can be attached to an arm. Preferably, the spray nozzles are attached to the arm at a predetermined distance from each other. The arm is preferably straight, and its longitudinal axis is arranged parallel to the plane of the polishing pad. The arm is preferably arranged above the polishing pad in such a manner that it extends from the centre to the periphery of the polishing pad. The number of spray nozzles depends on the diameter of the polishing pad, and it can be, for example, less than 100, less than 50, less than 20, or 6-12. The means for dispensing a polishing suspension may comprise one or more containers for the polishing suspension or for different polishing suspensions. The container(s) can be connected, for example, by flexible hoses to the spray nozzles.
According to an embodiment of the invention the device comprises means for evaporating the polishing suspension from the polishing pad. The polishing suspension can be evaporated with a stream of compressed air to a desired position on the polishing pad.
The present invention also relates to a method for polishing a specimen. The method according to the invention comprises holding the specimen with a specimen holder against a polishing pad that is attached to a polishing platen, rotating the polishing platen about an axis, measuring a physical quantity indicative of the moisture or the friction in a plurality of positions on the polishing pad, and dispensing a polishing suspension, based on values of the measured physical quantity, to the plurality of positions on the polishing pad.
An advantage of the method according to the invention is that it can provide and maintain a substantially constant and uniform moisture content in the polishing pad during the polishing process. Another advantage of the method according to the invention is that it enables to achieve a uniform and high-quality polishing result of the specimen. Still another advantage of the method according to the invention is that it enables to consume less polishing suspension during the polishing process.
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.
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.
The polishing device comprises a moisture sensor 107 for detecting the moisture in the polishing pad 103. The moisture sensor 107 comprises electrical contact elements 108 and 109, which are arranged in contact with the surface of the polishing pad 103. The electrical contact elements 108 and 109 provide an electrical path through which electrical properties of the polishing pad 103 can be measured. The electrical contact elements 108 and 109 are electrically connected to a measuring instrument 110 that can measure the resistance between the electrical contact elements 108 and 109. The resistance between the electrical contact elements 108 and 109 is indicative of the moisture in a measurement position on the polishing pad 103. The measuring instrument 110 is electrically connected to the polishing platen 101, thus allowing to measure the capacitance between one of the electrical contact elements 108, 109 and the polishing platen 101, i.e. between the opposite sides of the polishing pad 103. The capacitance between the electrical contact element 108 or 109 and the polishing platen 101 is indicative of the moisture in a measurement position on the polishing pad 103.
The moisture sensor 107 is attached with a rod 111 to an arm 112 that is located above the polishing pad 103. The arm 112 extends from the centre to the periphery of the polishing pad 103. The moisture sensor 107 can be moved with an actuator 113 along the arm 112, thus enabling to move the moisture sensor 107 between different positions on the polishing pad 103. The rod 111 is provided with a spring 114 for pressing the moisture sensor 107 against the surface of the polishing pad 103. The spring 114 enables to keep the electrical contact elements 108 and 109 in contact with the surface of the polishing pad 103 with a suitable pressing force.
The polishing device comprises a force sensor 115 for detecting the lateral force acting on the moisture sensor 107. The force sensor 115 is attached to the rod 111 and electrically connected to the measuring instrument 110 that can determine the lateral force, i.e. the friction on the surface of the polishing pad 103. The friction on the surface of the polishing pad 103 is indicative of the moisture in a measurement position on the polishing pad 103.
The polishing device comprises a spray nozzle 116 for dispensing a polishing suspension on the polishing pad 103. The spray nozzle 116 is attached to an arm 117 that is located above the polishing pad 103. The arm 117 extends from the centre to the periphery of the polishing pad 103. The spray nozzle 116 can be moved with an actuator 118 along the arm 117, thus enabling to move the spray nozzle 116 between different positions above the polishing pad 103.
The polishing suspension is stored in a container 119 from which it is conveyed through a flexible hose 120 to the spray nozzle 116 to be dispensed on the polishing pad 103. The polishing device comprises a control unit 121 for controlling the dispensing of the polishing suspension. The control unit 121 controls the spray nozzle 116 to dispense suitable amounts of the polishing suspension to desired positions on the polishing pad 103. The amount of the polishing suspension to be dispensed to each position is determined based on the determined moisture or the friction on each position.
The polishing device comprises a temperature sensor 122 attached to the electrical contact element 108 for measuring the temperature of the electrical contact element 108, and a temperature sensor 123 attached to the arm 112 for contactlessly measuring the temperature of the polishing pad 103. The polishing device also comprises a vibration sensor 124 attached to the rod 111 for measuring the vibration of the moisture sensor 107. The control unit 121 can control the rotational speeds of the polishing platen 101 and the specimen holder 105 based on the measured temperatures and/or vibration.
The polishing device comprises a spray nozzle 125 for spraying water onto the bottom side of the polishing platen 101 in order to cool the polishing platen 101. A splash guard 126 is used to prevent the mist of water escaping onto the polishing pad 103.
The polishing device comprises three moisture sensors 207 for detecting the moisture in the polishing pad 203. The moisture sensors 207 are arranged at regular intervals from each other and attached with rods 208 to an arm 209 that is located above the polishing pad 203. The arm 209 extends from the centre to the periphery of the polishing pad 203.
Each of the moisture sensors 207 comprises electrical contact elements 210 and 211, which are arranged in contact with the surface of the polishing pad 203. The electrical contact elements 210 and 211 provide an electrical path through which electrical properties of the polishing pad 203 can be measured. The electrical contact elements 210 and 211 are electrically connected to a measuring instrument 212 that can measure the resistance between the electrical contact elements 210 and 211. The resistance between the electrical contact elements 210 and 211 is indicative of the moisture in a measurement position on the polishing pad 203. The measuring instrument 212 is electrically connected to the polishing platen 201, thus allowing to measure the capacitance between one of the electrical contact elements 210, 211 and the polishing platen 201, i.e. between the opposite sides of the polishing pad 203. The capacitance between the electrical contact element 210 or 211 and the polishing platen 201 is indicative of the moisture in a measurement position on the polishing pad 203.
The polishing device comprises three spray nozzles 213 for dispensing a polishing suspension on the polishing pad 203. The spray nozzles 213 are attached at regular intervals to an arm 214 that is located above the polishing pad 203. The arm 214 extends from the centre to the periphery of the polishing pad 203.
The polishing suspension is stored in a container 215 from which it is conveyed through flexible hoses 216 to the spray nozzles 213 to be dispensed on the polishing pad 203. The polishing device comprises a control unit 217 for controlling the dispensing of the polishing suspension. The control unit 217 controls the spray nozzles 213 to dispense suitable amounts of the polishing suspension to desired positions on the polishing pad 203. The amount of the polishing suspension to be dispensed to each position is determined based on the determined moisture.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20195982 | Nov 2019 | FI | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FI2020/050764 | 11/16/2020 | WO |
