Balancing system for a rotating spindle of a machine tool and related control method

Abstract

A balancing system for a rotating spindle (3) of a machine tool (1); the balancing system having a rotating part including a balancing head (7) having at least one balancing weight (8) and at least one motor (9) suitable for adjusting the position of the balancing weight; the rotating part also comprising a vibration sensor (10) and a control system (11), the control system (11) having at least one hardware (12) and at least one software (13) executed by the hardware; the balancing system also comprising a two-way contactless communication system (14) establishing communication between the rotating control system and fixed processing and control electronics (15) connected to a machine tool control unit (20). The software of the control system is characterized by a management application (19) and a service application (18), the management application (19) performing all management of the balancing head and the vibration sensor during normal operation, and the service application (18) automatically starting and starting the management application when the control system is powered on after a power interruption, or, if a software update is required, overwriting the existing version of the management application with the new version.

Description

Technical Field

[0001] The present invention relates to a balancing system for a rotating spindle of a machine tool and a related control method Background Art

[0002] For example, in the patent applications EP0690979A1, EP1870198A1 and EP3134980A1 a balancing system for a rotating spindle (hub) of a machine tool, in particular a grinding machine, is described, wherein the spindle rotates relative to a frame and supports (at least) one grinding wheel. The balancing system comprises a rotating part having a balancing head, which is usually accommodated in an axial opening of the spindle, substantially corresponding to the grinding wheel, or is arranged at one end of the spindle, also axially aligned. The balancing head comprises at least one balancing weight eccentric to the axis of rotation, the position of which is adjustable and controlled, for example, by an electric motor.

[0003] Typically, the rotating part also carries a vibration sensor, usually associated with the balancing head and physically integrated therein for practical reasons, for detecting the ultrasonic emissions emitted by the contact between the grinding wheel and the workpiece or between the grinding wheel and the dressing tool (dresser). The electrical signal generated by the vibration sensor

[0004] Used (in a known manner) to control the duty cycle.

[0005] In the rotating part there is the electronics or control system which supervises the operation of the balancing head and the vibration sensor and consists of hardware (usually a microcontroller equipped with memory) and software (which is stored in the memory of the microcontroller or in an external memory accessible to the microcontroller).

[0006] A two-way contactless communication system is provided for transmitting analog and / or digital information between a rotating part (specifically a control system) and processing and control electronics which are in a fixed position relative to the frame of a machine tool and which are in turn connected to the control unit of the machine tool. Specifically, the communication system is used by the processing and control electronics to send control signals to the control system of the rotating part (e.g. for activating / deactivating the readings of a vibration sensor, or for driving an electric motor that moves a balancing weight), and for sending diagnostic signals and the readings of the vibration sensor to the processing and control electronics in the opposite direction. The analog electrical signals provided by the vibration sensor can be processed and digitized on the rotating part, or can be transmitted in analog form and processed and digitized in the processing and control electronics. The second option, although requiring greater system complexity, is generally preferred because it offers greater flexibility.

[0007] A contactless power transmission system is provided to supply necessary power to a control system present in a rotating part. Generally, the power transmission system includes an air-core transformer having a primary winding arranged in an assembly fixed to a machine tool frame and a secondary winding arranged in the rotating part.

[0008] Sometimes it is necessary to update the software of the control system of the rotating part, and since such an update operation providing a complete overwriting of the contents contained in the memory requires tooling, it is relatively long and complex. Specifically, in order to update the software of the control system of the rotating part, the rotating part must be disassembled from the spindle to physically connect the control system hardware (i.e., by a cable) to an external computer, which overwrites the contents contained in the memory with the new version of the software. Once the overwriting is completed, the rotating part must be reassembled.

[0009] Furthermore, in the known balancing systems, the diagnostics that can be provided by the balancing head are limited. In particular, the communication channel defined by the bidirectional contactless communication system, which is used to transmit the readings of the vibration sensors in analog form from the rotating part to the processing and control electronics, cannot be used to transmit any digital diagnostic signals generated by the control system of the rotating part when the spindle is used to perform machining with the corresponding grinding wheel. The control system is therefore only able to respond to any diagnostic queries from the processing and control electronics when the spindle is not in operation. Summary of the invention

[0010] The object of the present invention is to provide a balancing system for a rotating spindle of a machine tool and a related control method, which balancing system does not have the above-mentioned disadvantages and is at the same time easy to manufacture and low-cost.

[0011] According to the present invention, there is provided a balancing system for a rotating spindle of a machine tool and an associated control method in accordance with what is claimed in the accompanying claims.

[0012] The claims describe embodiments of the invention which form an integral part of the present description. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention will now be described with reference to the accompanying drawings, which relate to embodiments and are given as non-limiting examples, in which:

[0014] - Figure 1 is a schematic and partially sectional view of a machine tool provided with a rotating spindle supporting a grinding wheel and equipped with a balancing system; and

[0015] - Figure 2 A block diagram of a portion of the control components and associated software of a balancing system. DETAILED DESCRIPTION

[0016] exist Figure 1In the drawing, a machine tool, in particular a grinding machine, is shown schematically and partially and is denoted by reference numeral 1 .

[0017] The machine tool 1 comprises a frame 2 which rotatably supports a spindle 3 by means of interposed bearings (not shown) so that the latter can rotate about an axis of rotation 4 .

[0018] The spindle 3 supports a grinding wheel 5 by means of a corresponding grinding wheel hub, which is removably fixed to the spindle 3 by means known and not shown, including, for example, a cone clutch. The spindle 3 and the grinding wheel hub define the rotating part of the machine tool 1. The spindle 3 has a central axial opening 6, in which the rotating part of the balancing system with a balancing head 7 is accommodated. The balancing head 7 is of a known type and comprises two balancing masses 8 eccentric to the axis of rotation 4, and an associated electric motor 9 for adjusting the angular position of the balancing masses 8. A vibration sensor 10 (i.e. an acoustic sensor) is also associated with the balancing head 7 and is generally considered to be part of the balancing system.

[0019] In a preferred embodiment and for practical reasons, the vibration sensor 10 associated with the balancing head 7, in particular integrated therewith, may be arranged differently in the rotating part.

[0020] A balancing system with a balancing head 7 and a vibration sensor 10 generally has two functions: balancing the grinding wheel 5, which is performed each time the grinding wheel 5 is changed, before the grinding wheel 5 is actually used to perform machining, and when necessary or deemed appropriate during the service life of the grinding wheel, and process monitoring by means of the vibration sensor 10 associated with the balancing head 7.

[0021] At this point, it is important to note that the spindle 3 is balanced by the manufacturer, while the grinding wheel 5 mounted thereon is usually unbalanced, and during its service life, the unbalance of the grinding wheel 5 varies. Therefore, the balancing head 7 is integrally formed with the grinding wheel 5 so that the former can quickly correct the unbalance of the latter when necessary, which has a great impact on the production efficiency of the machine tool 1 and the quality of the workpiece.

[0022] The balancing system comprises a control system 11 for controlling the rotating part, which supervises the operation of the balancing head 7 and the associated vibration sensor 10 and consists of hardware 12 (usually a microcontroller equipped with memory) and software 13, the latter being stored in the memory of the microcontroller.

[0023] The balancing system also comprises a fixed part with processing and control electronics 15 supported by the frame 2 of the machine tool 1 and connected to a control unit 20 of the machine tool 1 .

[0024] A two-way contactless communication system 14 is provided between the rotating part and the fixed part of the balancing system, the communication system being suitable for establishing communication between the control system 11 and the processing and control electronics 15 for the transmission of analog and digital information. The communication system 14 is preferably of optical type and comprises a first transceiver device 16 in the fixed part, coupled to the frame 2 of the machine tool 1 and connected to the processing and control electronics 15 by a cable (not shown) and a second transceiver device 17 in the rotating part, facing the first transceiver device 16 and connected to the control system 11 by a coiled cable housed in the axial opening 6.

[0025] The communication system 14 is made in a known manner, for example according to one of the alternatives described in the aforementioned patent application EP 0 690 979 A1, and is not described in detail here.

[0026] The communication system 14 is used by the processing and control electronics 15 to send digital control signals to the control system 11 of the rotating part (for example for activating / deactivating the readings of the vibration sensor 10, or for driving the electric motor 9 for moving the balancing weight 8), and is used by the control system 11 of the rotating part to send digital diagnostic signals and readings of the vibration sensor 10, usually in analog form, to the processing and control electronics 15 in the opposite direction.

[0027] A wireless power transmission system (usually integrated with a communication system 14) is provided to provide the necessary power to the control system 11 of the rotating part. Typically, the power transmission system comprises an air-core transformer having a primary winding arranged in an assembly fixed to the frame 2 of the machine tool 1 (for example integrated in a first transceiver device 16) and a secondary winding arranged in a rotating part connected to the spindle 3 (for example integrated in a second transceiver device 17).

[0028] like Figure 2As shown, the software 13 of the control system 11 includes a service application 18 and a management application 19, both of which are configured to interface with the processing and control electronics 15 independently of each other via the communication system 14. The service application 18 is configured to perform a limited number of tasks only when the rotating component (specifically the control system 11) receives power (i.e., is turned on), while the management application 19 (which constitutes the firmware of the balancing head 7) is configured to perform all management of the balancing head 7 and the associated vibration sensor 10 during normal operation. In particular, when the control system 11 is powered on, or receives power after an interruption or after a period of power failure (i.e., when powered on), only the service application 18 is automatically started and is configured to perform the necessary steps to start the normal operation of the balancing system or to perform a software update according to the commands received from the processing and control electronics 15. In particular, if the balancing system must operate normally, the service application 18 starts the management application 19 and stops until the next startup. On the contrary, if a software update needs to be performed, the service application 18 does not start the management application 19, and

[0029] The service application 18 is prepared to receive the code packets from the processing and control electronics 15 code (via the communication system 14). The service application 18 writes the code packets into the memory of the hardware 12 by overwriting the previous, existing version of the management application 19, which obviously cannot be started before the update is completed. More specifically, when the update is completed, the service application 18 can be stopped after starting the management application 19, or the control system 11 can be shut down. During the machine work in which the grinding wheel 5 is in contact with the workpiece being machined, or during the maintenance of the grinding wheel 5 in which the grinding wheel 5 is in contact with the dressing tool (dresser), the management application 19 of the software of the control system 11 uses the communication system 14 to continuously transmit (preferably in analog form) the readings of the vibration sensor 10. At the same time, the management application 19 cyclically reads the current value of one or more parameters of the rotating part through one or more sensors (for example, one or more temperature sensors detecting the temperature of the rotating part) present in the rotating part (for example, in the balancing head 7 and / or in the hardware 12 and / or in the second transceiver device 17) and checks whether the current value of the parameter (or parameters) is within an acceptable value range. If the current value of at least one parameter (e.g. the temperature value of the rotating part) clearly exceeds the range of corresponding acceptable values ​​(e.g. if the detected temperature is too high), the management application 19 stores a record of the detected anomaly in the memory of the hardware 12 and interrupts the transmission of the reading of the vibration sensor 10. When the reading of the vibration sensor 10 is interrupted, the processing and control electronics 15 generates an alarm and sends it to the control unit 20 of the machine tool 1, which control unit 20 can decide to immediately stop the ongoing operation based on the provisions of the relevant control program. In addition, the processing and control electronics 15 requests the control system 11 of the rotating part (more specifically the management application 19) to restart the analog reading of the vibration sensor 10. In response to this request from the processing and control electronics 15, the management application 19 is programmed not to restart the analog reading of the vibration sensor 10, but to transmit the anomaly just recorded in digital form, and therefore, the analog reading of the vibration sensor 10 is interrupted, and the final decision on how to proceed is then delegated to the processing and control electronics 15.

[0030] What has been described so far refers to the preferred case of transmitting the readings of the vibration sensor 10 in analog form. If, on the other hand, the readings of the vibration sensor 10 are processed and digitized in the rotating part and sent digitally to the processing and control electronics 15, it is possible to associate this transmission with a digital signal which identifies the anomaly immediately when it is detected. Thus, in this case, the transmission of the readings of the vibration sensor 10 is not interrupted and it is optional to write a record of the anomaly to the memory of the hardware 12, which record is still useful for subsequent processing.

[0031] In the embodiment shown in the figures, the control system 11 of the rotating part comprises a single piece of hardware 12 (i.e. a single microcontroller). According to other embodiments not shown, the control system 11 of the rotating part has a modular architecture with a plurality of pieces of hardware 12, typically two or three pieces of hardware 12 (i.e. two or three microcontrollers), which are physically separated from each other and connected to each other, for example, via a BUS communication channel. In this case, all the pieces of hardware 12 of the control system 11 have a similar structure and are controlled by the same type of software 13, which is divided into its own service applications 18 and management applications 19.

[0032] In the embodiment shown in the figures, the spindle 3 of the machine tool 1 supports a single grinding wheel 5. According to another embodiment not shown, the spindle 3 of the machine tool 1 supports two grinding wheels 5, which are arranged at opposite ends of the spindle 3.

[0033] In the embodiment shown in the figures, the balancing system comprises a rotating part with a single balancing head 7. According to another embodiment not shown, the rotating part of the balancing system comprises several balancing heads 7. For example, in an embodiment comprising a single grinding wheel 5 or two different grinding wheels 5, two balancing heads 7 can be arranged at opposite ends of the spindle 3.

[0034] As mentioned previously, the balancing head 7 is equipped with two balancing masses 8 (e.g. coplanar masses) which can rotate about the axis of rotation 4 of the spindle 3 in order to compensate for the imbalance present in the grinding wheel 5. If it is sufficient to correct the imbalance in only one plane, one balancing head 7 is sufficient. In some cases, it is necessary to correct the imbalance on both sides of the spindle 3, so it is necessary to use two balancing heads 7 appropriately coordinated and arranged at opposite ends of the spindle 3.

[0035] The use of a single balancing head 7 means the manipulation of two balancing masses 8 , whereas the use of two balancing heads 7 means the manipulation of four balancing masses 8 (two balancing masses 8 per balancing head 7 ).

[0036] There are basically two strategies for balancing the grinding wheel 5: heuristic and deterministic. The heuristic strategy is based on the execution of actions, the observation of the results, and the planning of the next action until the imbalance is eliminated or the imbalance is reduced below a predetermined threshold, which is detected by at least one specific vibration sensor (low frequency) (not shown in the figure) and connected to the frame 2 of the machine tool 1 in a known manner. If an action is taken in the direction of reducing the imbalance (for example, a specific movement of the balancing mass 8), it will be carried out in the same direction, otherwise it will produce a different effect. The deterministic strategy is based on the calculation of the imbalance vector and therefore on the calculation of the position of the balancing mass 8 of the balancing head 7 (or multiple balancing heads 7) that must be adopted to eliminate the imbalance. In order to implement this type of strategy, it is necessary to know the position of the balancing mass 8 of the balancing head 7 accurately (for example, the angular position), which can be obtained by using appropriate position sensors or other devices (for example, angular encoders).

[0037] If a heuristic strategy is used, a position sensor or encoder in the balancing head 7 is not necessary, but a "neutral" or "home" sensor capable of detecting when the balancing mass 8 of the balancing head 7 is in a position causing zero imbalance on the rotating part is useful.

[0038] These two strategies can be combined with each other, for example, in a balancing process comprising a first phase in which a deterministic type strategy is employed to significantly reduce the imbalance and a second refinement phase in which a heuristic type strategy allows further reduction and significant elimination of the remaining imbalance.

[0039] A control system 11 capable of driving more balancing heads 7 (eg two balancing heads) by adopting two possible strategies makes the system more flexible and easier to adapt to specific application requirements.

[0040] There are two main ways of driving the electric motor 9 which moves the balancing masses 8 of the same balancing head 7 under the control of the control system 11 of the rotating part. More specifically, the two balancing masses 8 can be moved simultaneously or alternately, i.e. one at a time. If the rotating part of the application has two balancing heads 7 on the same spindle 3, the same principle applies, i.e. the two balancing heads 7 can be driven by the control system 11 simultaneously or alternately.

[0041] Depending on the combination used, one or more (from a minimum of one to a maximum of four) balancing masses 8 can be moved simultaneously.

[0042] Another aspect of the balancing system according to the invention is the possibility to easily vary the bandwidth and the gain, which simplifies the configuration of the application of the processing and control electronics 15 that processes the analog signal provided by the vibration sensor 10 and improves its effectiveness.

[0043] The balancing system according to the invention can be embodied differently with respect to what is schematically shown in the figures and described so far. The control system 11 can, for example, be partially or completely integrated in the second transceiver device 17 or formed integrally therewith, connected to the balancing head 7 via a coiled cable. A different alternative consists in realizing the rotating part as a monolithic piece, i.e. in this case, the second transceiver device 17, the control system 11 and the balancing head 7 are parts of a single element or parts of elements rigidly connected to each other, and there is no coiled cable.

[0044] As mentioned above, the rotating part of the balancing system according to the invention can be realized in a single piece and can also be arranged at one end of the main shaft 3 instead of being accommodated in the axial opening 6 of the main shaft 3 .

[0045] According to other embodiments of the present invention that are not shown, the spindle 3 of the machine tool 1 may be equipped with a rotating tool other than the grinding wheel 5 .

[0046] The embodiments described herein may be combined with each other without departing from the scope of the present invention.

[0047] The control method described above has many advantages.

[0048] Firstly, the control method described above allows updating the software 13 of the control system 11 of the rotating part in a simple and rapid manner, since the software 13 update is performed without any physical intervention by an operator disassembling and reassembling the mechanical parts, and connecting and disconnecting them electrically using cables and appropriate connectors. In other words, the management application 19 (i.e. the firmware of the balancing head 7) can be updated directly by the processing and control electronics 15, without any physical intervention by an operator, and more specifically interventions that could be complex and delicate interventions that inevitably slow down the update process significantly and therefore prolong the period of inoperability of the machine tool.

[0049] At this point, it is important to note that the service application 18 does not require any kind of updating, since it performs only two simple and fast tasks, and therefore, there is no real advantage in making the service application 18 faster and / or more efficient, since it is sufficient that the service application 18 is effective, i.e., it performs the two tasks mentioned above correctly. Of course, if necessary, the service application 18 can in any case be updated by disassembling the hardware 12 in order to physically connect the latter to an external computer.

[0050] Having a diagnostic function that is always active and therefore able to promptly communicate to the control system 11 the occurrence of faults or environmental phenomena that could damage the rotating parts (and therefore, the spindle 3 and / or the grinding wheel 5) increases the reliability of the application and the machine tool 1. Prompt knowledge of the occurrence of faults or potential problems can prevent serious damage to the spindle 3 and / or the grinding wheel 5. If the environment changes (for example, the temperature inside the spindle 3 increases, which could cause damage to the system), the rapid transmission of this information to the processing and control electronics 15 allows the control unit 20 of the machine tool 1 to take action to prevent damage.

[0051] Finally, the control method described above can be implemented without any additional costs, since the software 13 consisting of the two applications 18 and 19 does not require any additional or more execution hardware than is usually employed in known balancing systems.

[0052] A fixed control system having hardware (e.g., a microcontroller) and software may be provided in the fixed part (e.g., in the processing and control electronics 15), and such software may include service applications and management applications having features and operating methods similar to the features and operating methods of the above-mentioned service applications 18 and management applications 19 of the software 13 in the control system 11 of the rotating part.

Claims

1. A balancing system, the balancing system being used for a rotating spindle (3) of a machine tool (1), the balancing system comprising: • a rotating part connected to the spindle (3) and comprising At least one balancing head (7), the balancing head (7) having at least one balancing mass (8) arranged eccentrically with respect to the axis of rotation (4), and at least one electric motor (9) adapted to adjust the position of the balancing weight (8); · at least one vibration sensor (10); and A control system (11) comprising at least one hardware (12) and at least one software (13) adapted to be executed by said hardware (12); • a fixed part, with processing and control electronics (15); and • a two-way contactless communication system (14) adapted to establish communication between said control system (11) of said rotating part and said processing and control electronics (15) of said fixed part; The balancing system is characterized in that the software (13) of the control system (11) comprises: - a management application (19) configured to perform overall management of the balancing head (7) and the vibration sensor (10) during normal operation; and - a service application (18) which is automatically started when the control system (11) is powered on after a power interruption and is configured to: according to a command received from the processing and control electronics (15), start the management application (19) and after starting the management application (19) the service application (18) is stopped, or to overwrite an existing version of the management application (19) with a new version of the management application (19).

2. The balancing system according to claim 1, wherein: When the control system (11) is powered on after a power outage, only the service application (18) is automatically started.

3. The balancing system according to claim 1, wherein: When the control system (11) is powered on after a power interruption, depending on the control received from the processing and control electronics (15) via the communication system (14), the service application (18) is configured to: - if the balancing system must operate normally, the management application (19) is started and the service application (18) is stopped; or - Ready to receive a code packet from the processing and control electronics (15) via the communication system (14), the service application (18) writing the code packet on the memory of the hardware (12) to overwrite the existing version of the management application (19).

4. A balancing system according to any one of claims 1, 2 or 3, wherein: The service application (18) and the management application (19) are both configured to interface with the communication system (14) independently of each other.

5. A balancing system according to any one of claims 1 to 3, for a rotating spindle (3) carrying a grinding wheel (5), wherein: The management application (19) is configured to continuously send the readings of the vibration sensor (10), preferably in analog form, to the processing and control electronics (15) using the communication system (14) during mechanical work in which the grinding wheel (5) is in contact with a workpiece being machined, or during maintenance of the grinding wheel (5) in which the grinding wheel (5) is in contact with a dressing tool.

6. The balancing system according to claim 5, wherein: The rotating part comprises at least one sensor, and the management application (19) is configured to periodically read the current value of at least one parameter of the rotating part by means of the at least one sensor during mechanical operation in which the grinding wheel (5) is in contact with a workpiece being machined, or during maintenance of the grinding wheel (5) in which the grinding wheel (5) is in contact with a dressing tool, and to check whether the current value of the parameter is within a range of acceptable values.

7. The balancing system according to claim 6, wherein: The management application (19) is configured to store a record of the detected anomaly in a memory of the hardware (12) and to interrupt the transmission of the readings of the vibration sensor (10) if the current value of the parameter is outside the corresponding range of acceptable values.

8. The balancing system according to claim 7, wherein: The management application (19) is configured to send a previously stored record of the detected anomaly to the processing and control electronics (15) after interrupting the transmission of the analog readings of the vibration sensor (10).

9. A control method for a balancing system, the balancing system being used for a rotating spindle (3) of a machine tool (1), the balancing system comprising: • a rotating part connected to the spindle (3) and comprising At least one balancing head (7), the balancing head (7) having - at least one balancing mass (8) arranged eccentrically with respect to the axis of rotation (4), and - at least one electric motor (9) suitable for adjusting the position of the balancing weight (8); · at least one vibration sensor (10); and A control system (11) comprising at least one hardware (12) and at least one software (13) suitable for being executed by said hardware (12); • a stationary part having processing and control electronics (15) connected to a control unit (20) of said machine tool (1); and • a two-way contactless communication system (14) adapted to establish communication between said control system (11) of said rotating part and said processing and control electronics (15) of said fixed part; The software (13) of the control system (11) comprises a management application (19) and a service application (18), wherein the management application (19) is configured to perform overall management of the balancing head (7) and the vibration sensor (10) during normal operation, and the service application (18) is configured to start the management application (19); when the control system (11) is powered on after a power interruption, the control method comprises the following stages: • automatically launching only said service application (18); and Based on commands received from said processing and control electronics (15), • causing the service application (18) to start the management application (19) and then stop the service application (18); and • When a software update needs to be performed, the existing version of the management application (19) is overwritten by the new version of the management application (19) through the service application (18).

10. The control method according to claim 9, wherein: When the control system (11) is powered on after the power supply interruption, depending on the control received from the processing and control electronics (15) via the communication system (14), the service application (18): If the balancing system must operate normally, the management application (19) is started and the service application (18) is stopped; or Ready to receive a code packet from the processing and control electronics (15) via the communication system (14), the service application (18) writes the code packet on the memory of the hardware (12) by overwriting the existing version of the management application (19).

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