Patent Description:
As for example it is described in patent applications <CIT>, <CIT> and <CIT>, a balancing system is known for a rotating spindle (hub) of a machine tool, in particular a grinding machine where the spindle rotates with respect to a frame and supports (at least) one grinding wheel. The balancing system includes a rotating part with a balancing head generally housed in an axial opening of the spindle substantially in correspondence to the grinding wheel, or arranged at one end of the spindle, also axially aligned. The balancing head includes at least one balancing mass eccentric with respect to the rotation axis, whose position is adjustable and is controlled, for example by an electric motor.

Generally, the rotating part carries also a vibration sensor, typically associated with the balancing head and physically integrated in it for practical reasons, for detecting ultrasonic acoustic emissions emitted by the contact between the grinding wheel and the workpiece or between the grinding wheel and a dressing tool (dresser). The electrical signals generated by the vibration sensor are used (in a known way) for controlling the working cycles.

In the rotating part there is an electronics, or control system, which superintend the operation of the balancing head and the vibration sensor and consists of a hardware (typically a microcontroller equipped with a memory) and a software (which is stored in the memory of the microcontroller or in an external memory accessible by the microcontroller).

A two-way contactless communication system is provided which transmits analog and/or digital information between the rotating part, in particular the control system, and a processing and control electronics which is in a fixed position with respect to the frame of the machine tool and is in turn connected to the control unit of the machine tool. In particular, the communication system is used by the processing and control electronics to send control signals to the control system of the rotating part (for example for activating/deactivating the reading of the vibration sensor or for driving the electrical motors that move the balancing masses) and is used in the opposite direction to send diagnostic signals and the reading of the vibration sensor to the processing and control electronics. The analog electrical signal supplied by the vibration sensor can be processed and digitized on board the rotating part or can be transmitted in analog form and processed and digitized in the processing and control electronics. The second option, while requiring greater system complexity, is generally preferred by virtue of the greater flexibility it offers.

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

Occasionally it is necessary to update the software of the control system of the rotating part and this updating operation, which provides to completely overwrite what is contained in the memory, is relatively long and complex as it requires tooling operations. In particular, 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 means of a cable - to an external computer that overwrites what is contained in the memory with the new version of the software. Once overwriting is finished, the rotating part must be reassembled.

Furthermore, in known balancing systems, the diagnostics that can be provided by the balancing head is limited. In particular, the communication channel defined by the two-way contactless communication system cannot be used to send any digital diagnostic signals generated by the control system of the rotating part when, during the use of the spindle to perform a mechanical processing through the corresponding grinding wheel, such communication channel is engaged to transmit in analog form from the rotating part to the processing and control electronics the reading of the vibration sensor. Consequently, the control system is only able to answer any diagnostic queries coming from the processing and control electronics when the spindle is not working.

The object of the present invention is to provide a balancing system for a rotating spindle of a machine tool and a relative control method, which balancing system is free from the drawbacks described above and, at the same time, is easy and cheap to manufacture.

According to the present invention, a balancing system for a rotating spindle of a machine tool and a relative control method are provided, according to what is claimed in the attached claims.

The claims describe embodiments of the present invention forming an integral part of the present description.

The present invention will now be described with reference to the attached drawings, which refers to an embodiment and are given as a non-limiting example, wherein:.

In <FIG>, a machine tool, in particular a grinding machine, is shown schematically and partially and is indicated with the reference number <NUM>.

The machine tool <NUM> comprises a frame <NUM> which rotatably supports, by interposing bearings, not shown, a spindle <NUM> so that the latter can rotate around a rotation axis <NUM>.

The spindle <NUM> supports a grinding wheel <NUM> by means of a corresponding grinding wheel hub, the latter being removably fixed to the spindle <NUM> by known and not illustrated means that comprise, for example, a cone clutch. The spindle <NUM> and the grinding wheel hub define the rotating part of the machine tool <NUM>. The spindle <NUM> has a central axial opening <NUM> in which a rotating part of a balancing system with a balancing head <NUM> is housed. The balancing head <NUM> is of a known type, and comprises two balancing masses <NUM>, eccentric with respect to the rotation axis <NUM>, and relative electric motors <NUM> for adjusting the angular position of the balancing masses <NUM>. A vibration sensor <NUM> (i.e. an acoustic sensor) is also associated with the balancing head <NUM> and is conventionally considered part of the balancing system. The vibration sensor <NUM> which, in the preferred embodiment and for practical reasons, is associated with the balancing head <NUM>, and in particular integrated with it, can be differently arranged in the rotating part.

The balancing system with the balancing head <NUM> and the vibration sensor <NUM> typically has two functions: balancing the grinding wheel <NUM>, operation that is carried out each time the grinding wheel <NUM> is replaced, before the grinding wheel <NUM> is actually used to carry out machining, and whenever it is necessary or is considered appropriate during the life of the grinding wheel, and carrying out a process monitoring through the vibration sensor <NUM> associated with the balancing head <NUM>.

In this regard it is important to note that the spindle <NUM> is balanced by the manufacturer, while the grinding wheel <NUM> which is mounted on it is typically unbalanced and during its life the unbalance of the grinding wheel <NUM> varies. Therefore, having the balancing head <NUM> integral with the grinding wheel <NUM>, so that the former can quickly correct the unbalance of the latter whenever it is needed, has a strong impact on the productivity of the machine tool <NUM> and on the quality of the workpieces.

The balancing system comprises a control system <NUM> for controlling the rotating part, which oversees the operation of the balancing head <NUM> and of the associated vibration sensor <NUM> and consists of hardware <NUM> (typically a microcontroller equipped with a memory) and software <NUM>, the latter being stored in the memory of the microcontroller.

The balancing system also includes a stationary part with a processing and control electronics <NUM> that is supported by the frame <NUM> of the machine tool <NUM> and connected to a control unit <NUM> of the machine tool <NUM>.

A two-way contactless communication system <NUM> is provided between the rotating part and the stationary part of the balancing system, the communication system being suitable for establishing communication between the control system <NUM> and the processing and control electronics <NUM>, for transmitting analog and digital information. The communication system <NUM> is preferably of the optical type and comprises a first transceiver device <NUM> in the stationary part, coupled to the frame <NUM> of the machine tool <NUM>, and connected to the processing and control electronics <NUM> by means of an electric cable (not shown) and a second transceiver device <NUM> in the rotating part which faces the first transceiver device <NUM> and is connected to the control system <NUM> by means of a coiled electric cable which is housed in the axial opening <NUM>.

The communication system <NUM> is made in a known way, for example according to one of the alternatives described in the aforementioned patent application <CIT>, and is not illustrated in detail here.

The communication system <NUM> is used by the processing and control electronics <NUM> to send digital control signals to the control system <NUM> of the rotating part (for example for activating/deactivating the reading of the vibration sensor <NUM> or for driving the electric motors <NUM> which move the balancing masses <NUM>) and is used in the opposite direction by the control system <NUM> of the rotating part to send to the processing and control electronics <NUM> digital diagnostic signals and the reading, generally in analog form, of the vibration sensor <NUM>.

A wireless power transmission system is provided (generally integrated together with the communication system <NUM>) to provide the necessary power supply to the control system <NUM> of the rotating part. Generally, the power transmission system comprises an air-core transformer having the primary winding arranged in a component fixed to the frame <NUM> of the machine tool <NUM> (for example integrated in the first transceiver device <NUM>) and the secondary winding arranged in the rotating part connected to the spindle <NUM> (for example integrated in the second transceiver device <NUM>).

As illustrated in <FIG>, the software <NUM> of the control system <NUM> comprises a service application <NUM> and a management application <NUM>, both of them being configured to interface with the processing and control electronics <NUM> by means of the communication system <NUM> independently from each other. The service application <NUM> is configured to perform a limited number of tasks only when the rotating part, in particular the control system <NUM>, receives the power supply (i.e. it is turned on), while the management application <NUM> (which constitutes the firmware of the balancing head <NUM>) is configured to perform all the management of the balancing head <NUM> and of the associated vibration sensor <NUM> during the normal operation. In particular, when the control system <NUM> is powered, or receives the power supply after a suspension, or after a period of absence of power (that is when it is turned on), only the service application <NUM> automatically starts up and is configured to perform, according to the commands received from the processing and control electronics <NUM>, the necessary steps either to start the normal operation of the balancing system or to perform a software update. In particular, if the balancing system must normally operate then the service application <NUM> starts the management application <NUM> and stops until the next turning on. If, on the contrary, it is necessary to perform a software update, the service application <NUM> does not start the management application <NUM> and gets ready to receive (through the communication system <NUM>) code packets from the processing and control electronics <NUM> code. The service application <NUM> writes the code packets to the memory of the hardware <NUM> by overwriting the previous, existing version of the management application <NUM>, and the latter obviously cannot be started until the completion of the update. More specifically, when the update is completed, the service application <NUM> can stop after having started the management application <NUM>, or can turn off the control system <NUM>. During a mechanical working in which the grinding wheel <NUM> is in contact with a workpiece under processing or during the maintenance of the grinding wheel <NUM> in which the grinding wheel <NUM> is in contact with a dressing tool (dresser), the management application <NUM> of the software of the control system <NUM> uses the communication system <NUM> for continuously transmitting , preferably in analog form, a reading of the vibration sensor <NUM>. At the same time, the management application <NUM> cyclically reads the current value of one or more parameters of the rotating part by means of one or more sensors that are present in the rotating part, for example in the balancing head <NUM> and/or in the hardware <NUM> and/or in the second transceiver device <NUM> (for example one or more temperature sensors that detect the temperature of the rotating part) and checks whether the current value of the parameter (or parameters) is within a range of acceptable values. If the current value of at least one parameter (for example a temperature value of the rotating part) is significantly outside the corresponding range of acceptable values (for example if the detected temperature is too high) then the management application <NUM> stores in the memory of the hardware <NUM> the recording of the detected anomaly and interrupts the transmission of the reading of the vibration sensor <NUM>. When the reading of the vibration sensor <NUM> is interrupted, the processing and control electronics <NUM> generates an alarm and transmits it to the control unit <NUM> of the machine tool <NUM> which, on the basis of the provisions of a relative control program, can decide to immediately stop the operation in progress. In addition, the processing and control electronics <NUM> requests the control system <NUM> of the rotating part, more specifically the management application <NUM>, to restart the analog reading of the vibration sensor <NUM>. In response to this request from the processing and control electronics <NUM>, the management application <NUM> is programmed not to restart the analog reading of the vibration sensor <NUM> but to communicate in digital form the anomaly that has been just recorded and as a consequence of which the analog reading of the vibration sensor <NUM> was interrupted and then entrust the processing and control electronics <NUM> with the final decision on how to proceed.

What has been described so far refers to the preferred case in which the reading of the vibration sensor <NUM> is transmitted in analog form. If, on the other hand, the reading of the vibration sensor <NUM> is processed and digitized in the rotating part and is digitally transmitted to the processing and control electronics <NUM>, it is possible to associate this transmission with a digital signal that identifies the anomaly as soon as it is detected. In this case, therefore, the transmission of the reading of the vibration sensor <NUM> is not interrupted, and writing of recording of the anomaly to the memory of the hardware <NUM> is optional, recording which can still be useful for subsequent processing.

In the embodiment illustrated in the attached figures, the control system <NUM> of the rotating part comprises a single hardware <NUM> (i.e. a single microcontroller). According to other embodiments not shown, the control system <NUM> of the rotating part has a modular architecture, with a plurality of hardware <NUM>, typically two or three hardware <NUM> (i.e. two or three microcontrollers) physically separated and connected to one another for example by means of a BUS communication channel. In this case, all the hardware <NUM> of the control system <NUM> have a similar structure and are controlled by the same type of software <NUM> that is divided into a service application <NUM> and a management application <NUM> of its own.

In the embodiment shown in the attached figures the spindle <NUM> of the machine tool <NUM> supports a single grinding wheel <NUM>. According to another embodiment not illustrated, the spindle <NUM> of the machine tool <NUM> supports two grinding wheels <NUM> which are arranged at the two opposite ends of the spindle <NUM>.

In the embodiment illustrated in the attached figures the balancing system comprises a rotating part with a single balancing head <NUM>. while according to another embodiment, not illustrated, the rotating part of the balancing system comprises several balancing heads <NUM>. For example two balancing heads <NUM> can be arranged at the two opposite ends of the spindle <NUM> in embodiments comprising a single grinding wheel <NUM> or two distinct grinding wheels <NUM>.

As previously said, the balancing head <NUM> is equipped with two balancing masses <NUM>, for instance coplanar masses, which can rotate around the rotation axis <NUM> of the spindle <NUM>, so as to compensate for the unbalance present in the grinding wheel <NUM>. If it is sufficient to correct the unbalance in one plane only, one balancing head <NUM> is sufficient. In some cases it is necessary to correct the unbalance on both sides of the spindle <NUM>, therefore it is necessary to use two balancing heads <NUM>, suitably coordinated and arranged at opposite ends of the spindle <NUM>. The use of a single balancing head <NUM> entails the piloting of two balancing masses <NUM>, while the use of two balancing heads <NUM> entails the piloting of four balancing masses <NUM> (two for each balancing head <NUM>).

There are basically two strategies for balancing the grinding wheel <NUM>, a heuristic strategy and a deterministic strategy. The heuristic strategy is based on the execution of an action, the observation of the result, and the planning of the next action, until the unbalance is canceled, or the unbalance is reduced below a predetermined threshold value, the unbalance being detected by at least one specific vibration sensor (low frequencies), not shown in the figures, connected to the frame <NUM> of the machine tool <NUM> in a known way. If the action taken, e.g. a specific movement of the balancing masses <NUM>, goes in the direction of the reduction of the unbalance, it is proceeded in the same direction, otherwise a different action is developed. The deterministic strategy is based on the calculation of the unbalance vector and therefore of the position that the balancing masses <NUM> of the balancing head <NUM> (or balancing heads <NUM>) must take in order to cancel it. In order to implement this type of strategy, an accurate knowledge of the position, e.g. the angular position, of the balancing masses <NUM> of the balancing head <NUM> is required, which can be obtained by using appropriate position sensors or other devices, for example angular encoders.

If a heuristic strategy is used, position sensors or encoders in the balancing head <NUM> are not necessary, but "neutral position" sensors, or "home" sensors, capable of detecting when the balancing masses <NUM> of the balancing head <NUM> are in such a position to cause zero unbalance on the rotating part, are useful.

The two strategies can be mutually combined, for example in a balancing process including a first phase in which a deterministic type strategy is adopted for substantially reducing the unbalance, and a second refinement phase in which a heuristic type strategy allows to further reduce and substantially cancel the residual unbalance.

A control system <NUM> capable of driving more balancing heads <NUM>, e.g. two balancing heads, by adopting both possible strategies makes the system more flexible and easily adaptable to specific application needs.

There are two main way of driving the electric motors <NUM> which move the balancing masses <NUM> of a same balancing head <NUM> under the control of the control system <NUM> of the rotating part. More specifically, the two balancing masses <NUM> can be moved simultaneously or alternately, that is one at a time. If the application has a rotating part with two balancing heads <NUM> on the same spindle <NUM>, the same principle applies, that is the two balancing heads <NUM> can be simultaneously or alternately driven by the control system <NUM>. Depending on the combinations used, one or more balancing masses <NUM> can be simultaneously moved, from a minimum of one to a maximum of four.

An additional aspect of a balancing system according to the invention consists in the possibility of easily varying the bandwidth and the gain, which simplifies the configuration of the application program of the processing and control electronics <NUM> which processes the analog signal supplied by the vibration sensor <NUM> and increases its effectiveness.

A balancing system according to the present invention can be differently embodied with respect to what is schematically shown in the figures and described so far. The control system <NUM> can for example be partially or totally integrated in the second transceiver device <NUM> or be integral with it, connected to the balancing head <NUM> by means of the coiled electric cable. A different alternative consists in achieving the rotating part as an integral piece, that is in this case the second transceiver device <NUM>, the control system <NUM> and the balancing head <NUM> are parts of a single element or of elements rigidly connected to each other, and there is no coiled electric cable.

The rotating part of a balancing system according to the present invention that, as already mentioned above, can be achieved in a single piece, can also be arranged at one end of the spindle <NUM> instead of being housed in the axial opening <NUM> of the spindle <NUM>.

According to other embodiments of the present invention that are not illustrated, the spindle <NUM> of the machine tool <NUM> could mount a rotating tool different from the grinding wheel <NUM>.

The embodiments herein described can be combined with each other without departing from the scope of the present invention, which is defined by the appended claims.

The control method described above has a number of advantages.

First of all, the control method described above allows to update the software <NUM> of the control system <NUM> of the rotating part in a simple and quick way since the software <NUM> update is performed without any physical intervention by an operator to disassemble and reassemble mechanical parts and electrically connect and disconnect them using cables and proper connectors. In other words, the management application <NUM> (that is the firmware of the balancing head <NUM>) can be directly updated by the processing and control electronics <NUM> without requiring any physical interventions by the operator, more specifically interventions potentially complex and delicate interventions which inevitably and considerably slow down the process of update and consequently lengthen the period in which the machine tool does not have the possibility to operate. In this regard, it is important to note that the service application <NUM> does not require any type of update as it only performs two simple and quick tasks and therefore there is no real advantage in making the service application <NUM> faster and/or more efficient as it is largely sufficient that the service application <NUM> is effective, that is it is sufficient that it correctly performs the two above-mentioned tasks. Of course, in case of need the service application <NUM> can in any case be updated by disassembling the hardware <NUM> in order to physically connect the latter to an external computer.

Having diagnostic functions that are always active and therefore able to promptly communicate the occurrence of malfunctions or environmental phenomena that may damage the control system <NUM> of the rotating part - and, as a consequence, the spindle <NUM> and/or the grinding wheel <NUM> - increases the reliability of the application and of the machine tool <NUM>. Promptly knowing the occurrence of malfunctions or potential problems can prevent serious damage to the spindle <NUM> and/or the grinding wheel <NUM>. If there are environmental changes, such as for example an increase of the temperature inside the spindle <NUM>, which can cause damages to the system, a prompt transmission of this information to the processing and control electronics <NUM> allows the control unit <NUM> of the machine tool <NUM> to take actions in order to prevent damages.

Claim 1:
Balancing system for a rotating spindle (<NUM>) of a machine tool (<NUM>); the balancing system includes:
• a rotating part connected to the spindle (<NUM>) and comprising
• at least one balancing head (<NUM>) with
at least one balancing mass (<NUM>) which is eccentrically arranged with respect to a rotation axis (<NUM>), and
at least one electric motor (<NUM>) which is adapted to adjust the position of the balancing mass (<NUM>);
• at least one vibration sensor (<NUM>); and
• a control system (<NUM>) comprising at least one hardware (<NUM>) and at least one software (<NUM>) adapted to be executed by the hardware (<NUM>);
• a stationary part with processing and control electronics (<NUM>); and
• a two-way contactless communication system (<NUM>) which is adapted to establish a communication between the control system (<NUM>) and the processing and control electronics (<NUM>);
the balancing system is characterized in that the software (<NUM>) of the control system (<NUM>) comprises:
- a management application (<NUM>) that is configured to perform the whole management of the balancing head (<NUM>) and of the vibration sensor (<NUM>) during the normal operation; and
- a service application (<NUM>) that, when the control system (<NUM>) is powered after a suspension of the power supply, starts up automatically and is configured to either start the management application (<NUM>) or overwrite the existing version of the management application (<NUM>) with a new version of the management application (<NUM>).