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Title:
METHOD AND DEVICE FOR CREATING A STREAM OF AIR FOR REMOVING RESIDUE PARTICLES FORMED IN CONNECTION WITH CUTTING, GRINDING AND/OR POLISHING OF A STONE OR STONE-LIKE MATERIAL
Document Type and Number:
WIPO Patent Application WO/2009/041888
Kind Code:
A1
Abstract:
A method for creating a stream of air for removing residue particles formed in connection with cutting, grinding and/or polishing of a stone or stone-like material is disclosed. The method comprising energizing an electric motor (27) to drive an impeller (26) to create the stream of air, the electric motor being energized by an alternating current (Id); and setting a frequency (fd) of said alternating current in response to a desired current value of the alternating current. There is also disclosed a device adapted to carry out the method. The method allows for a stream of air that is efficient in removing particles of the above kind and origin, and which creation is virtually independent on the available mains power. A large air flow can be provided during normal operation and a large underpressure can be provided for filter cleaning maintenance.

Inventors:
SUNESSON, Johan (Drottninggatan 48, S- Linköping, SE-582 27, SE)
Application Number:
SE2008/051032
Publication Date:
April 02, 2009
Filing Date:
September 15, 2008
Export Citation:
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Assignee:
HTC SWEDEN AB (Box 69, Söderköping, S-614 22, SE)
SUNESSON, Johan (Drottninggatan 48, S- Linköping, SE-582 27, SE)
International Classes:
B24B7/18; A47L9/16; A47L9/28; B04C11/00; B24B55/10; H02P7/00
Domestic Patent References:
WO2003076131A1
Foreign References:
DE202005001746U1
DE3710619A1
DE3718263A1
EP1808234A1
Attorney, Agent or Firm:
IPENDO AB (Södergatan 15, S- Malmö, SE-211 34, SE)
Download PDF:
Claims:

CLAIMS

1. A method for creating a stream of air for removing residue particles formed in connection with cutting, grinding and/or polishing of a stone or stone-like material, the method comprising:

- energizing an electric motor (27) to drive an impeller (26) to create the stream of air, the electric motor being energized by an alternating current (l d ); and - setting a frequency (f d ) of said alternating current in response to a desired current value of the alternating current.

2. The method according to claim 1 , further comprising, during an operative period, - selecting the desired current value to be a value in a range from about 50% to about 150% of a rated current value (I R ) of the motor.

3. The method according to claim 2, further comprising, during a maintenance subperiod of the operative period, - equalizing an underpressure in the device when the frequency (fd) of the alternating current has reached a target value (fMAiNτ)-

4. The method according to claim 3, wherein the target value is less than any frequency (f d ) of the alternating current during normal operation, such as less than a determined target frequency (fNORivi), typically about 30% or less of the target frequency ^NORM)-

5. The method according to any one of claims 3-4, further comprising,

- obstructing the stream of air to form the underpressure.

6. The method according to claim 5, wherein the stream of air is obstructed by blocking of an air stream inlet (12).

7. The method according to any one of the preceding claims, further comprising, during a start and/or stop period,

- varying a desired frequency value; and

- repeatedly setting the frequency (f d ) of the alternating current in response to the desired frequency value in such way that the frequency (f d ) of the alternating current changes and reaches a target value

(flMORIVl)-

8. The method according to claim 7, wherein the frequency (f d ) of the alternating current changes substantially linearly in the start and/or stop period.

9. The method according to any one of claims 7-8, wherein the startup and/or stop period is at least 2 s.

10. A device for creating a stream of air adapted to remove residue particles formed in connection with cutting, grinding and/or polishing of a stone or stone-like material, the device comprising:

- means (30) for energizing an electric motor (27) to drive an impeller (26) to create the stream of air, the electric motor being energized by an alternating current (l d ); and

- means (30) for setting a frequency (f d ) of said alternating current in response to a desired current value of the alternating current.

1 1. The device according to claim 10, further comprising means (30) for selecting, during an operative period, the desired current value to be a value in a range from about 50% to about 150% of a rated current value (I R ) of the motor.

12. The device according to claim 1 1 , further comprising means (23) for equalizing an underpressure in the device when the frequency (f d ) of the alternating current has reached a target value (fιviAiNτ)-

13. The device according to claim 12, wherein the target value is less than any normal operation frequency (fd) of the alternating current, such as less than a determined target frequency (fiMORM), typically about 30% or less of the target frequency (fNORM)-

14. The device according to any one of claims 12-13, further comprising means for obstructing the stream of air to form the underpressure.

15. The device according to claim 14, wherein the means for obstructing the stream of air is adapted to block an air stream inlet (12).

16. The device according to any one of claims 10-15, further comprising, means (30) for varying a desired frequency value during a start and/or stop period; and means (30) for repeatedly setting the frequency (fd) of the alternating current in response to the desired frequency value being varied in such way that the frequency (f d ) of the alternating current changes and reaches a target value ^NORM)-

17. The device according to claim 16, wherein the means (30) for varying the desired current is arranged to change the frequency (fd) of the alternating current substantially linearly in the start and/or stop period.

18. The device according to any one of claims 16-17, wherein the start and/or stop period is at least 2 s.

Description:

METHOD AND DEVICE FOR CREATING A STREAM OF AIR FOR

REMOVING RESIDUE PARTICLES FORMED IN CONNECTION WITH

CUTTING, GRINDING AND/OR POLISHING OF A STONE OR STONE-LIKE

MATERIAL

Technical field

The present disclosure relates to a method for creating a stream of air for removing residue particles formed in connection with cutting, grinding and/or polishing of a stone or stone-like material. It also related to a device adapted to carry out the method.

Background

A grinding machine for grinding and polishing of large area stone or stone-like floors, such as concrete floors, produces residue particles, e.g. in the form of dust and debris, which have to be removed. Information on a currently predominant type of grinding machine can e.g. be found in WO03076131.

For process efficiency, it is desirable to be able to remove the residue particles in connection with the grinding and as efficiently as possible. This is also important from a health perspective since the grinding typically is being performed indoor under human supervision and/or in environments where people usually are present.

A grinding machine of this kind produces a large amount of residue particles, e.g. as much as 1000 kg/hour. Additionally, even for efficient grinding machines, it typically takes many hours to process a large area floor, and it is thus both a large amount of residue particles that has to be removed per time unit, as well as a large total amount. Also, owing to the type of material being processed, the residue particles are, as such, comparatively hard to collect in an effective manner.

The grinding and the residue removal should preferably be executed with as little downtime, and with as little need for user intervention, as possible.

One solution, especially in case of dry grinding, is to use a vacuum cleaner for removing the residue particles. However, because of the peculiarities pertaining to this kind of floor grinding, many conventional vacuum cleaner solutions for industrial purposes cannot be used or does not perform as well as would be desirable.

In one known solution for removing residue particles from the above mentioned type of grinding of concrete and stone-like floors, a vacuum cleaner with a cyclone pre-separator is used. A stream of air for bringing residue particles is generated by an impeller driven by an induction electric motor (5.5 kW, 16 A) adapted to be supplied directly by a mains power outlet providing three-phase alternating current (3x400 W, 50 Hz). To reduce current surge and losses when starting/stopping the impeller, a star/delta- starter is used at start and stop.

Summary

In view of the above, an object of this disclosure is to present a solution overcoming or at least alleviating problems in the prior art. A more specific object is to provide an improved or alternative method and device for creating a stream of air removing residue particles formed in connection with cutting, grinding and/or polishing of a stone or stone-like material.

Hence, according to one aspect, the above mentioned and other objects that will be evident from the following description, are achieved by a method for creating a stream of air for removing residue particles formed in connection with cutting, grinding and/or polishing of a stone or stone-like material, the method comprising: energizing an electric motor to drive an impeller to create the stream of air, the electric motor being energized by an alternating current; and setting a frequency of said alternating current in response to a desired current value of the alternating current.

The method allows for a stream of air that is efficient in removing particles of the above kind and origin, and which creation is virtually independent on the available mains power. A large air flow can be provided during normal operation and a large underpressure can be provided for filter cleaning maintenance. The method also allows for efficient implementation

and integration of functions relating to the creation of the stream of air and to the removal of the particles, including maintenance and filter cleaning operations.

The method may further comprise selecting, during an operative period, the desired current value to be a value in a range from about 50% to about 150% of a rated current value of the motor.

Selecting the desired current value to substantially be, or be close to the rated current value, allows for efficient utilization of the electric motor and thereby for creation of a stream of air that is as efficient as possible during different operative situations and at different loads.

The method may further comprise, during a maintenance subpehod of the operative period, equalizing an underpressure in the device when the frequency of the alternating current has reached a target value.

The target value may be less than any frequency of the alternating current during normal operation, such as less than a predetermined target frequency, typically about 30% or less of the target frequency.

By normal operation is here meant any situation where new particles are being, or at least are allowed to be, contained in the stream of air.

The method may further comprise obstructing the stream of air to form the underpressure.

The stream of air may be obstructed by blocking of an air stream inlet. Thus, the air stream inlet may be blocked upstream of its connection to the cyclone.

The method may further comprise varying, during a start and/or stop period, the desired current value; and repeatedly setting the frequency and a voltage of the alternating current in response to the desired current value being varied in such way that the alternating current energizing the electric motor changes and reaches a target value.

One advantage here is that the current surge and losses during start/stop can be controlled and the stream of air can be created/stopped in a nice and smooth manner.

The alternating current may change substantially linearly in the start and/or stop period. The startup and/or stop period may be at least 2 s.

According to another aspect thre is provided a device for creating a stream of air adapted to remove residue particles formed in connection with cutting, grinding and/or polishing of a stone or stone-like material, the device comprising means for energizing an electric motor to drive an impeller to create the stream of air, the electric motor being energized by an alternating current; and means for setting a frequency of said alternating current in response to a desired current value of the alternating current.

The device may further comprise means for selecting, during an operative period, the desired current value to be a value in a range from about 50% to about 150% of a rated current value of the motor.

Moreover, the device may further comprise means for equalizing an underpressure in the device when the frequency of the alternating current has reached a target value. The target value may be less than any normal operation frequency of the alternating current, such as less than a predetermined target frequency, typically about 30% or less of the target frequency.

The device may further comprise means for blocking the stream of air to form the underpressure. The means for obstructing the stream of air may be adapted to block an air stream inlet. The device may further comprise means for varying a desired frequency value during a start and/or stop period; and means for repeatedly setting the frequency of the alternating current in response to the desired frequency value being varied in such way that the frequency of the alternating current changes and reaches a target value. The means for varying the desired current may be arranged to change the frequency of the alternating current substantially linearly in the start and/or stop period. The start and/or stop period may be at least 2 s.

Brief Description of the Drawings The above as well as other aspects, objects, features and advantages of the present solution, will be better understood through the following illustrative and non-limiting detailed description, with reference to the appended drawings.

In all figures, the dimensions as sketched are for illustration only and do not reflect the true dimensions or ratios. All figures are schematic and not to scale.

Fig. 1 a schematically shows a side view of a device according to an embodiment.

Fig. 1 b schematically shows a cross-sectional top view of a part of the device shown in Fig. 1 a.

Fig. 2 is a flow chart schematically illustrating a method according to an embodiment. Fig. 3 schematically exemplifies a frequency of an alternating current resulting from the method according to the embodiment.

Description of Embodiments

Fig. 1 a schematically shows a side view of a device according to an embodiment, the device comprising an air stream generator 20, a separator unit 10 having a housing 1 1 , and a controller 30. Inside the separator unit 10 there is arranged a cone shaped pre-separator 15 of cyclone type with its narrow end facing downward. The separator unit 10 has at its upper part an air stream inlet 12 to which a suction hose (not shown) is connectable. The inlet 12 of the separator unit is connected to an inlet 13 of the pre-separator 15. At an upper part of the pre-separator there is a pre-separator outlet 16 which exits into a space between the pre-separator and the housing 1 1 of the separator unit 10. A filter 9 is arranged between the outside of the pre- separator 15 and the wall of the housing 1 1 in such way that there is a passage between the pre-separator 15 and the filter 9, and between the filter 9 and the inner wall of the housing 1 1. The separator unit 10 is further provided with an air stream outlet 14 in the housing 1 1 , which air stream outlet 14 is connected to an inlet 21 of the air stream generator 20. The air stream generator comprises an impeller 26, an electric motor 27 arranged to drive the impeller 26, an upstream cavity 22 located at a suction side of the impeller 26 and a downstream cavity 24 located at a blow side of the impeller 26. The upstream cavity is provided with a pressure equalizing controllable

intake 23, such as an opening provided with a controllable air tight valve, shutter or the like.

Still referring to Fig. 1 a, the electric motor, such as an induction motor, is powered by alternating current, preferably 3-phase, provided by a controller 30 arranged to control the motor and the controllable air seal 23.

Fig. 1 b schematically shows a top view cross section of the separator unit in Fig. 1 a. In the shown example the separator has a substantially symmetric, here circle-shaped, cross-section, with the filter 9 enclosing the cyclone pre-separator 15 in the cross-section. Basic function of the device in Fig. 1 will now be described. When the motor 27 is energized it drives the impeller 26 which then moves air from the upstream cavity 22 to the downstream cavity 24 from where it is directed out from the air stream generator via outlet 25. As a result air will start to stream into the upstream cavity 22 from the separator unit 10 via inlet 21. When the air is leaving the separator unit 10 via outlet 14 there is created a stream of air being sucked into the cyclone pre-separator 15 via inlet 12. The created air stream entering via inlet 12 contains residue particles from grinding and/or polishing of a stone or stone-like material and should preferably, during as many different operative situations as possible be as effective as possible to carry such particles, thereby removing them from the floor being processed and the surroundings. The interior design of the separator unit 10 determines how the air stream flows from the inlet 12 to the outlet 14 and how particles are separated from the air stream along the way. The larger arrows in Fig. 1 schematically, and in a simplified manner, show the main path of the airflow in the device. In the cyclone pre-separator 15 air entering via inlet 13 circulates towards the narrow end along the inner walls until the narrowing causes the stream of air to change direction and to circulate back in the center towards and out via the pre-separator outlet 16. Particles, and in particular larger ones, fall out from the stream of air in the pre-separator and can be collected at the bottom. After leaving the pre-separator 15 the air flows through the filter 9 towards the separator unit outlet 14 and into the air stream generator inlet 21. The particles remaining in the stream at this point, i.e. particles that have not been removed by the cyclone pre-separator or the filter 9, may be

removed by a filter (not shown) for fine particles, such as a high efficiency particle air filter (HEPA filter), which may be arranged in the air stream generator, or elsewhere, in such way that the air has to pass through it before being allowed to escape back to an outer environment. Fig. 2 is a flow chart schematically illustrating a method according to an embodiment, the method being adapted to operate the separator unit 10 and air stream generator 20. In a step 101 it is decided if there is a start/stop period or not, i.e. whether the impeller is to be started or stopped, or continue creating the stream of air (in cases the impeller is already running). Start/stop periods are typically user initiated. During a start or stop period the motor driving the impeller will change from/to being provided with no alternating current, to/from being provided with an alternating current for creating the stream of air removing the residue particles. In the case of a start or stop period, in a step 107, a desired frequency value is being selected, then, in a step 109, frequency f d of the alternating current energizing the electric motor is set in response to the selected desired value. In a step 1 11 it is checked whether the frequency fd corresponds to a target frequency value or not. The target value corresponds to the desirable frequency at the end of the start or stop period, i.e. 0 Hz in the case of a stop period and the frequency desirable to operate the motor 27 at the case of a start period. It is typically desirable to increase/decrease the frequency continuously and comparatively slowly during start/stop. Hence, as long as the target frequency has not been reached, a number of different subsequent desired frequency values are typically being selected with the frequency set accordingly. When the target value has been reached, the corresponding start/stop period ends. Typically the length of a start and/or stop period is predetermined and typically a sequence of desired frequency values have been pre-selected or predetermined so that the frequencies being set during start and/or stop correspond to a predetermined frequency vs. time relationship. Typically, but not necessary, the relationship is linear, e.g. so that the frequency increases linearly from 0 Hz to the target value during a predetermined start period, such as during 15 s. The voltage U d being provided to the motor during start typically corresponds to a rated voltage value (U R ) of the motor, at least

during a latter part of the start period. The voltage U d may be lower at a first part of the start period.

Since the start/stop periods typically are user initiated, a stop period may for example directly be followed, or interrupted, by a start period. It should be noted that since the current after completion of a stop period typically is 0 Hz, there is normally no need for further action until the next start period is initiated. After a stop period thus normally follows an idle state in step 101 , although this is not explicitly shown in the flow chart in Fig. 2 where start/stop handling are presented together. Still referring to the flow chart of Fig 2, after a start period normally an operative period follows, i.e. a period during which the stream of air is removing residue particles from and during the cutting, grinding and/or polishing of stone or stone-like floors. In a step 103 a desired current value for the operative period is selected. This desired current value is typically the same, i.e. kept constant, during the whole period of operation and is preferably selected to correspond to the rated current value of the electric motor 257. In a next step 105 the frequency fd of the alternating current provided to the electric motor is set in response to the desired value, i.e. so that the current l d will, or at least strive to, correspond to the desired value. During the operative period the voltage Ud being provided to the motor typically corresponds to the rated voltage value (U R ) of the motor. Anyhow, in practice there will typically be some fluctuations in the U d level when the frequency is varied. During normal load, for example during a period when there is low or normal amount of particles being removed, or no fluctuation of the air stream during higher load, such as when a substantially constant amount of the same type and size of particles are being removed with insignificant clogging of filters etc., the frequency f d is typically being set to the same value in response to the desired current value. However, when the load increases or decreases from/to normal load, or changes at higher load, the frequency f d varies and is set to different values, although the desired current value which the frequency f d is set in response to is the same.

Moreover, still referring to the flow chart of Fig 2, during the operative period a subpehod of maintenance may occur. Such period may be user

initiated, or may be initiated automatically when a certain condition or conditions are fulfilled, for example when there is a certain degree of filter clogging, after a determined period of time etc. When maintenance occurs the separator air inlet may be blocked on purpose in a step 1 15. The blocking may be performed manually or automatically. In one embodiment blocking of the separator air inlet is what initiates a maintenance period. Blocking of the air inlet means increasing the load since air is pumped out of the system through outlet but no air is allowed to flow in. An underpressure is hence building up in the separator unit 20 and the upstream cavity 22. Although the load increases during maintenance, the desired current value is the same as during normal operation, i.e. preferably the rated current value of the motor. When the load increases, the frequency f d will eventually decrease. In a step 1 17 it is checked if a determined frequency has been reached, which typically is a frequency lower than any frequency that can be expected during normal operation and load. For example, normal operation may be performed at about 75 Hz and the determined frequency may be 45 Hz. The determined frequency corresponds to a certain underpressure in the upstream cavity and may be predetermined by routine experimentation to correspond to a desirable underpressure. When the determined frequency has been reached during the maintenance subperiod, the underpressure is equalized. This is preferably accomplished by that the controller sends a control signal, such as a voltage signal, to the pressure equalizing controllable intake 9, which in response opens up fully and instantly. As a result there will be sudden air wave sent "backwards" through the filter 9, which by the direction and impact of the air wave will be cleaned of particles clogging the filter. The particles fall to the bottom of the separator unit 20 where they may be collected and later removed. After the pressure has been equalized in step 1 19, the maintenance period is typically over, the blocking of the air inlet 12 is removed in a step 121 and normal operation may continue. Fig. 3 schematically exemplifies a drive frequency f d of an alternating current provided to the electric motor during a start, operative, maintenance and stop period respectively, using the method as described above. During the start/stop periods the frequency fd is being changed, here linearly ramped,

from/to 0 Hz to/from the target value at normal operation f N oRM- The maintenance subperiod is typically comparatively short, such as less than 10 s and is typically determined by how fast a desirable underpressure can be built up after the inlet 12 has been blocked. The target frequency ϊ MAINT reached at the end of the maintenance period is typically, but not necessary, significantly lower than the normal frequency, and typically selected lower than the lowest frequency that may be set during high load without there being total block of the air stream. The duration of the operative period is typically determined by the user. One advantage of the method presented in the foregoing is that the start/stop, maintenance and normal modes of operation are compatible and allows for implementation by a single device, the controller in Fig. 1 , which e.g. may be a combined programmable logic device and frequency converter/ variable frequency drive. Such devices, which are commercially available, can be programmed to execute the method and be connected between a power mains and the electric motor of the air stream generator. Corresponding functionality provided by such devices may alternatively be integrated as part of or in the same device as the air stream generator. As is realized by the skilled person, the method described herein may be performed also by other distributed or integrated components.

With reference to Fig. 1 , in one detailed example, a 3-phase induction motor rated 7.1 A, 3 kW, 400 V was used as the electric motor 27. As the controller 30 a combined PLD/programmable frequency converter was used and programmed to execute the above described method. The converter was connected between the electric motor and a power mains (50 Hz, 3 * 400 V) and it was thus arranged to convert the mains alternating current to a new alternating current energizing the motor. The controller 30 was programmed to, during start/stop periods, under a period of 15 s linearly ramp the frequency to/from a operative target value of 75 Hz from/to 0 Hz. The controller was programmed with the rated values of the motor and to, during the operative period, provide at most the rated current value to the motor. In the operative period, with virtually no particles being removed by the created air stream, the motor became energized at 75 Hz at an alternating current of

about 2 A. In the operative period, with a moderate amount of concrete residue particles being removed, corresponding to a normal operative situation, the motor became energized at 75 Hz at an alternating current at about 6.5 A. During operation, maintenance subpehods was user initiated by manually blocking the air stream inlet corresponding to 23 of the device. The controller was programmed to, when the frequency reached 45 Hz, send a 24 V signal to an electro-magnet based air tight valve of the upstream cavity 22, corresponding to the pressure equalizing controllable intake 23. Upon receipt of the signal the valve opened up instantly, pressure was equalized, and then the valve was closed. This pressure equalizing was performed in about 5 s. The blocking of the inlet was then removed and normal operation continued. During the blocking and when the frequency reached 45 Hz, the alternating current provided to the motor corresponded to the rated current value (7.1 A).




 
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