JP4917079B2 - Ball screw mechanism deterioration inspection method - Google Patents

Description

  The present invention comprises a ball screw and a ball nut screwed to the ball screw via a plurality of balls, wherein the ball nut is filled with lubricating grease and sealed at both ends. The present invention relates to a deterioration inspection method for inspecting a deterioration state or a wear state of a ball screw mechanism and a ball screw mechanism.

  Machine tools, production machines, and the like driven by servo motors are provided with a plurality of ball screw mechanisms. As is well known, the ball screw mechanism is composed of a ball screw and a ball nut screwed into the ball screw via a plurality of balls. Therefore, when the rotation of the ball nut is restricted and the ball screw is driven to rotate, the ball nut is driven in the axial direction. For example, an electric injection molding machine is equipped with a mold clamping device that clamps a pair of molds, an injection device that injects a molten resin into the clamped molds, and the like. A mechanism is provided. In the case of a toggle type mold clamping device, a ball nut screwed into a ball screw is fixed to a cross head constituting a toggle mechanism. Therefore, when the ball screw is rotated by, for example, a servo motor, the cross head is driven in the axial direction, and the mold is opened and closed. The injection device includes a heating cylinder, a screw or the like provided inside the heating cylinder so as to be driven in the rotational direction and the axial direction, and an injection nozzle is provided in front of the heating cylinder. The rear end of such a screw is connected to a connecting plate via a predetermined mechanism, and a ball nut screwed with a ball screw is fixed to the connecting plate. Therefore, when the ball screw is driven to rotate, the screw is driven in the axial direction together with the connecting plate, and the molten resin in the heating cylinder is injected from the injection nozzle.

  Such a ball screw mechanism is lubricated by grease contained inside, but in the ball screw mechanism, the ball and the screw shaft rolling surface are in metal contact, and avoid wear and deterioration of each part due to rolling life. I can't. For example, if the grease is not properly replaced, the grease will deteriorate and lubrication will be insufficient, and the ball screw mechanism will wear or deteriorate early. However, even if the grease is periodically replaced and properly lubricated, it will gradually deteriorate due to wear and fatigue if it is operated for a long time. A ball screw mechanism that is properly lubricated is hardly deteriorated at an early stage, but as the operation time is accumulated, fine flaws start to occur on the ball surface. Furthermore, as the operating time accumulates, the deterioration progresses and the ball wears out, and the surface of the ball screw or ball nut peels off in a scale-like manner, causing loose peeling or flaking. Furthermore, if such a state is left unattended, a serious failure that damages the machine will occur, so it is necessary to estimate the deterioration state of the ball screw mechanism and perform maintenance or the like. Such signs of deterioration of the ball screw mechanism appear in the grease. For example, when fine scratches start to occur on the ball surface, a small amount of iron powder is contained in the grease, and the iron powder concentration in the grease increases as the deterioration progresses further. Therefore, if the concentration of iron powder in the grease is inspected, it is possible to infer the state of deterioration of the ball screw mechanism. Conventionally, grease is collected during regular inspections of the machine, and the iron powder concentration is measured with a predetermined inspection device. Or visually confirmed by skilled technicians. When the measured iron powder concentration in the grease exceeds a predetermined concentration, inspections are frequently performed, the grease is frequently replaced, and when the iron powder concentration is further increased, the ball screw mechanism is inspected. The parts are replaced as appropriate.

JP 2008-134136 A

  Although not a direct document of the present invention, Patent Document 1 describes a grease deterioration detection device that measures a deterioration state of grease sealed in a bearing. In the grease deterioration detection device described in Patent Document 1, a grease pocket having a predetermined capacity is provided in a bearing, and a sensor including a light emitting element and a light receiving element is provided in the grease pocket. Since the light emitted from the light emitting element is attenuated when passing through the grease, the concentration of iron powder in the grease can be obtained by a predetermined calculation by measuring the intensity of the light detected by the light receiving element. Thereby, it becomes possible to estimate the deterioration state of the grease.

  As in the past, it is possible to estimate the deterioration state of the ball screw mechanism by collecting grease and measuring the iron powder concentration during periodic inspections. However, there are problems to be solved, for example, a problem is found in the method of collecting grease. Conventionally known ball nuts do not have a sufficient seal, so grease is supplied from the specified greasing port in the ball nut and the enclosed grease leaks little by little. The grease will adhere to the exposed part of the ball screw. Therefore, the iron powder concentration can be measured by collecting grease adhering to the ball screw. However, since the grease adhering to the ball screw is scattered when the ball screw rotates at a high speed, it is difficult to collect a predetermined amount, and there is no guarantee that the grease is immediately after leakage. The iron powder concentration cannot be measured accurately. There is also a method for directly collecting the internal grease by disassembling the ball screw mechanism. In recent years, a ball screw mechanism has been developed that includes a ball screw having an improved thread groove shape and a ball nut having a seal that is in close contact with the screw groove and substantially prevents leakage of grease. A method of collecting grease by disassembling such a ball screw mechanism is also applicable. According to this method, the iron powder concentration in the grease can be accurately measured. However, the disassembly of the ball screw mechanism must be carried out with the machine stopped, so the work is complicated and requires a lot of man-hours, and cannot be carried out for a machine that is required to operate for 24 hours.

  If the grease deterioration detection device described in Patent Document 1 can be applied to the ball screw mechanism, the iron powder concentration in the grease can be accurately measured even when the ball screw mechanism is in operation, and the deterioration state of the ball screw mechanism is estimated. Can do. However, the grease deterioration detection device described in Patent Document 1 is a device provided in a large bearing such as a main shaft bearing of a wind turbine, and is provided with a grease pocket having a relatively large capacity so that a sensor can be installed therein. Is the premise. It is difficult to provide such a grease pocket in a ball screw mechanism provided in a production machine such as an electric injection molding machine.

  An object of the present invention is to provide a ball screw mechanism having a ball screw mechanism deterioration inspection method and a deterioration inspection device, which solves the above-described conventional problems or problems, and specifically, for inspection. It is not necessary to disassemble the ball screw mechanism, and it is not necessary to provide a special grease pocket in the ball screw mechanism, and it is possible to accurately measure the iron powder concentration in the grease even when the machine is in operation, and It aims at providing the ball screw mechanism provided with the deterioration inspection apparatus.

  In order to achieve the above object, the present invention forcibly discharges grease by leaving a predetermined amount of grease sealed in a ball nut after a predetermined period of time, and a new grease having substantially the same amount. Is configured to measure the iron powder concentration in the discharged grease and inspect the deterioration state of the ball screw mechanism.

Specifically, in order to achieve the above object, the invention according to claim 1 includes a ball screw and a ball nut screwed to the ball screw via a plurality of balls, and the ball nut is used for lubrication. In the ball screw mechanism in which the grease is sealed and the both ends thereof are sealed, the grease replacement performed when a predetermined operating time has passed is performed through the grease discharge hole reaching from the bottom to the inside of the ball nut. A fixed amount of grease is forcibly discharged by the piston pump so that more than 1/3 of the grease enclosed in the ball nut remains, and a new amount of grease substantially the same amount as the discharged grease is discharged. In this case, the iron powder concentration in the discharged grease is injected into the ball nut. Measure and configured to inspect the deterioration or wear state of the ball screw mechanism. The invention according to claim 2 is the degradation / wear state inspection method according to claim 1, wherein the piston pump is connected to a suction pipe connected to a lower portion of the ball nut, and the iron powder concentration Is measured such that the iron powder concentration in the grease in the suction pipe is measured by a magnetic balance type electromagnetic induction method, and the invention according to claim 3 is the deterioration / deterioration according to claim 1 or 2. In the wear state inspection method, when the ball screw mechanism is driven, the discharge of the grease, the injection, and the measurement of the iron powder concentration are performed.

The invention according to claim 4 comprises a ball screw and a ball nut screwed into the ball screw via a plurality of balls, and grease for lubrication is enclosed in the ball nut, In a sealed ball screw mechanism, a piston pump that discharges the grease enclosed in the ball nut, and new grease that is substantially the same as the amount discharged by the piston pump is injected into the ball nut. A fixed grease discharge valve and an iron powder concentration measuring means for measuring the iron powder concentration in the grease, and the piston pump is provided in a grease discharge hole opened to reach the inside of the ball nut from below. It is connected, after a lapse of a predetermined operating time, before so as to remain grease 1/3 or more within the ball nut Grease is quantitatively discharged by the piston pump, and substantially the same amount of grease is injected into the ball nut from the quantitative grease discharge valve, and the iron powder concentration measuring means is controlled by the piston pump. It is arranged to measure the iron powder concentration in the discharged grease. According to a fifth aspect of the present invention, in the ball screw mechanism according to the fourth aspect, the piston pump is connected to a suction pipe connected to a lower portion of the ball nut, and the iron powder concentration measuring means is a magnetic balance. The iron powder concentration meter is configured to measure the iron powder concentration by an electromagnetic induction method, and the iron powder concentration meter is configured to measure the iron powder concentration in the grease in the suction pipe. .

As described above, according to the present invention, a predetermined amount of grease is forcibly discharged from the lower portion of the ball nut by the piston pump so that 1/3 or more of the grease enclosed in the ball nut remains. When a new grease of substantially the same amount as the discharged grease is injected into the ball nut by the quantitative grease discharge valve , the iron powder concentration in the discharged grease is measured to determine the deterioration or wear state of the ball screw mechanism. Since the inspection is performed, the deterioration or wear state of the ball screw mechanism need not be disassembled and it is not necessary to dispose the ball screw mechanism and to install a special grease pocket in the ball nut. In addition, since the grease whose iron powder concentration is measured is guaranteed to be grease that has been enclosed in the ball nut until immediately before, the deterioration state of the ball screw mechanism can be accurately estimated. Further, since 1/3 or more of the grease remains when the grease is discharged, air is not involved in the discharged grease, and the iron powder concentration can be accurately measured. That is, since grease does not contain air, the volume of the grease to be measured is accurate, and the iron powder concentration can be accurately measured. Furthermore, when the grease is discharged, 1/3 or more of the grease in the ball nut remains, so even if the grease is measured and the iron powder concentration is measured, the minimum amount of grease is secured during that period. The ball screw mechanism can be operated without hindering lubrication. That is, even if continuous operation for 24 hours is required, the deterioration state of the ball screw mechanism can be inspected safely during operation. Further, according to another invention, since the iron powder concentration in the grease is configured to be measured by a magnetic balance type electromagnetic induction method, it is possible to accurately inspect the iron powder concentration in the grease, The deterioration state of the ball screw mechanism can be accurately estimated. According to another invention, the iron powder concentration measuring means is arranged to measure the iron powder concentration in the grease discharged from the grease discharging means, or the iron powder concentration meter is arranged in the grease in the suction pipe. Since the iron powder concentration is measured, a deterioration inspection device, that is, an iron powder concentration meter can be provided even in a narrow space. In addition, since the iron powder in the grease in the suction pipe is measured, only the iron powder in the grease can be accurately measured without mixing the iron powder in the atmosphere into the grease. .

  Embodiments of the present invention will be described below. The ball screw mechanism deterioration inspection apparatus 1 according to the present embodiment is provided on the side of the ball screw mechanism 2 having a predetermined structure in which the grease changing device 3 is provided. First, the ball screw mechanism 2 and the grease changing device 3 will be described. The ball screw mechanism 2 includes a ball screw 5 and a ball nut 6 screwed into the ball screw 5 via a plurality of balls. According to the embodiment shown in FIG. 1, the ball nut 6 is fixed to a predetermined member 7 and its rotation is restricted, and the ball screw 5 is driven to rotate and is reciprocally driven in the axial direction. It has become. At both ends of the ball nut 6, grease leakage prevention seals 9 and 9 having a structure that closely contacts the thread groove of the ball screw 5 are provided. The grease sealed inside the ball nut 6 by the seals 9 and 9 does not substantially leak outside. Further, although not shown in the drawing, a grease injection hole reaching the inside is formed in the upper part of the outer peripheral surface of the ball nut 6, and a grease supply port 10 for supplying grease from the outside is provided in the grease injection hole. ing. Similarly, although not shown in the drawing, a grease discharge hole reaching the inside is formed in the lower portion of the outer peripheral surface of the ball nut 6, and a discharge port 11 for discharging the grease to the outside is provided in the grease discharge hole. Yes.

  In general, the grease changing device 3 includes a discharge device 13 that forcibly sucks old grease sealed in the ball nut 6 and discharges it to the outside, and a supply device that supplies new grease to the ball nut 6. It comprises a grease device 14, a controller 15 that outputs commands to the discharge device 13 and the grease supply device 14. The discharge device 13 is connected to a suction pipe 17 that sucks grease from the discharge port 11, an air-driven piston pump 18 that is connected to the suction pipe 17 and forcibly sucks grease, and a discharge pipe 20 of the piston pump 18. It comprises a check valve 22 mounted. The piston pump 18 includes a cylinder 23 and a piston 24 that is provided in the cylinder 23 and driven by air. A check valve structure 25 is provided at the tip of the cylinder 23. An air-type piston cylinder unit that reciprocally drives the piston or piston rod 24, a pneumatic circuit that supplies / discharges compressed air to / from the piston cylinder unit, etc. are not shown in FIG. Since the piston pump 18 is configured as described above, when the piston 24 is pulled backward by a predetermined distance, the inside of the cylinder 23 becomes negative pressure, the valve of the check valve structure 25 is opened, and a predetermined amount of grease is formed. Is forcibly sucked into the cylinder 23 and the piston 24 is driven forward, the inside of the cylinder 23 is pressurized and the valve is closed, and the grease in the cylinder 23 is discharged from the discharge pipe 20.

  As is well known in the art, the greasing device 14 pressurizes and feeds new grease under pressure, a pressure feed pipe 28 connected to the discharge port of the grease pump 27, and a grease feed device 28 connected to the pressure feed pipe 28 to distribute the grease. , A plurality of conventionally known fixed-quantity grease discharge valves 31, 31,..., A fixed-quantity grease discharge valve 31 and a greasing port 10. And a greasing pipe 32 connected to each other. The grease pump 27 is maintained in a state in which new grease can be supplied, and the controller 15 is connected via a signal line 35 and is driven by a command from the controller 15.

  The ball screw mechanism deterioration inspection apparatus 1 according to the present embodiment includes an iron powder concentration meter 37 that measures the iron powder concentration by a so-called magnetic balance type electromagnetic induction method, and is provided in the suction pipe 17. In the magnetic balance type electromagnetic induction method, as is well known in the art, when a sample is placed in one of the pair of exciting coils having the same inductance and an alternating current is applied to both exciting coils, induction is induced. This is a method for measuring the amount of iron powder by utilizing a phenomenon in which a difference occurs in electric power. If such a voltage difference of the induced electromotive force is detected by a predetermined detection coil, the amount of iron powder contained in the sample can be accurately measured. Therefore, if the capacity of the grease to be measured is accurate, the iron powder concentration can be accurately measured. The suction pipe 17 is provided so as to penetrate one excitation coil of the pair of excitation coils provided in the iron powder concentration meter 37. As will be described later, air does not enter the suction pipe 17. The suction pipe 17 is filled with grease, and the capacity of the grease to be measured is constant, so that the iron powder concentration in the grease in the suction pipe 17 can be accurately measured. The suction pipe 17 is made of a resin pipe that transmits magnetic force, so that the concentration of iron powder in the grease inside the pipe can be accurately measured. The iron powder concentration meter 37 is connected to the controller 15 via a signal line 38 and is driven in conjunction with the grease changing device 3.

  The operation of the ball screw mechanism 2 according to the present embodiment will be described. The ball screw mechanism 2 is appropriately lubricated with grease 40 enclosed by 40 to 60% of the space inside the ball nut 6 as shown in a cross section in FIG. . When the machine has been operating for a predetermined time, for example several months, the grease is replaced. The controller 15 outputs a command to the piston pump 18. Then, the piston 24 is driven in the direction of the arrow Y1 by a set distance by an air cylinder (not shown) or the like. The inside of the cylinder 23 becomes negative pressure, the check valve structure valve 25 is opened, and the grease 40 inside the ball nut 6 is sucked into the cylinder 23 through the suction pipe 17. At this time, it is carried out so that at least 1/3 or more, preferably 1/2 or more of the amount of grease before suction remains in the ball nut 6. Since the suction is performed while leaving such an amount, almost no air is entrained in the grease sucked into the cylinder 23. Since the grease to be sucked does not contain air and the distance for pulling the piston 24 is constant, the amount of grease to be sucked is fixed. Next, the controller 15 outputs a command to the piston pump 18. Then, the piston 24 is driven in the direction of the arrow Y2, and the grease is discharged to the used grease reservoir 39 via the check valve 22. Grease 40 sucked from the ball nut 6 remains in the suction pipe 17.

  The controller 15 activates the grease pump 27. Then, the grease is pumped to the concentration block 30 via the pumping pipe 28. The grease distributed in the concentration block 30 is discharged from the fixed grease discharge valve 31. The discharge amount is a fixed amount and is substantially the same as the amount of grease discharged by the discharge device 13. The discharged grease is injected into the ball nut 6 through the greasing pipe 32 and the greasing port 10. This completes the grease replacement. It should be noted that since a plurality of fixed-quantity grease discharge valves 31, 31,... Are connected to the centralized block 30, other ball screw mechanisms not shown in the figure can be greased simultaneously.

The controller 15 outputs a command to the iron powder concentration meter 37. The suction pipe 17 is filled with grease 40 newly sucked from the ball nut 6. When the command is output, the iron powder concentration meter 37 measures the iron powder concentration in the grease in the suction pipe 17 by a magnetic balance electromagnetic induction method, and displays the iron powder concentration on a predetermined indicator or the like. Since the grease to be measured is the grease 40 enclosed in the ball nut 6 until just before, the deterioration state of the ball screw mechanism 2 can be accurately estimated. The deterioration state of the ball screw mechanism 2 can be estimated from the measured iron powder concentration, and can be handled as follows.
(1) When the iron powder concentration in the grease is 0.05% wt or less:
The ball screw mechanism 2 is in a normal state and has not deteriorated. Maintenance of the ball screw mechanism 2 is not necessary.
(2) When the iron powder concentration in the grease is 0.05 to 0.1% wt:
The ball surface of the ball screw mechanism 2 is scratched. The ball screw mechanism 2 is inspected as necessary.
(3) When the iron powder concentration in the grease is 0.1% wt or more:
The ball of the ball screw mechanism 2 is worn. There is a possibility that peeling or flaking has occurred in the ball screw 5 or the ball nut 6. The machine is stopped and the ball screw mechanism 2 is closely inspected to replace a deteriorated or worn part. Alternatively, the progress of deterioration of the ball screw mechanism 2 is monitored by performing grease replacement and measuring the iron powder concentration at a high frequency thereafter.

  Even after the grease is discharged from the ball nut 6, at least 1/3 or more of the grease remains in the ball nut 6, and the lubrication is performed quickly. There is no need to stop the machine. Therefore, grease replacement and iron powder concentration measurement can be performed even during operation. Since the grease is exchanged in a state where it remains 1/3 or more, preferably 1/2 or more, new grease and old grease are mixed. Accordingly, the grease immediately after the replacement also includes a predetermined iron powder, and the iron powder concentration measured at the next replacement of the grease includes such iron powder. . In other words, there is no guarantee that the measured iron powder concentration is the iron powder concentration caused by the iron powder generated between the previous grease replacement and the next grease replacement. There is a possibility that it cannot be estimated accurately. However, even if the old grease remains and is mixed with new grease, there is virtually no problem. That is, when the ball screw mechanism 2 is hardly deteriorated, since the old grease contains almost no iron powder, the measured iron powder concentration is low and there is no problem. Also, when the deterioration of the ball screw mechanism 2 starts, the progressing speed of the deterioration may be accelerated, but not decelerated. Therefore, the measured iron powder concentration becomes higher than the previous time, and when the previous grease is replaced. The amount of remaining iron powder can be ignored.

  The grease is discharged and lubricated so that the amount is substantially the same, and the grease is sealed so that the amount of grease enclosed in the ball nut 6 does not fluctuate. The amount may fluctuate, causing problems in lubrication. However, since the life of the ball screw mechanism is several years, even if the grease is replaced every several months, the number of grease replacements performed before replacing the ball screw is not large. Therefore, even if an error between the discharge amount and the lubrication amount is accumulated every time the grease is replaced, the variation in the amount of grease enclosed in the ball nut 6 is small and does not hinder the lubrication. .

  The deterioration inspection apparatus 1 for the ball screw mechanism 2 according to the embodiment of the present invention is not limited to the above embodiment and can be implemented in various forms. For example, the iron powder concentration meter 37 is described as an iron powder concentration meter that measures the iron powder concentration by a magnetic balance type electromagnetic induction method. The conductivity may be measured to estimate the iron powder concentration. Further, as described in Patent Document 1, a light emitting element and a light receiving element may be provided, and the iron powder concentration may be estimated from the attenuation amount of light transmitted through the grease. Furthermore, a special alarm device or the like may be provided to issue an alarm when the iron powder concentration measured by the iron powder concentration meter 37 exceeds a predetermined concentration. The grease changing device 3 can also be modified. For example, the grease changing device 3 is described so that a fixed amount of grease is discharged and a fixed amount of grease is supplied, but it may be a variable amount instead of a fixed amount and is substantially the same as the discharged grease. There is no problem if an amount of grease is supplied. Further, the new grease is supplied to the ball nut 6 from the upper part, but may be supplied from the lower part. In this case, a supply / discharge port can be shared by providing a switching valve.

It is a front view showing an embodiment of the invention typically.

Explanation of symbols

1 Ball screw mechanism deterioration inspection device 2 Ball screw mechanism 3 Grease changing device 5 Ball screw 6 Ball nut 9 Grease leakage prevention seal 10 Grease port
11 Discharge port 15 Controller 18 Piston pump 27 Grease pump 30 Centralized block 31 Metering grease discharge valve 37 Iron powder concentration meter

Claims (5)

In a ball screw mechanism comprising a ball screw and a ball nut screwed to the ball screw via a plurality of balls, lubrication grease is enclosed in the ball nut, and both ends thereof are sealed,
The grease replacement performed when a predetermined operating time has elapsed is to leave at least 1/3 of the grease enclosed in the ball nut from the grease discharge hole reaching from the bottom to the inside of the ball nut. A fixed amount of grease is forcibly discharged by the piston pump, and a new grease substantially equal to the discharged grease is injected into the ball nut by the fixed amount grease discharge valve,
At this time, a deterioration / wear state inspection method for the ball screw mechanism, wherein the iron screw concentration in the discharged grease is measured to inspect the deterioration or wear state of the ball screw mechanism. 2. The deterioration / wear state inspection method according to claim 1, wherein the piston pump is connected to a suction pipe connected to a lower portion of the ball nut, and the measurement of the iron powder concentration is performed in the suction pipe. A method for inspecting the deterioration and wear state of a ball screw mechanism, wherein the concentration of iron powder in grease is measured by a magnetic balance type electromagnetic induction method. The deterioration / wear state inspection method according to claim 1 or 2, wherein when the ball screw mechanism is driven, the discharge of the grease, the injection, and the measurement of the iron powder concentration are performed. Degradation and wear state inspection method for ball screw mechanism. In a ball screw mechanism comprising a ball screw and a ball nut screwed to the ball screw via a plurality of balls, lubrication grease is enclosed in the ball nut, and both ends thereof are sealed,
A piston pump that discharges the grease enclosed in the ball nut, a quantitative grease discharge valve that injects a new amount of grease substantially equal to the amount discharged by the piston pump into the ball nut, and grease An iron powder concentration measuring means for measuring the iron powder concentration in the inside,
The piston pump is connected to a grease discharge hole opened to reach the inside from the lower part of the ball nut,
When a predetermined operating time has elapsed, the grease is quantitatively discharged by the piston pump so that grease remains in the ball nut, and substantially the same amount of grease is discharged from the quantitative grease discharge valve. It is designed to be injected into the ball nut,
The ball screw mechanism, wherein the iron powder concentration measuring means is arranged to measure an iron powder concentration in grease discharged by the piston pump. In the ball screw mechanism according to claim 4, wherein the piston pump is connected to a suction pipe connected to the lower portion of the ball nut, the said iron powder concentration measuring means iron powder density by the magnetic balance type electromagnetic induction method It consists of an iron powder densitometer that is designed to measure,
The ball screw mechanism, wherein the iron powder concentration meter is configured to measure an iron powder concentration in grease in the suction pipe.

Images