Gas concentration meter, control method of gas concentration meter, lamination molding apparatus, and control method of oxygen concentration meter for lamination molding apparatus

A gas concentration meter includes a first gas concentration detection sensor capable of detecting at least a gas concentration in a first concentration range, a second gas concentration detection sensor capable of detecting at least a gas concentration in a second concentration range, and a control unit. An upper limit value of the second concentration range is lower than an upper limit value of the first concentration range, and a lower limit value of the second concentration range is lower than a lower limit value of the first concentration range. The control unit is configured to output either the lower limit value of the first concentration range or the upper limit value of the second concentration range as an indication value when an output signal of the first gas concentration detection sensor corresponds to a gas concentration lower than the lower limit value of the first concentration range.

FIELD

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2019-096759, filed May 23, 2019. The contents of this application are incorporated herein by reference in their entirety. The present disclosure relates to a gas concentration meter and a control method thereof, a lamination molding apparatus and a control method thereof for a lamination molding apparatus.

BACKGROUND

In lamination molding of metal, a material layer made of a metal material is formed, and a beam such as a laser beam or an electron beam irradiates onto a predetermined portion of the material layer to sinter or melt the irradiated material layer to form a solidified layer. Then, a desired three-dimensional molded object is formed by repeating the formation of the material layer and the formation of the solidified layer.

In recent years, the capacity of the lamination molding apparatus for performing lamination molding of such a metal has been improved. With the improvement of the capacity, the applicable range of the lamination molding apparatus of which main purpose is to produce a prototype has been increasing. Particularly in recent years, the opportunity to manufacture important parts and the like by using the lamination molding apparatus has been increasing even in the medical field and the aerospace field. Since parts and the like used in these fields are required to be higher in quality than components used in other fields, it is necessary to perform molding under a low oxygen concentration environment depending on the type thereof.

Furthermore, when molding is performed in an environment with a low oxygen concentration, it is necessary to monitor whether or not the environment can be maintained during the formation.

Therefore, it is necessary to constantly or periodically measure the oxygen concentration in the molding chamber (chamber) in which lamination molding is performed. However, unless a plurality of sensors is used, the oxygen concentration in the molding chamber may not be measured.

It should be noted that in a concentration meter using a plurality of sensors, for instance, as described in Japanese Patent No. 3658285, switching from one sensor to another sensor is performed at a predetermined concentration, and the switching criterion is differed between when the concentration increases and decreases.

SUMMARY

Yet, there are various sensors for detecting the gas concentration, but a sensor having a desired performance may not necessarily be required in consideration of a use environment such as a temperature, performance such as a measurable range and a resolution, a price, and the like. As in the technology described in Japanese Patent No. 3658285, it may be difficult to provide a margin for switching criteria of a plurality of sensors.

Further, since various sensors generally have a detection error, it is more difficult to provide a margin for switching criteria of a plurality of sensors in consideration of the error.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a gas concentration meter, a control method of gas concentration meter, a lamination molding apparatus and a control method of oxygen concentration meter for a lamination molding apparatus in which a detection range is not missed even when a plurality of sensors are used.

According to the present invention, there is provided a gas concentration of a specific gas in a chamber, comprising: a first gas concentration detection sensor configured to detect at least the gas concentration in a first concentration range; a second gas concentration detection sensor configured to detect at least the gas concentration in a second concentration range, wherein an upper limit value of the second concentration range is lower than an upper limit value of the first concentration range, and a lower limit value of the second concentration range is lower than a lower limit value of the first concentration range; a control unit configured to: output an indication value based on an output signal of the first gas concentration detection sensor when an output signal of the first gas concentration detection sensor indicates a gas concentration in the first concentration range and an output signal of the second gas concentration detection sensor indicates a gas concentration higher than the upper limit value of the second concentration range, output an indication value based on an output signal of the second gas concentration detection sensor when an output signal of the second gas concentration detection sensor indicates a gas concentration in the second concentration range and an output signal of the first gas concentration detection sensor indicates a gas concentration lower than the lower limit value of the first concentration range, output an indication value based on an output signal of either the first gas concentration detection sensor or the second gas concentration detection sensor when an output signal of the first gas concentration detection sensor indicates a gas concentration in the first concentration range and an output signal of the second gas concentration detection sensor indicates a gas concentration in the second concentration range, and output either the lower limit value of the first concentration range or the upper limit value of the second concentration range as an indication value when an output signal of the first gas concentration detection sensor indicates a gas concentration lower than the lower limit value of the first concentration range and an output signal of the second gas concentration detection sensor indicates a gas concentration higher than the upper limit value of the second concentration range; and an indication value display unit configured to display the indication value output from the control unit; wherein the first and second gas concentration detection sensors, and the indication value display unit are connected to the control unit.

According to the present invention, there is provided a lamination molding apparatus to form a molded object, comprising: a chamber configured to cover a molding region in which a desired three-dimensional molded object is formed; an inert gas supply device configured to fill the chamber with an inert gas; and an oxygen concentration meter configured to detect an oxygen concentration in the chamber, wherein the oxygen concentration meter comprises: a first oxygen concentration detection sensor configured to detect at least the oxygen concentration in a first concentration range, a second oxygen concentration detection sensor configured to detect at least the oxygen concentration in a second concentration range, wherein an upper limit value of the second concentration range is lower than an upper limit value of the first concentration range, and a lower limit value of the second concentration range is lower than a lower limit value of the first concentration range, a control unit, when the supply of the inert gas in the chamber is started by the inert gas supply device, configured to: output an indication value based on an output signal of the first oxygen concentration detection sensor when an output signal of the first oxygen concentration detection sensor indicates an oxygen concentration in the first concentration range, output an indication value based on an output signal of the second oxygen concentration detection sensor when an output signal of the second oxygen concentration detection sensor indicates an oxygen concentration in the second concentration range and an output signal of the first oxygen concentration detection sensor indicates an oxygen concentration lower than the lower limit value of the first concentration range, and output either the lower limit value of the first concentration range or the upper limit value of the second concentration range as an indication value for a predetermined time when an output signal of the first oxygen concentration detection sensor indicates an oxygen concentration lower than the lower limit value of the first concentration range and an output signal of the second oxygen concentration detection sensor indicates an oxygen concentration higher than the upper limit value of the second concentration range, and an indication value display unit configured to display the indication value output from the control unit; wherein the first and second oxygen concentration detection sensors, and the indication value display unit are connected to the control unit.

According to the present invention, there is provided a control method of a gas concentration meter for detecting a gas concentration of a specific gas in a chamber, comprising steps of: detecting at least the gas concentration in a first concentration range by a first gas concentration detection sensor; detecting at least the gas concentration in a second concentration range by a second gas concentration detection sensor, wherein an upper limit value of the second concentration range is lower than an upper limit value of the first concentration range, and a lower limit value of the second concentration range is lower than a lower limit value of the first concentration range; outputting an indication value based on an output signal of the first gas concentration detection sensor when an output signal of the first gas concentration detection sensor indicates a gas concentration in the first concentration range and an output signal of the second gas concentration detection sensor indicates a gas concentration higher than the upper limit value of the second concentration range; outputting an indication value based on an output signal of the second gas concentration detection sensor when an output signal of the second gas concentration detection sensor indicates a gas concentration in the second concentration range and an output signal of the first gas concentration detection sensor indicates a gas concentration lower than the lower limit value of the first concentration range; outputting an indication value based on an output signal of either the first gas concentration detection sensor or the second gas concentration detection sensor when an output signal of the first gas concentration detection sensor indicates a gas concentration in the first concentration range and an output signal of the second gas concentration detection sensor indicates a gas concentration in the second concentration range; outputting either the lower limit value of the first concentration range or the upper limit value of the second concentration range as an indication value when an output signal of the first gas concentration detection sensor indicates a gas concentration lower than the lower limit value of the first concentration range and an output signal of the second gas concentration detection sensor indicates a gas concentration higher than the upper limit value of the second concentration range; and displaying the indication value output at an indication value display unit.

According to the present invention, there is provided a control method of an oxygen concentration meter for a lamination molding apparatus, comprising steps of: supplying an inert gas from an inert gas supply device into a chamber configured to cover a molding region where a desired three-dimensional molded object is formed; detecting at least an oxygen concentration in a first concentration range in the chamber with a first oxygen concentration detection sensor; detecting at least an oxygen concentration in a second concentration range in the chamber with a second oxygen concentration detection sensor, wherein an upper limit value of the second concentration range is lower than an upper limit value of the first concentration range, and a lower limit value of the second concentration range is lower than a lower limit value of the first concentration range; when the supply of the inert gas in the chamber is started by the inert gas supply device, outputting an indication value based on an output signal of the first oxygen concentration detection sensor when an output signal of the first oxygen concentration detection sensor indicates an oxygen concentration in the first concentration range, outputting an indication value based on an output signal of the second oxygen concentration detection sensor when an output signal of the first oxygen concentration detection sensor indicates an oxygen concentration lower than the lower limit value of the first concentration range and an output signal of the second oxygen concentration detection sensor indicates an oxygen concentration in the second concentration range, and outputting either the lower limit value of the first concentration range or the upper limit value of the second concentration range as an indication value for a predetermined time when an output signal of the first oxygen concentration detection sensor indicates an oxygen concentration lower than the lower limit value of the first concentration range and an output signal of the second oxygen concentration detection sensor indicates an oxygen concentration higher than the upper limit value of the second concentration range; and displaying the indication value on the indication value display unit.

According to the gas concentration meter, the control method of the gas concentration meter, the lamination molding apparatus and the control method of oxygen concentration meter for the lamination molding apparatus according to the present invention, even if a sensor for measuring a specific gas concentration, for instance, an oxygen concentration, has a detection error, it is capable of detecting a specific gas concentration without missing a detection range.

DETAILED DESCRIPTION

Embodiments will be described in detail with reference to drawings. The various features shown in the following embodiments can be combined with each other.

1. Configuration Example

FIG. 1is a diagram showing the configuration of a gas concentration meter1according to the present embodiment. As shown inFIG. 1, the gas concentration meter1includes a control unit11, an indication value display unit12, a first gas concentration detection sensor13-1, a second gas concentration detection sensor13-2, a first on-off valve14-1, a second on-off valve14-2, a gas supply port15, an ejector16, and a flowmeter17, and detects a gas concentration of a specific gas in the chamber2. The indication value display unit12, the first gas concentration detection sensor13-1, the second gas concentration detection sensor13-2, the first on-off valve14-1, the second on-off valve14-2, and the flowmeter17are connected to the control unit11. Further, the gas concentration meter1may include a regulator18. The regulator18may be connected to the control unit11.

Based on an output signal of the first gas concentration detection sensor13-1and an output signal of the second gas concentration detection sensor13-2, the control unit11determines and outputs an indication value of the concentration of a specific gas in the chamber2to be displayed on the indication value display unit12. The control unit11controls the first on-off valve14-1and the second on-off valve14-2. Furthermore, the control unit11may control the regulator18based on an output signal of the flowmeter17.

The indication value display unit12displays an indication value output from the control unit11.

The first gas concentration detection sensor13-1detects at least a gas concentration in the first concentration range. The first concentration range is not less than the lower limit value of the first concentration range and not more than the upper limit value of the first concentration range.

The second gas concentration detection sensor13-2detects at least a gas concentration in the second concentration range. The second concentration range is not less than the lower limit value of the second concentration range and not more than the upper limit value of the second concentration range. The upper limit value of the second concentration range is lower than the upper limit value of the first concentration range. The lower limit value of the second concentration range is lower than the lower limit value of the first concentration range.

The first on-off valve14-1is a valve for passing the gas sucked from the inside of the chamber2to the first gas concentration detection sensor13-1when opened, and is realized by, for instance, a two-way solenoid valve, and opens and closes the first flow path19-1through which the gas flows by a control signal from the control unit11.

The second on-off valve14-2is a valve for passing the gas sucked from the inside of the chamber2to the second gas concentration detection sensor13-2when opened, and is realized by, for instance, a two-way solenoid valve, and opens and closes the second flow path19-2through which the gas flows according by a control signal from the control unit11.

The gas supply port15is a supply port connected to a gas supply device (not shown) for supplying a predetermined gas into the chamber2through the ejector16. The predetermined gas supplied from the gas supply port15is a specific gas that can be detected by the first gas concentration detection sensor13-1and the second gas concentration detection sensor13-2, a gas other than a specific gas, or a mixed gas of both. The gas supplied from the gas supply port15may be a gas filled in the chamber2. Further, as long as the gas filled in the chamber2is supplied from another supply port (not shown), the gas supplied from the gas supply port15may be used only to detect the gas concentration in the chamber2.

The ejector16generates a suction force by means of which the driving fluid flows therein, and sucks the gas in the chamber2. The ejector16includes a gas inlet16a, a gas suction port16band a gas outlet16c, and generates a suction force at the gas suction port16bby means of which the driving fluid flows from the gas inlet16ato the gas outlet16c. The driving fluid at this time is a predetermined gas supplied from the gas supply device. The gas inlet16ais connected to the gas supply port15. The gas outlet16cis connected to the chamber2. The gas suction port16bis connected to the chamber2via a flow path19. The gas suction port16bsucks the gas in the chamber2by a suction force generated when the driving fluid flows. Specifically, the ejector16utilizes the gas supplied from the gas supply port15in the direction indicated by an arrow A as a driving fluid, sucks the gas from the chamber2in the direction indicated by an arrow B, and outflows the two toward the chamber2in the direction indicated by an arrow C.

The flow path19is divided into the first flow path19-1and the second flow path19-2on the way and then merges again. The first gas concentration detection sensor13-1and the first on-off valve14-1are provided in the first flow path19-1. The second gas concentration detection sensor13-2and the second on-off valve14-2are provided in the second flow path19-2. The first on-off valve14-1opens and closes the first flow path19-1. The second on-off valve14-2opens and closes the second flow path19-2. The first gas concentration detection sensor13-1detects a gas concentration of a specific gas in the gas in the chamber2sucked through the first flow path19-1. The second gas concentration detection sensor13-2detects a gas concentration of a specific gas in the gas in the chamber2sucked through the second flow path19-2.

The flowmeter17measures the flow rate of the gas sucked from the chamber2. Specifically, the flowmeter17measures the flow rate of the gas flowing through the flow path19. The flowmeter17may output a value indicating the flow rate to the control unit11as an output signal. The flow meter17may comprise a flow rate control valve (not shown) to have a function of adjusting the flow rate of the gas sucked from the chamber2to a predetermined flow rate on the basis of a control signal from the control unit11. The suction of the gas in the chamber2is stopped in a case where the gases in the chamber2are not sequentially supplied to the first gas concentration detection sensor13-1and the second gas concentration detection sensor13-2, the first gas concentration detection sensor13-1and the second gas concentration detection sensor13-2measure the gas concentration of the gas remaining in the flow path19after being sucked from the inside of the chamber2. When the flow rate measured by the flow meter17is lower than a predetermined flow rate, the control unit11may ignore the output signals of the first gas concentration detection sensor13-1and the second gas concentration detection sensor13-2to display a warning on the indication value display unit12.

The regulator18limits the pressure of the gas supplied from the gas supply port15to a predetermined pressure. The regulator18may limit the pressure of the gas supplied from the gas supply port15to a predetermined pressure based on a control signal from the control unit11. It should be noted that the flow rate of the gas sucked from the chamber2can also be adjusted by controlling the pressure or the flow rate of the gas serving as the driving fluid of the ejector16by the regulator18or a flow rate control valve (not shown) based on a control signal from the control unit11.

According to these configurations, for instance, when the first gas concentration detection sensor13-1detects the gas concentration, the control unit11opens the first on-off valve14-1and controls the second on-off valve14-2to close. At this time, the control unit11may control the flow rate control valve of the flowmeter17so that the measured value of the flowmeter17becomes a value suitable for the measurement environment of the first gas concentration detection sensor13-1. When the second gas concentration detection sensor13-2detects the gas concentration, the control unit11opens the second on-off valve14-2and controls the first on-off valve14-1to close. At this time, the control unit11may control the flow rate control valve of the flowmeter17so that the measured value of the flowmeter17becomes a value suitable for the measurement environment of the second gas concentration detection sensor13-2. That is, the control unit11opens the first on-off valve14-1when detecting the gas concentration in the first gas concentration detecting sensor13-1, and opens the second on-off valve14-2when the second gas concentration detecting sensor13-2detects the gas concentration, and controls the gas in the chamber2so as to supply the gas by switching either the first gas concentration detection sensor13-1or the second gas concentration detection sensor13-2. The first on-off valve14-1and the second on-off valve14-2may be replaced with, for example, one three-way solenoid valve. The first on-off valve14-1and the second on-off valve14-2may be replaced with a flow rate control valve (not shown). The flow rate control valves replaced from the first on-off valve14-1and the second on-off valve14-2are realized by, for example, an solenoid proportional valve, and can open and close the flow path19through which the gas flows, and adjust the flow rate of the gas suitable for the measurement environment of the first gas concentration detection sensor13-1and the second gas concentration detection sensor13-2.

The control unit11can simultaneously acquire both the output signal of the first gas concentration detection sensor13-1and the output signal of the second gas concentration detection sensor13-2. At this time, the first on-off valve14-1and the second on-off valve14-2are opened. Alternatively, the first on-off valve14-1and the second on-off valve14-2become unnecessary. The first on-off valve14-1and the second on-off valve14-2may be replaced by flow rate control valves, respectively. The control unit11opens each flow rate control valve replaced with the first on-off valve14-1and the second on-off valve14-2according to the ratio between the flow rate of the gas suitable for the first gas concentration detection sensor13-1and the flow rate of the gas suitable for the second gas concentration detection sensor13-2, the flow rate control valve of the flowmeter17is controlled so that the measured value of the flowmeter17is the sum of the flow rate of the gas suitable for the measurement environment of the first gas concentration detection sensor13-1and the flow rate of the gas suitable for the measurement environment of the second gas concentration detection sensor13-2, both the output signal of the first gas concentration detection sensor13-1and the output signal of the second gas concentration detection sensor13-2can be simultaneously acquired.

2. Selection of Indication Values

Next, the indication value output by the control unit11will be described with reference toFIGS. 2 to 4.

FIG. 2is a diagram showing a concentration range in a case where a part of the first concentration range in which the first gas concentration detection sensor13-1detects a gas concentration and the second concentration range in which the second gas concentration detection sensor13-2detects a gas concentration overlap each other.

In the example shown inFIG. 2, the first gas concentration detection sensor13-1detects a gas concentration in a range from a to b, and the second gas concentration detection sensor13-2detects a gas concentration in a range from z to c.

FIG. 3is a diagram showing a concentration range in a case where the upper limit value of the first concentration range in which the first gas concentration detection sensor13-1detects the gas concentration and the upper limit value of the second concentration range in which the second gas concentration detection sensor13-2detects the gas concentration are the same.

In the example shown inFIG. 3, the first gas concentration detection sensor13-1detects a gas concentration in a range from d to e, and the second gas concentration detection sensor13-2detects a gas concentration in a range from z to d.

FIG. 4is a diagram showing a concentration range in a case where the first concentration range in which the first gas concentration detection sensor13-1detects the gas concentration and the second concentration range in which the second gas concentration detection sensor13-2detects the gas concentration are separated from each other.

In the example shown inFIG. 4, the first gas concentration detection sensor13-1detects a gas concentration in a range from f to g, and the second gas concentration detection sensor13-2detects a gas concentration in a range from z to h.

When the output signal of the first gas concentration detection sensor13-1indicates a gas concentration in the first concentration range and the output signal of the second gas concentration detection sensor13-2indicates a gas concentration higher than the upper limit value of the second concentration range, the control unit11outputs an indication value based on the output signal of the first gas concentration detection sensor13-1.

Specifically, when the first concentration range and the second concentration range are as shown inFIG. 2, the output signal of the first gas concentration detection sensor13-1is not less than a and not more than b, and when the output signal of the second gas concentration detection sensor13-2is higher than c, the control unit11outputs an indication value based on the output signal of the first gas concentration detection sensor13-1.

When the first concentration range and the second concentration range are as shown inFIG. 3, the output signal of the first gas concentration detection sensor13-1is not less than d and not more than e, and when the output signal of the second gas concentration detection sensor13-2is higher than d, the control unit11outputs an indication value based on the output signal of the first gas concentration detection sensor13-1.

When the first concentration range and the second concentration range are as shown inFIG. 4, the output signal of the first gas concentration detection sensor13-1is not less than f and not more than g, and when the output signal of the second gas concentration detection sensor13-2is higher than h, the control unit11outputs an indication value based on the output signal of the first gas concentration detection sensor13-1.

When the output signal of the second gas concentration detection sensor13-2indicates the gas concentration in the second concentration range and the output signal of the first gas concentration detection sensor13-1indicates a gas concentration lower than the lower limit value of the first concentration range, the control unit11outputs an indication value based on the output signal of the second gas concentration detection sensor13-2.

Specifically, when the first concentration range and the second concentration range are as shown inFIG. 2, the output signal of the second gas concentration detection sensor13-2is not less than z and not more than c, and when the output signal of the first gas concentration detection sensor13-1is lower than a, the control unit11outputs an indication value based on the output signal of the second gas concentration detection sensor13-2.

When the first concentration range and the second concentration range are as shown inFIG. 3, the output signal of the second gas concentration detection sensor13-2is not less than z and not more than d, and when the output signal of the first gas concentration detection sensor13-1is lower than d, the control unit11outputs an indication value based on the output signal of the second gas concentration detection sensor13-2.

When the first concentration range and the second concentration range are as shown inFIG. 4, the output signal of the second gas concentration detection sensor13-2is not less than z and not more than h, and when the output signal of the first gas concentration detection sensor13-1is lower than f, the control unit11outputs an indication value based on the output signal of the second gas concentration detection sensor13-2.

Furthermore, when the control unit11indicates the gas concentration in the first concentration range of the output signal of the first gas concentration detection sensor13-1and the output signal of the second gas concentration detection sensor13-2indicates the gas concentration in the second concentration range, an indication value is output based on the output signal from either the first gas concentration detection sensor13-1or the second gas concentration detection sensor13-2.

Whether the control unit11outputs an indication value based on the output signal from either the first gas concentration detection sensor13-1or the second gas concentration detection sensor13-2can be determined in advance. When it is determined that an indication value based on the output signal of the first gas concentration detection sensor13-1is to be output, the control unit11outputs an indication value based on the output signal of the first gas concentration detection sensor13-1regardless of the output signal of the second gas concentration detection sensor13-2when the output signal of the first gas concentration detection sensor13-1indicates a gas concentration in the first concentration range.

When it is determined that an indication value based on the output signal of the second gas concentration detection sensor13-2is to be output, the control unit11outputs an indication value based on the output signal of the second gas concentration detection sensor13-2regardless of the output signal of the first gas concentration detection sensor13-1when the output signal of the second gas concentration detection sensor13-2indicates a gas concentration in the second concentration range.

Specifically, when the first concentration range and the second concentration range are as shown inFIG. 2, an output signal of the first gas concentration detection sensor13-1is not less than a and not more than b, and when the output signal of the second gas concentration detection sensor13-2is not less than z and not more than c, the control unit11outputs an indication value based on an output signal of one of the first gas concentration detection sensor13-1and the second gas concentration detection sensor13-2.

In addition, when the first concentration range and the second concentration range are as shown inFIG. 3, the output signal of the first gas concentration detection sensor13-1is not less than d and not more than e, and when the output signal of the second gas concentration detection sensor13-2is not less than z and not more than d, the control unit11outputs an indication value based on an output signal of either the first gas concentration detection sensor13-1or the second gas concentration detection sensor13-2.

Further, when the first concentration range and the second concentration range are as shown inFIG. 4, the output signal of the first gas concentration detection sensor13-1is not less than f and not more than g, and when the output signal of the second gas concentration detection sensor13-2is not less than z and not more than h, the control unit11outputs an indication value based on an output signal of either the first gas concentration detection sensor13-1or the second gas concentration detection sensor13-2.

Furthermore, when the control unit11indicates a gas concentration lower than the lower limit value of the first concentration range by the output signal of the first gas concentration detection sensor13-1, and the output signal of the second gas concentration detection sensor13-2indicates a gas concentration higher than the upper limit value of the second concentration range, either the lower limit value of the first concentration range or the upper limit value of the second concentration range is output as an indication value. At this time, the control unit11may preferably outputs an indication value for a predetermined time, and thereafter, newly outputs an indication value based on an output signal of the first gas concentration detection sensor13-1and the second gas concentration detection sensor13-2.

In addition, when the control unit11indicates a gas concentration lower than the lower limit value of the first concentration range by the output signal of the first gas concentration detection sensor13-1, and when the output signal of the second gas concentration detection sensor13-2indicates a gas concentration higher than the upper limit value of the second concentration range, the lower limit value of the first concentration range may be output as an indication value if the immediately preceding indication value is a value based on the output signal of the first gas concentration detection sensor13-1or the lower limit value of the first concentration range, and the upper limit value of the second concentration range may be output as an indication value if the immediately preceding indication value is a value based on the output signal of the second gas concentration detection sensor13-2or the upper limit value of the second concentration range. At this time, the control unit11may preferably output the indication value for a predetermined time.

Further, when the control unit11indicates a gas concentration lower than the lower limit value of the first concentration range by an output signal of the first gas concentration detection sensor13-1, and when the output signal of the second gas concentration detection sensor13-2indicates a gas concentration higher than the upper limit of the second concentration range, whichever one of the lower limit value of the first concentration range and the upper limit value of the second concentration range is higher than the upper limit value may be output as the indication value. At this time, the control unit11may preferably output the indication value for a predetermined time.

Furthermore, when the control unit11indicates a gas concentration lower than the lower limit value of the first concentration range by the output signal of the first gas concentration detection sensor13-1, and when the output signal of the second gas concentration detection sensor13-2indicates a gas concentration higher than the upper limit value of the second concentration range, if the unit of the first concentration range and the unit of the second concentration range are different even when the lower limit value of the first concentration range is the same as the upper limit value of the second concentration range, either the lower limit value of the first concentration range or the upper limit value of the second concentration range may be output as an indication value. At this time, the control unit11may preferably output the indication value for a predetermined time.

Specifically, when the first concentration range and the second concentration range are as shown inFIG. 2, if the output signal of the first gas concentration detection sensor13-1is lower than a and the output signal of the second gas concentration detection sensor13-2is higher than c, then the control unit11outputs either a or c as an indication value. At this time, the control unit11may preferably output either a or c as an indication value for a predetermined time.

In addition, when the first concentration range and the second concentration range are as shown inFIG. 2, if the output signal of the first gas concentration detection sensor13-1is lower than a and the output signal of the second gas concentration detection sensor13-2is higher than c, the control unit11may output a as an indication value if the immediately preceding indication value is the output signal of the first gas concentration detection sensor13-1or a, and may output c as an indication value if the immediately preceding indication value is the output signal of the second gas concentration detection sensor13-2or c. At this time, the control unit11may preferably output the indication value for a predetermined time.

Further, when the first concentration range and the second concentration range are as shown inFIG. 2, if the output signal of the first gas concentration detection sensor13-1is lower than a and the output signal of the second gas concentration detection sensor13-2is higher than c, then the control unit11may output c as an indication value which is higher than a. At this time, the control unit11may preferably output c which is higher than a as an indication value for a predetermined time.

Furthermore, when the first concentration range and the second concentration range are as shown inFIG. 3, if the output signal of the first gas concentration detection sensor13-1is lower than d and the output signal of the second gas concentration detection sensor13-2is higher than d, then the control unit11outputs d as an indication value. At this time, the control unit11may preferably output d as an indication value for a predetermined time.

Moreover, when the first concentration range and the second concentration range are as shown inFIG. 3, if the output signal of the first gas concentration detection sensor13-1is lower than d and the output signal of the second gas concentration detection sensor13-2is higher than d, then the control unit11may output either the lower limit value of the first concentration range or the upper limit value of the second concentration range as an indication value if the unit of the first concentration range and the second concentration range are different. At this time, the control unit11may preferably output the indication value for a predetermined time.

Further, when the first concentration range and the second concentration range are as shown inFIG. 4, if the output signal of the first gas concentration detection sensor13-1is lower than f and the output signal of the second gas concentration detection sensor13-2is higher than h, then the control unit11outputs either for h as an indication value. At this time, the control unit11may preferably output either f or h as an indication value for a predetermined time.

In addition, when the first concentration range and the second concentration range are as shown inFIG. 4, if the output signal of the first gas concentration detection sensor13-1is lower than f and the output signal of the second gas concentration detection sensor13-2is higher than h, the control unit11may output f as an indication value if the immediately preceding indication value is the output signal of the first gas concentration detection sensor13-1or f, and may output h as an indication value if the immediately preceding indication value is the output signal of the second gas concentration detection sensor13-2or h. At this time, the control unit11may preferably output the indication value for a predetermined time.

Moreover, when the first concentration range and the second concentration range are as shown inFIG. 4, if the output signal of the first gas concentration detection sensor13-1is lower than f and the output signal of the second gas concentration detection sensor13-2is higher than h, then the control unit11may output f which has a higher value than h as an indication value. At this time, the control unit11may preferably output f which is higher than h as an indication value for a predetermined time.

3. Output Signal Error

Incidentally, when the indication value based on the output signal of the first gas concentration detection sensor13-1and the indication value based on the output signal of the second gas concentration detection sensor13-2are different, although the control unit11selects one of these, the reason why the indication value based on the output signal of the first gas concentration detection sensor13-1and the indication value based on the output signal of the second gas concentration detection sensor13-2are different, and the reason why it is permissible to select one of them will be described.

The reason why the indication value based on the output signal of the first gas concentration detection sensor13-1and the output signal of the second gas concentration detection sensor13-2are different is due to the detection error of the first gas concentration detection sensor13-1and the detection error of the second gas concentration detection sensor13-2.

Hereinafter, the detection error will be described.FIG. 5is a diagram illustrating an error in the concentration range shown inFIG. 2. Moreover,FIG. 6is a diagram illustrating an error in the concentration range shown inFIG. 3.

It is assumed that the detection error of the first gas concentration detection sensor13-1is 1% with respect to the full scale (FS), and the detection error of the second gas concentration detection sensor13-2is 5% with respect to the full scale. In this case, in the example of the concentration range shown inFIG. 2, even if the indication value based on the output signal of the first gas concentration detection sensor13-1is a, the actual gas concentration value may be in the range of a−b/100 or more and a+b/100 or less. On the other hand, even if the indication value based on the output signal of the second gas concentration detection sensor13-2is c, the actual gas concentration value may be in the range of c−c/20 or more and c+c/20 or less.

Similarly, in the example of the concentration range shown inFIG. 3, even if the indication value based on the output signal of the first gas concentration detection sensor13-1is d, the actual gas concentration value may be in a range of d−e/100 or more and d+e/100 or less. On the other hand, even if the indication value based on the output signal of the second gas concentration detection sensor13-2is d, the actual gas concentration value may be in a range of d−d/20 or more and d+d/20 or less.

As described above, in the vicinity of the boundary between the first concentration range and the second concentration range, there are cases where the indication value based on the output signal of the first gas concentration detection sensor13-1and the indication value based on the output signal of the second gas concentration detection sensor13-2are different, or both may indicate values deviated from the concentration range.

However, even if the indication value based on the output signal of the first gas concentration detection sensor13-1and the indication value based on the output signal of the second gas concentration detection sensor13-2are different, any value is in the allowable range since each value is within the range of the detection error.

In the case of the concentration range shown inFIG. 4, since the first concentration range and the second concentration range are separated from each other, and it is clear that the value in the vicinity of the boundary between the first concentration range and the second concentration range is not required at the design stage, there is no problem that the indication value based on the output signal of the first gas concentration detection sensor13-1is different from the indication value based on the output signal of the second gas concentration detection sensor13-2.

4. Operation of Control Unit11

Next, an operation flow of the control unit11will be described.FIG. 7is an activity diagram showing a flow of an operation of the control unit11when the detection of the gas concentration is started from the detection of the gas concentration by the first gas concentration detection sensor. Moreover,FIG. 8is an activity diagram showing a flow of an operation of the control unit11when the detection of the gas concentration is started from the detection of the gas concentration by the second gas concentration detection sensor.

When the detection of the gas concentration is started from the detection of the gas concentration by the first gas concentration detection sensor13-1, the control unit11first acquires an output signal of the first gas concentration detection sensor13-1(A101). As a result, if the indication value based on the output signal is in the first concentration range, the indication value is displayed on the indication value display unit12(A102), and the output signal of the first gas concentration detection sensor13-1is acquired again.

On the other hand, if the indication value based on the output signal is lower than the lower limit value of the first concentration range, the control unit11acquires the output signal of the second gas concentration detection sensor13-2(A103). As a result, if the indication value based on the output signal is higher than the upper limit value of the second concentration range, the control unit11displays the lower limit value of the first concentration range on the indication value display unit12(A104), waits for a predetermined time (A105), and acquires the output signal of the first gas concentration detection sensor13-1again.

If the indication value based on the output signal of the second gas concentration detection sensor13-2is in the second concentration range, the control unit11displays the indication value on the indication value display unit12(A106).

Thereafter, the control unit11operates in the same manner as in the case where the detection of the gas concentration is started from the detection of the gas concentration by the second gas concentration detection sensor13-2.

When the detection of the gas concentration is started from the detection of the gas concentration by the second gas concentration detection sensor13-2, the control unit11first acquires an output signal of the second gas concentration detection sensor13-2(A201). As a result, if the indication value based on the output signal is in the second concentration range, the indication value is displayed on the indication value display unit12(A202), and the output signal of the second gas concentration detection sensor13-2is acquired again.

On the other hand, if the indication value based on the output signal is higher than the upper limit value of the second concentration range, the control unit11acquires the output signal of the first gas concentration detection sensor13-1(A203). If the indication value based on the output signal is lower than the lower limit value of the first concentration range, the control unit11displays the upper limit of the second concentration range on the indication value display unit12(A204), waits for a predetermined time (A205), and acquires the output signal of the second gas concentration detection sensor13-2again.

Further, when the indication value based on the output signal of the first gas concentration detection sensor13-1is in the first concentration range, the control unit11displays the indication value on the indication value display unit12(A206).

Thereafter, the control unit11operates in the same manner as in the case where the detection of the gas concentration is started from the detection of the gas concentration by the first gas concentration detection sensor13-1.

FIG. 9is a diagram showing the configuration of a lamination molding apparatus5according to the present embodiment. As shown inFIG. 9, the lamination molding apparatus5includes at least a chamber6, an inert gas supply device7, and an oxygen concentration meter8. It should be noted that the description of the general configuration of the lamination molding apparatus5is omitted.

The chamber6is configured to cover a molding region in which a desired three-dimensional molded object is formed. In the chamber6, a table having a molding region where a desired three-dimensional molded object is formed, a powder layer forming unit for forming a powder layer of a metal material powder in the molding region, and the like are arranged.

The inert gas supply device7fills the chamber with an inert gas.

The oxygen concentration meter8includes a control unit81, an indication value display unit82, a first oxygen concentration detection sensor83-1, a second oxygen concentration detection sensor83-2, a first on-off valve84-1, a second on-off valve84-2, a gas supply port85, an ejector86, and a flowmeter87, and detects the oxygen concentration in the chamber6. The indication value display unit82, the first oxygen concentration detection sensor83-1, the second oxygen concentration detection sensor83-2, the first on-off valve84-1, the second on-off valve84-2, and the flowmeter87are connected to the control unit81. The oxygen concentration meter8may include a regulator88. The regulator88may be connected to the control unit81.

Based on the output signal of the first oxygen concentration detection sensor83-1and the output signal of the second oxygen concentration detection sensor83-2, the control unit81determines and outputs an indication value of the oxygen concentration in the chamber6to be displayed on the indication value display unit82. The control unit81controls the first on-off valve84-1and the second on-off valve84-2. Moreover, the control unit81may control the regulator88based on the output signal of the flowmeter87.

The indication value display unit82displays an indication value output from the control unit81.

The first oxygen concentration detection sensor83-1detects at least an oxygen concentration in the first concentration range.

The second oxygen concentration detection sensor83-2detects at least an oxygen concentration in a range including the second concentration range. The upper limit value of the second concentration range is lower than the upper limit value of the first concentration range, and the lower limit value of the second concentration range is lower than the lower limit value of the first concentration range.

The first on-off valve84-1is a valve for passing the gas sucked from the inside of the chamber6when opened to the first oxygen concentration detection sensor83-1and is realized by, for example, a two-way solenoid valve, and opens and closes the first flow path89-1through which the gas flows according to a control signal from the control unit81.

The second on-off valve84-2is a valve for passing the gas sucked from the inside of the chamber6when opened to the second oxygen concentration detection sensor83-2and is realized by, for example, a two-way solenoid valve, and opens and closes the first flow path89-1through which the gas flows according to a control signal from the control unit81.

The gas supply port85is a supply port for supplying an inert gas into the chamber6through the ejector86. The gas supply port85is connected to the inert gas supply device7. The inert gas supplied from the gas supply port85is filled in the chamber6. Moreover, if the inert gas filled in the chamber6is supplied from another supply port (not shown), the inert gas supplied from the gas supply port85may be used only to detect the oxygen concentration in the chamber6.

The ejector86generates a suction force by means of which the driving fluid flows therein, and sucks the gas in the chamber6. The ejector86includes a gas inlet86e, a gas suction port86f, and a gas outlet86g, and generates a suction force at the gas suction port86fby means of which the driving fluid flows from the gas inlet86eto the gas outlet86g. The driving fluid at this time is an inert gas supplied from the inert gas supply device7. The gas inlet86eis connected to the gas supply port85. The gas outlet86gis connected to the chamber6. The gas suction port86fis connected to the chamber6via a flow path89. The gas suction port86fsucks the gas in the chamber6by a suction force generated when the driving fluid flows. Specifically, the ejector86utilizes the inert gas supplied from the gas supply port85in a direction indicated by an arrow E as a driving fluid, sucks the gas from the chamber6in a direction indicated by an arrow F, and outflows the two toward the chamber6in the direction indicated by an arrow G.

The flow path89is divided into the first flow path89-1and the second flow path89-2on the way and then merges again. The first oxygen concentration detection sensor83-1and the first on-off valve84-1are provided in the first flow path89-1. The second oxygen concentration detection sensor83-2and the second on-off valve84-2are provided in the second flow path89-2. The first on-off valve84-1opens and closes the first flow path89-1. The second on-off valve84-2opens and closes the second flow path89-2. The first oxygen concentration detection sensor83-1detects the oxygen concentration in the gas in the chamber6sucked through the first flow path89-1. The second oxygen concentration detection sensor83-2detects the oxygen concentration in the gas in the chamber6sucked through the second flow path89-2.

The flowmeter87measures the flow rate of the gas sucked from the chamber6. Specifically, the flowmeter87measures the flow rate of the gas flowing through the flow path89. The flowmeter87may output a value indicating the flow rate to the control unit81as an output signal. The flow meter87may have a flow rate control valve (not shown) to have a function of adjusting the flow rate of the gas sucked from the chamber6to a predetermined flow rate on the basis of a control signal from the control unit81. Note that when the suction of the gas in the chamber6is stopped and the gas in the chamber6is not sequentially supplied to the first oxygen concentration detection sensor83-1and the second oxygen concentration detection sensor83-2, the first oxygen concentration detection sensor83-1and the second oxygen concentration detection sensor83-2measure the oxygen concentration of the gas remaining in the flow path89after being sucked from the inside of the chamber6. When the flow rate measured by the flowmeter87is lower than the predetermined flow rate, the control unit81may ignore the output signals of the first oxygen concentration detection sensor83-1and the second oxygen concentration detection sensor83-2and display a warning on the indication value display unit82.

The regulator88limits the pressure of the inert gas supplied from the gas supply port85to a predetermined pressure. The regulator88may limit the pressure of the inert gas supplied from the gas supply port85to a predetermined pressure based on a control signal from the control unit81. The flow rate of the gas sucked from the chamber6can also be adjusted by controlling the pressure or the flow rate of the gas to be the driving fluid of the ejector86by the regulator88or a flow rate control valve (not shown) based on a control signal from the control unit81.

According to these configurations, for example, when the oxygen concentration is detected by the first oxygen concentration detection sensor83-1, the control unit81opens the first on-off valve84-1and controls the second on-off valve84-2to close. At this time, the control unit81may control the flow rate control valve of the flowmeter87so that the measured value of the flowmeter87becomes a value suitable for the measurement environment of the first oxygen concentration detection sensor83-1. When the second oxygen concentration detection sensor83-2detects the oxygen concentration, the control unit81opens the second on-off valve84-2and controls the first on-off valve84-1to close. At this time, the control unit81may control the flow rate control valve of the flowmeter87so that the measured value of the flowmeter87becomes a value suitable for the measurement environment of the second oxygen concentration detection sensor83-2. That is, the control unit81opens the first on-off valve84-1when the oxygen concentration is detected by the first oxygen concentration detecting sensor83-1, opens the second on-off valve84-2when the oxygen concentration is detected by the second oxygen concentration detecting sensor83-2, and controls the gas in the chamber6so as to supply the gas by switching either the first oxygen concentration detection sensor83-1or the second oxygen concentration detection sensor83-2. The first on-off valve84-1and the second on-off valve84-2may be replaced with, for example, one three-way solenoid valve. Further, the first on-off valve84-1and the second on-off valve84-2may be replaced with flow rate control valves (not shown), respectively. Each flow rate control valve replaced from the first on-off valve84-1and the second on-off valve84-2is realized by, for example, an solenoid proportional valve, and can open and close the flow path89through which the gas flows based on the control signal from the control unit11and adjust the flow rate of the gas suitable for the measurement environment of the first oxygen concentration detection sensor83-1and the second oxygen concentration detection sensor83-2.

It should be noted that the control unit81can simultaneously acquire both the output signal of the first oxygen concentration detection sensor83-1and the output signal of the second oxygen concentration detection sensor83-2. At this time, the first on-off valve84-1and the second on-off valve84-2are opened respectively. Alternatively, the first on-off valve84-1and the second on-off valve84-2become unnecessary. The first on-off valve84-1and the second on-off valve84-2may be replaced with the flow rate control valves, respectively. The control unit81opens each flow rate control valve replaced from the first on-off valve84-1and the second on-off valve84-2according to the ratio between the flow rate of the gas suitable for the first oxygen concentration detection sensor83-1and the flow rate of the gas suitable for the second oxygen concentration detection sensor83-2, the flow rate control valve of the flowmeter87is controlled so that the measured value of the flowmeter87is the sum of the flow rate of the gas suitable for the measurement environment of the first oxygen concentration detection sensor83-1and the flow rate of the gas suitable for the measurement environment of the second oxygen concentration detection sensor83-2, both the output signal of the first oxygen concentration detection sensor83-1and the output signal of the second oxygen concentration detection sensor83-2can be simultaneously acquired.

6. Selection of Indication Values

Since the method of selecting the indication value by the control unit81is the same as replacing the “gas concentration” with “oxygen concentration” in the above description of the selection of the indication value by the control unit11, the description thereof will be omitted.

7. Operation of Control Unit81

Next, an operation flow of the control unit81will be described.FIG. 10is an activity diagram showing a flow of an operation of a control unit81when the detection of the oxygen concentration is started by the first oxygen concentration detection sensor. Further,FIG. 11is an activity diagram showing a flow of an operation of the control unit81when the detection of the oxygen concentration is started by the second oxygen concentration detection sensor.

First, the control unit81acquires an output signal of the first oxygen concentration detection sensor83-1(A301). As a result, if the indication value based on the output signal is in the first concentration range, the indication value is displayed on the indication value display unit82(A302), and the output signal of the first oxygen concentration detection sensor83-1is acquired again.

On the other hand, if the indication value based on the output signal is lower than the lower limit value of the first concentration range, the control unit81acquires the output signal of the second oxygen concentration detection sensor83-2(A303). As a result, if the indication value based on the output signal is higher than the upper limit value of the second concentration range, the control unit81displays the lower limit value of the first concentration range on the indication value display unit82(A304), waits for a predetermined time (A305), and acquires the output signal of the first oxygen concentration detection sensor83-1again.

If the indication value based on the output signal of the second oxygen concentration detection sensor83-2is in the second concentration range, the control unit81displays the indication value on the indication value display unit82(A306), and then starts the detection of the oxygen concentration by the second oxygen concentration detection sensor83-2.

The control unit81first acquires an output signal of the second oxygen concentration detection sensor83-2(A401). As a result, if the indication value based on the output signal is in the second concentration range, the indication value is displayed on the indication value display unit82(A402), and the output signal of the second oxygen concentration detection sensor83-2is acquired again.

On the other hand, if the indication value based on the output signal is higher than the upper limit value of the second concentration range, the control unit81acquires the output signal of the first oxygen concentration detection sensor83-1(A403). Therefore, if the indication value based on the output signal is lower than the lower limit value of the first concentration range, the control unit11displays the upper limit value of the second concentration range on the indication value display unit12(A404), waits for a predetermined time (A405), and acquires the output signal of the second oxygen concentration detection sensor83-2again.

Moreover, if the indication value based on the output signal of the first oxygen concentration detection sensor83-1is in the first concentration range, the control unit81displays the indication value on the indication value display unit12(A406), and then starts to detect the oxygen concentration by the first oxygen concentration detection sensor83-1.

It should be noted that when filling the chamber6with the inert gas, it is necessary for the lamination molding apparatus5to confirm whether the degree of filling is sufficient or not. However, it is unnecessary to detect the oxygen concentration when exhausting the inert gas from the chamber6, thus the control unit81operates differently from the control unit11described above.