Patent Description:
Conventionally, a balance using a windshield for which an opening and closing door to be automatically opened and closed by a driving means is suspended at an upper end portion is known, and a lower end portion as a free end of the opening and closing door is generally guided by a groove provided in a guide rail. However, while a specimen is placed on a weighing pan inside a weighing chamber surrounded by the windshield, the specimen is sometimes spilled on the inside of the weighing chamber or the guide rail, and when cleaning this, it is difficult to completely clean out the specimen that has fallen into the groove of the guide rail. Further, in the groove, dust is also likely to accumulate naturally, and it is also difficult to completely clean out such dust. Such a specimen or dust remaining in the groove poses a problem in which it will obstruct smooth opening and closing operations of the opening and closing door.

To eliminate this problem, conventionally, a configuration is provided such that, without providing the guide rail, a floor portion of the weighing chamber is formed into a truncated pyramid shape and inclined so as to become lower toward a peripheral edge, and the peripheral edge is brought into contact with a lower inner side surface of the opening and closing door to guide movements of the opening and closing door (Patent Literature <NUM>), and a configuration is proposed in which movements of the opening and closing door are guided by a guide rail formed of a stepped portion having an L-shaped cross-section without a groove portion (Patent Literature <NUM>). Further background art for the present invention is described in Patent Literature <NUM>-<NUM>.

In Patent Literature <NUM>, a pair of horizontally slidable side wall portions (opening and closing doors) are held at vertical positions, and are pushed by a biasing torque, lower inner side surfaces of the side wall portions facing boundary end portions as peripheral edges of the floor surface always face and are in contact with the boundary end portions, and define a weighing chamber as a closed space. In this way, the side wall portions need to be always in close contact with the boundary end portions by a biasing torque in order to define the closed space, which poses a problem in which friction is great to make smooth sliding of the pair of side wall portions (opening and closing doors) difficult, and for sliding the side wall portions, a great driving force is needed.

On the other hand, in Patent Literature <NUM>, in a case of opening or closing the pair of sliding windows (opening and closing doors) together, locks of grips at lower sides, respectively fixed to both sides of a plate provided movably on a bottom portion of the weighing chamber, are inserted into and integrated with lower ends of bars respectively fixed to the sliding windows, so that lower portions of the respective sliding windows do not wobble. However, when it is desired to move the respective sliding windows separately, the locks of the lower-side grips inserted into the lower ends of the bars are detached and released from being integrated with each other, so that there is a problem that lower ends of the respective sliding windows are guided in contact with bottom surface portions of the guide rails, but they become free in thickness directions of the lower ends, so that during movement, the lower portions of the respective sliding windows wobble in the thickness directions to impair sealability of the weighing chamber. To prevent this wobbling, when the bottom surface portions and the lower ends of the sliding windows are brought into firm contact with each other, a problem occurs in that friction becomes greater to make a smooth movement of the respective sliding windows difficult.

An object of the present invention is to provide a windshield for a balance, including opening and closing doors from which the problems described above have been eliminated.

In order to solve the problems described above, a windshield for a balance according to the present invention is a windshield covering a weighing pan to define a weighing chamber, and the windshield has a front surface portion, a pair of side surface portions, a back surface portion, and an upper surface portion, the pair of side surface portions are respectively opening and closing doors for opening and closing side surfaces of the weighing chamber, upper portions of said opening and closing doors being supported movably by holding portions provided along respective side portions of the upper surface portion, and lower portions being guided by guide rails each formed of a horizontal portion and a vertical portion, configured to be reciprocated by a driving means, and on the horizontal portions of the respective guide rails, restricting members configured to restrict lower ends of the respective opening and closing doors from being displaced in separating directions from the vertical portions of the respective guide rails are provided along movement paths of the respective opening and closing doors.

As described above, each guide rail is formed of a horizontal portion and a vertical portion, and has no groove, so that dust does not accumulate in the guide rail, and even if dust or a specimen adheres to the guide rail, it can be easily cleaned out and thus be easily cleaned, so that smooth movements of the respective opening and closing doors are not obstructed by dust and a specimen. In addition, the restricting members configured to restrict the lower ends of the respective opening and closing doors from being displaced in separating directions from the vertical portions of the respective guide rails are provided, so that lower portions of the respective opening and closing doors do not wobble.

Moreover, by a configuration in which lower ends of the respective opening and closing doors are positioned at distances from the horizontal portions of the guide rails and positioned at a height not higher than upper ends of the vertical portions, while outside air is reliably prevented from flowing into the weighing chamber, and even if a specimen or dust remains on the horizontal portions, it does not obstruct reciprocating motions of the opening and closing doors, and the respective opening and closing doors are smoothly reciprocated.

Further, the driving means is configured by air cylinders provided outside the weighing chamber for each of the respective opening and closing doors, each of the air cylinders is joined, at a tip end of a piston rod capable of projecting out and retreating, to an end portion at the front surface portion sides of the opening and closing door, and the restricting member is provided so as to be positioned closer to the back surface portion than the portion joined to the opening and closing door, that is, positioned at the opposite side to the front surface portion, in a state where the piston rod of the air cylinder is retreating most, and accordingly, smooth movements of the opening and closing door by the driving means and restriction by the restricting member in the entire range of the movements are reliably secured. Moreover, because lower portions of the opening and closing doors do not wobble, excessive loads are also not applied when the driving means operates.

Furthermore, by configuring the restricting member by one projection, friction between the projection serving as the restricting member and the opening and closing door becomes smaller, and the movements of the opening and closing door become smoother.

According to the present invention, in a windshield defining a weighing chamber, opening and closing doors that open and close side surfaces of the weighing chamber are guided by guide rails without grooves, and lower portions of the opening and closing doors are prevented from wobbling, so that not only does cleaning become easy, but the inside of the weighing chamber can be reliably shut off from the outside, and excessive unnecessary loads are not applied to the driving means, and the opening and closing doors can be smoothly reciprocated.

Hereinafter, a preferred embodiment of the present invention will be described based on the attached drawings.

As illustrated in <FIG>, a balance <NUM> includes an electronic balance <NUM> and a windshield <NUM>. The electronic balance <NUM> includes a weighing pan <NUM> for placing a specimen on its upper surface. The windshield <NUM> may be detachably attached to the electronic balance <NUM> by a publicly known attaching and detaching mechanism, or may be integrated with the electronic balance <NUM> in a non-separable manner. The windshield <NUM> is installed on an upper surface of the electronic balance <NUM> so as to surround a periphery of the weighing pan <NUM>, and prevents air flows around the weighing pan <NUM>, for example, wind from an air conditioner, breath of a person at the time of weighing, air flow generated when a person walks, etc., from acting as a wind pressure on a load-applied portion centered on the weighing pan <NUM> and influencing weighing.

The windshield <NUM> has a bottomless box shape, and has a front glass <NUM> as a front surface portion, opening and closing doors <NUM> and <NUM> as a pair of side surface portions, a box-shaped case <NUM> as a back surface portion, and an upper surface door <NUM> as an upper surface portion, and covers the weighing pan <NUM> by the front glass <NUM>, the pair of opening and closing doors <NUM> and <NUM>, a front surface wall 14b of the case <NUM>, and the upper surface door <NUM> to define a weighing chamber S having a substantially rectangular parallelepiped shape. The front glass <NUM>, the pair of opening and closing doors <NUM> and <NUM>, and the upper surface door <NUM> are made of a transparent glass or resin material so that an internal state can be observed. However, the windshield <NUM> may be configured to have a shape other than a bottomless box shape.

The opening and closing doors <NUM> and <NUM> are suspended by being supported at their upper portions slidably by upper frames <NUM> and <NUM> as holding portions provided along respective side portions of the upper surface door <NUM> and cylinder boxes <NUM> and <NUM>. The opening and closing doors <NUM> and <NUM> are reciprocated, with their lower portions moving along guide rails <NUM> and <NUM> each formed of a horizontal portion 18a and a vertical portion 18b provided in a lower frame <NUM> serving as a frame member of a lower portion of the windshield <NUM>, by air cylinders <NUM> (only one air cylinder is illustrated) disposed inside the cylinder boxes <NUM> and <NUM>.

Further, the upper surface door <NUM> is movable forward and rearward along guide grooves 30a (refer to <FIG>) provided in the cylinder boxes <NUM> and <NUM> located at left and right sides of an upper portion of the windshield <NUM>.

To the opening and closing doors <NUM> and <NUM> and the upper surface door <NUM>, handles 11a, 11a, and 13a are respectively attached so that the doors are manually moved. The opening and closing doors <NUM> and <NUM> can be driven not only manually but also automatically by the air cylinders <NUM>.

Moreover, a control panel <NUM> is for operating the balance <NUM> and the opening and closing doors <NUM> and <NUM> of the windshield <NUM>, and provided separately from the balance <NUM> and the windshield <NUM>. The separate provision is for preventing vibrations by operations such as pushing a switch from influencing weighing. Because the control panel <NUM> is a separate body, a user can freely dispose the control panel <NUM> at a position easy to operate. However, it does not necessarily have to be configured separately. The control panel <NUM> includes a wired communication function for signal transmission and reception, but may be configured so as to transmit and receive information by wireless communications.

The control panel <NUM> includes, on its upper surface, a display unit <NUM> to display weighing results and states, a switch <NUM> for operation, and an infrared sensor <NUM>. The infrared sensor <NUM> is a switch for opening and closing the opening and closing doors <NUM> and <NUM>, and just by holding a hand over this sensor, the opening and closing doors <NUM> and <NUM> can be automatically opened and closed. A push switch may be provided in place of the infrared sensor <NUM>, or a configuration in which both of the push switch and the infrared sensor <NUM> are provided is also possible. The infrared sensor <NUM> may be provided with a balance operating function other than the function for opening and closing the opening and closing doors <NUM> and <NUM>. A configuration is also possible in which two left and right infrared sensors <NUM> are respectively provided so that each sensor opens and closes a corresponding opening and closing door <NUM>, <NUM>.

The air cylinder <NUM> is a double-acting type, and both of forward and backward strokes of reciprocating motion of a piston inside the air cylinder <NUM> are made by air pressure, so that ports to feed air to the inside of the air cylinder <NUM> are provided at two positions. At the front side of the air cylinder <NUM>, a retreat-side port <NUM> for making the piston move rearward by fed air is provided, and at the rear side, an advance-side port <NUM> for making the piston <NUM> move forward is provided (refer to <FIG>). To these ports <NUM> and <NUM>, air tubes not illustrated are connected, and linked to pressurization pumps 62a and 62b inside the case <NUM> (refer to <FIG>).

Inside the case <NUM>, the pressurization pumps 62a and 62b serving as drive sources of the air cylinder <NUM> and solenoid valves 66a and 66b to control air flowing and stoppage, and a control unit <NUM> to control these, etc., are stored (refer to <FIG>).

Here, the pair of opening and closing doors <NUM> and <NUM> and their opening and closing mechanisms will be described in detail, but since the opening and closing doors <NUM> and <NUM> have the same structure, description will be given of only one opening and closing door <NUM>.

As illustrated in <FIG>, the cylinder box <NUM> is formed of a cylinder storage portion 30f and a cover 30e, and in an inner wall of the cylinder storage portion 30f, a recess is formed to match the shape of the air cylinder <NUM>, and the air cylinder <NUM> is fitted and fixed into this recess. A gap between an upper plate portion of the cover 30e and an upper plate portion of the cylinder storage portion 30f defines a guide groove 30a into which a side edge of the upper surface door <NUM> projects.

As illustrated in <FIG> and <FIG>, the pair of upper frames <NUM> are disposed along concave portions 14a provided at left and right edge portions of an upper portion of the case <NUM>, and constitute frame members of the upper portion of the windshield <NUM>. The cylinder storage portion 30f of the cylinder box <NUM> is configured so that the upper plate portion is placed on an upper surface of the upper frame <NUM>, and as illustrated in <FIG>, a back surface-side end portion is formed into an inverted L shape and its inner side surface comes into contact with a side surface 17b of the upper frame <NUM>, and a right-angle portion of the inverted L shape is engaged with a corner portion of the upper frame <NUM>, and the cylinder storage portion 30f is fixed to the upper frame <NUM>.

The cylinder storage portion 30f does not have a bottom surface (refer to <FIG>), and an upper portion of an outer frame 11b of the opening and closing door <NUM> is disposed to enter the inside of the cylinder storage portion 30f. At a lower end portion of an outer side surface 30b of the cylinder storage portion 30f, an inner flange 30c folded inward is formed over the entire length in a longitudinal direction. In addition, at a lower portion of the outer side surface 17b of the upper frame <NUM>, a projecting portion 17c positioned above the inner flange 30c and extending over the entire length in the longitudinal direction (front-rear direction) is formed. An upper surface of the inner flange 30c and a lower surface of the projecting portion 17c are positioned at substantially the same height.

At front and rear end portions of the upper portion of the outer frame 11b of the opening and closing door <NUM>, engagement portions <NUM> orthogonal to the sliding direction of the opening and closing door <NUM> (the front-rear direction in <FIG> and <FIG>) and projecting in a thickness direction of the opening and closing door <NUM> (the left-right direction in <FIG> and <FIG>) are formed. The engagement portion <NUM> is formed to be supported by respective upper surfaces of the inner flange 30c and the projecting portion 17c, and is formed of a first engagement portion 50a formed to project toward the inner flange 30c side, a second engagement portion 50b formed to project toward the projecting portion 17c side, and further, a third engagement portion 50c formed at a distance below the second engagement portion 50b. The third engagement portion 50c and the second engagement portion 50b are positioned so as to sandwich the projecting portion 17c, and the third engagement portion 50c is positioned corresponding to a guide hole 30d formed of a slit between the inner flange 30c and a portion below the projecting portion 17c, and is positioned at a distance from a lower surface of the projecting portion 17c.

In this way, the opening and closing door <NUM> is suspended by being supported at its upper portion slidably by the upper frame <NUM> serving as a holding portion and the cylinder box <NUM>. A lower end of the opening and closing door <NUM> is disposed at a distance from the surface of the horizontal portion 18a of the guide rail <NUM> formed on the lower frame <NUM>, and the upper portion of the opening and closing door <NUM> is slidable by being guided by the guide hole 30d.

In the present embodiment, the suspending mode of the opening and closing door <NUM> is configured as described above, however, other conventionally known configurations such as a mode in which the engagement portion <NUM> is formed into a T shape and engaged in a slit formed in a flat plate or a mode in which the engagement portion <NUM> is formed into a hook shape and engaged with a projecting rail may also be used.

As illustrated in <FIG>, <FIG>, and <FIG>, on a front end upper surface of the outer frame 11b of the opening and closing door <NUM>, a block-shaped coupling portion 11c is provided, and in the coupling portion 11c, a coupling hole 11d extending in a moving direction of the opening and closing door <NUM> is formed. A tip end of a piston rod 40a extending from the piston inside the air cylinder <NUM> is fitted and fixed into this coupling hole 11d. The piston rod 40a is connected to the outer frame 11b of the opening and closing door <NUM> and the piston rod 40a is moved forward or rearward by air, so that the outer frame 11b slides along the guide hole 30d, and the opening and closing door <NUM> is opened or closed.

In addition, as illustrated in <FIG> and <FIG>, respective lower end surfaces of the outer frames 11b of the respective opening and closing doors <NUM> are positioned at distances from the horizontal portions 18a of the guide rails <NUM>, and are positioned at a height not higher than upper ends of the vertical portions 18b. Therefore, while outside air is reliably prevented from flowing into the weighing chamber S, even if a specimen or dust remains on the horizontal portions 18a, it does not obstruct reciprocating motions of the opening and closing doors <NUM>, and the respective opening and closing doors <NUM> are smoothly reciprocated.

The air cylinder <NUM> is fixed at a distance from the outer frame 11b so as not to come into contact with the upper surface of the outer frame 11b even in the state where the outer frame 11b is engaged with the inner flange 30c (refer to <FIG>), and the air cylinder <NUM> does not obstruct movements of the opening and closing door <NUM>. The coupling portion 11c projects higher than the upper surface of the outer frame 11b, however, the coupling portion 11c is fixed to the tip end of the piston rod 40a, and therefore does not enter below the air cylinder <NUM>, and a movement path of the coupling portion 11c is secured inside the cylinder box <NUM>, so that the cylinder box <NUM> and the coupling portion 11c do not interfere with each other.

The air cylinder <NUM> serving as a driving means of the opening and closing door <NUM> is disposed substantially right above the opening and closing door <NUM> and parallel to the moving direction of the opening and closing door <NUM>. The outer frame 11b of the opening and closing door <NUM> is joined to the air cylinder <NUM> by the coupling portion 11c formed on the upper surface, and the air cylinder <NUM> directly slides the outer frame 11b to move the opening and closing door <NUM>. Therefore, force transmissibility from the air cylinder <NUM> is high, and the opening and closing door <NUM> can be smoothly opened and closed with a small force.

As illustrated in <FIG> and <FIG>, on the horizontal portion 18a of each guide rail <NUM>, a projection <NUM> serving as a restricting member to restrict the lower end of each opening and closing door <NUM> from being displaced in a separating direction from the vertical portion 18b of each guide rail <NUM> is provided along the movement path of each opening and closing door <NUM>. This projection <NUM> has an octagonal prism shape although not clearly illustrated in the drawings. The projection <NUM> is provided so as to be positioned closer to the back surface than the portion joined to the opening and closing door <NUM>, that is, the coupling portion 11c in a state where the piston rod 40a of the air cylinder <NUM> retreats most. By this projection <NUM>, the lower portion of the opening and closing door <NUM> is prevented from wobbling, and smooth movements of the opening and closing door <NUM> are secured. The wobbling prevention is reliably secured in the entire range of movements of the opening and closing door <NUM>.

Moreover, the guide rail <NUM> is formed of the horizontal portion 18a and the vertical portion 18b, and has no groove, so that dust does not accumulate there, and even if dust or a specimen adheres to the guide rail, it can be easily cleaned out, and the projection <NUM> does not serve as an obstruction for this cleaning out.

Subsequently, a driving system of an automatic opening and closing mechanism of the opening and closing door <NUM> will be described with reference to <FIG>. An opening and closing mechanism <NUM> is a mechanism for opening and closing the opening and closing door <NUM>, and each of the left and right opening and closing doors <NUM> includes the opening and closing mechanism <NUM>, and is controlled independently by a connected opening and closing mechanism <NUM>. Each opening and closing mechanism <NUM> is controlled by the control unit <NUM>. In the present embodiment, a pump (first pressurization pump 62a) to move the piston and the piston rod 40a of the air cylinder <NUM> forward (projects out from the air cylinder <NUM>) and a pump (second pressurization pump 62b) to move the piston and the piston rod rearward (retreats into the air cylinder <NUM>) exist separately. <FIG> illustrates only one opening and closing mechanism <NUM>, and the other opening and closing mechanism <NUM> also has the same configuration.

The opening and closing mechanism <NUM> includes the first pressurization pump 62a, the second pressurization pump 62b, a first pressure sensor 64a, a second pressure sensor 64b, the first one-way solenoid valve 66a, the second one-way solenoid valve 66b, the air cylinder <NUM>, and the control unit <NUM>. The air cylinder <NUM> is joined to the coupling portion 11c of the opening and closing door <NUM> through the piston rod 40a.

Both of the first pressurization pump 62a and the second pressurization pump 62b are air pumps. Each pressurization pump 62a, 62b is a drive source of the air cylinder <NUM>, and compresses and feeds air to the air cylinder <NUM>, and projects or retreats the piston and the piston rod 40a by an air pressure to move the opening and closing door <NUM>.

Outlet sides of the first one-way solenoid valve 66a and the second one-way solenoid valve 66b are open to the atmosphere, and air flowing and stoppage are controlled by opening and closing of the valves.

The first pressure sensor 64a monitors a pressure of air discharged from the first pressurization pump 62a, and the second pressure sensor 64b monitors a pressure of air discharged from the second pressurization pump 62b. The two pressure sensors 64a and 64b are respectively connected to the ports <NUM> and <NUM> of the air cylinder <NUM>, and monitor a pressure of air to be supplied to the air cylinder <NUM> and a pressure of air inside the air cylinder <NUM>.

To the advance-side port <NUM> provided at the rear side of the air cylinder <NUM>, the first pressurization pump 62a is connected. The air supply path has a branch halfway, and the first pressure sensor 64a and the first one-way solenoid valve 66a are further connected. To the retreat-side port <NUM> provided at the front side of the air cylinder <NUM>, the second pressurization pump 62b is connected. The air supply path has a branch halfway, and the second pressure sensor 64b and the second one-way solenoid valve 66b are connected to this branch.

The respective components of the opening and closing mechanism <NUM> are disposed inside the case <NUM>, and their operations are controlled by the control unit <NUM>.

Next, operations of the respective components when automatically opening and closing the opening and closing door <NUM> will be described based on <FIG>, but since operations of the respective opening and closing doors <NUM> are the same, description will be given of only one opening and closing door <NUM>.

First, in a "standard state" where a user can manually open and close the opening and closing door <NUM>, neither of the first pressurization pump 62a and the second pressurization pump 62b operates, and the first one-way solenoid valve 66a and the second one-way solenoid valve 66b are open. Because neither of the pressurization pumps 62a and 62b operates, and both one-way solenoid valves 66a and 66b are opened and communicate with the atmosphere, no load is applied from the air cylinder <NUM>, and the opening and closing door <NUM> can be smoothly manually opened and closed.

When a command to "open/close the opening and closing door" is input from the infrared sensor <NUM> on the control panel <NUM>, the control unit <NUM> commands the respective components to operate.

In a case of an "automatic opening operation" to open the opening and closing door <NUM>, that is, when the piston rod 40a of the air cylinder <NUM> is moved rearward, namely, retreated, the second one-way solenoid valve 66b is closed, and pressurization of the second pressurization pump 62b is started. At this time, the first pressurization pump 62a does not operate, and the first one-way solenoid valve 66a is open, so that the piston rod 40a is retreated by an air pressure, and the opening and closing door <NUM> is opened (the state illustrated in <FIG>).

When the opening and closing door <NUM> is fully opened, the air pressure rapidly increases. When this pressure change is detected by the second pressure sensor 64b, pressurization of the second pressurization pump 62b is stopped, the second one-way solenoid valve 66b is opened, and compressed air inside the air cylinder <NUM> is released to the atmosphere, and the mechanism returns to the standard state.

In a case of an "automatic closing operation" to close the opening and closing door <NUM>, that is, when the piston rod 40a inside the air cylinder <NUM> is moved forward, namely, projected out, the first one-way solenoid valve 66a is closed, and pressurization of the first pressurization pump 62a is started. At this time, the second pressurization pump 62b does not operate, and the second one-way solenoid valve 66b is open, so that the piston rod 40a is projected out (moved forward) by an air pressure, and the opening and closing door <NUM> is closed (the state illustrated in <FIG>).

When the opening and closing door <NUM> is fully closed, the air pressure rapidly increases again. When this pressure change is detected by the first pressure sensor 64a, pressurization of the first pressurization pump 62a is stopped, the first one-way solenoid valve 66a is opened, and compressed air inside the air cylinder <NUM> is released to the atmosphere, and the mechanism returns to the standard state.

On the other hand, when calibration of the balance is performed, both of the first one-way solenoid valve 66a and the second one-way solenoid valve 66b are closed. Both one-way solenoid valves 66a and 66b are closed, the piston rod 40a of the air cylinder <NUM> can neither project out nor retreat (can move neither forward nor rearward), and the opening and closing door <NUM> is locked. This is for preventing the opening and closing door <NUM> from being unexpectedly opened or closed during calibration work and influencing the calibration. After the calibration is finished, the first one-way solenoid valve 66a and the second one-way solenoid valve 66b are opened, and the mechanism returns to the standard state.

In this way, the opening and closing door <NUM> is automatically locked during calibration work. A configuration in which the opening and closing door <NUM> is locked in response to a command from the switch <NUM> is also possible. Not only during calibration but also during transportation of the balance <NUM>, by closing both one-way solenoid valves 66a and 66b, the opening and closing door <NUM> can be locked.

As described above, when one pressurization pump operates, the other pressurization pump does not operate, and only one solenoid valve is closed, and the other solenoid valve is opened and communicates with the atmosphere. When the pump that has been operating stops, the closed solenoid valve opens and communicates with the atmosphere. In other words, the configuration is made so that when the pressurization pumps stop, both one-way solenoid valves are opened and communicate with the atmosphere. After the opening and closing door <NUM> is automatically opened or closed, air is released to the atmosphere, the load applied to the opening and closing door <NUM> is eliminated, and it becomes possible to smoothly manually move the opening and closing door <NUM>. While the opening and closing door <NUM> is automatically openable and closable, after it is automatically opened or closed, manual opening/closing becomes possible immediately without any special operation.

Claim 1:
A windshield (<NUM>) for a balance, covering a weighing pan (<NUM>) to define a weighing chamber (S), wherein
the windshield (<NUM>) has a front surface portion (<NUM>), a pair of side surface portions (<NUM>), a back surface portion (<NUM>), and an upper surface portion (<NUM>),
the pair of side surface portions (<NUM>) are respectively opening and closing doors (<NUM>) for opening and closing side surfaces of the weighing chamber (S), upper portions of said opening and closing doors (<NUM>) being supported movably by holding portions (<NUM>,<NUM>) provided along respective side portions of the upper surface portion (<NUM>), and lower portions being guided by guide rails (<NUM>) each formed of a horizontal portion (18a) and a vertical portion (18b), configured to be reciprocated by a driving means (<NUM>), and
on the horizontal portions (18a) of the respective guide rails (<NUM>), restricting members (<NUM>) configured to restrict lower ends of the respective opening and closing doors (<NUM>) from being displaced in separating directions from the vertical portions (18b) of the respective guide rails (<NUM>) are provided along movement paths of the respective opening and closing doors (<NUM>),
characterized in that
the lower ends of the respective opening and closing doors (<NUM>) are positioned at distances from the horizontal portions (18a) of the guide rails (<NUM>), and positioned at a height not higher than upper ends of the vertical portions (18b) .