JPH0861298A - Negative pressure generating unit - Google Patents

Abstract

PURPOSE: To efficiently utilize an amount of compressed air fed from a compressed air feed source and to reduce size and weight. CONSTITUTION: In a negative pressure unit 10, negative pressure operation is generated by an ejector part 16 by means of compressed air introduced through a compressed air feed port 18 and a generated negative pressure is stored at a negative pressure storage part 14. In this case, a control unit controls an amount of compressed air fed to the ejector part 16 through the compressed air feed port 18. Thus, a flow rate of compressed air fed from the compressed air feed source is saved and a negative pressure in the negative pressure storage part 14 is efficiently distributed to an external device by a negative pressure feed part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative pressure generating unit for supplying a negative pressure generated in an ejector section to an external device.

[0002]

2. Description of the Related Art Conventionally, a negative pressure action is generated by an ejector, and a work is attracted and conveyed through a suction means such as a suction pad based on the negative pressure action.

That is, compressed air is supplied from a compressed air supply source to a nozzle constituting an ejector, and compressed air ejected from the nozzle passes through a diffuser,
A negative pressure action is generated between the nozzle and the diffuser. In this case, in order to convey a plurality of works in large quantities and efficiently, a plurality of ejectors are connected in series and integrated, and compressed air from a compressed air supply source is supplied to each of the integrated ejectors. And is using it.

[0004]

However, in the above-mentioned prior art, since the compressed air supply source, for example, the compressed air supply amount in the compressor or the like is limited, it is possible to connect to one compressed air supply source. There is a disadvantage that the number of ejectors is limited. For this reason, when a large number of ejectors are used in excess of the compressed air supply amount in the compressed air supply source, the negative pressure generated in the ejectors decreases, which causes an adverse effect such as suction failure on the work. There is.

Further, in the ejector, in order to generate a negative pressure action, compressed air must be constantly ejected from the nozzle toward the diffuser, and the compressed air passing through the diffuser is exhausted to the atmosphere. Therefore, there is an inconvenience that the compressed air cannot be efficiently used.

Therefore, it is conceivable to increase the number of the compressed air supply sources, but there are other disadvantages such that the cost of the compressed air supply sources is high and a large space is occupied.

In this case, it is conceivable to use a vacuum pump instead of the ejector to suction and convey the work, but similarly, the negative pressure capacity supplied by the vacuum pump is limited, and the vacuum pump is used. There is an inconvenience that the number of pneumatic devices such as adsorption means connected is limited. Also, when trying to accumulate the negative pressure generated using the vacuum pump,
There are disadvantages that the cost of the vacuum pump increases and the size of the entire apparatus increases.

The present invention has been made in order to overcome the above-mentioned inconvenience, and reduces the amount of compressed air supplied from a compressed air supply source so that the compressed air can be efficiently used, and the size and weight can be reduced. It is an object of the present invention to provide a negative pressure generating unit capable of performing the above.

[0009]

To achieve the above object, the present invention provides a block portion connected to a compressed air supply source and having a compressed air supply port, and a compression unit introduced from the compressed air supply port. An ejector unit that generates a negative pressure action by air, a negative pressure storage unit that stores the negative pressure generated in the ejector unit, and a negative pressure supply unit that supplies the negative pressure stored in the negative pressure storage unit to an external device. And a controller unit that controls the amount of compressed air supplied from the compressed air supply port to the ejector unit based on the amount of negative pressure in the negative pressure storage unit.

[0010]

In the negative pressure generating unit according to the present invention, the negative pressure is generated in the ejector section by the compressed air introduced from the compressed air supply port, and the generated negative pressure is stored in the negative pressure storage section. The controller unit detects a negative pressure amount in the negative pressure storage unit and supplies compressed air to the ejector unit until the negative pressure amount reaches a predetermined value. When the amount of negative pressure in the negative pressure storage unit reaches a predetermined value, the controller unit stops the supply of compressed air to the ejector unit.

In this case, the controller unit supplies compressed air to the ejector unit so that the negative pressure amount in the negative pressure storage unit satisfies a predetermined value, or stops the compressed air to control the amount of compressed air supplied. Therefore, the flow rate of the compressed air supplied from the compressed air supply source can be reduced, and the negative pressure supply section can efficiently distribute the negative pressure in the negative pressure storage section to the external device.

[0012]

Preferred embodiments of the negative pressure generating unit according to the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a front view of a negative pressure generating unit according to an embodiment of the present invention, FIG. 2 is a plan view of FIG. 1, and FIG.
3 is a vertical sectional view taken along line III-III, FIG. 4 is a right side view of FIG. 1, and FIG. 5 is a rear view of FIG.

As shown in FIG. 3, this negative pressure generating unit 10 is basically a base plate 12 and a negative pressure storage that is provided on the base plate 12 and stores the generated negative pressure. Section 14, an ejector section 16 formed integrally with the negative pressure storage section 14 and comprising a plurality of nozzle sections, and a tube provided with the negative pressure storage section 14 and the ejector section 16 and having a compressed air supply port 18. A negative pressure detection unit 24 that is mounted on the block unit 22 provided with the joint 20 and the ejector unit 16 and detects the negative pressure in the negative pressure storage unit 14.
Fixed on the base plate 12, and a muffling section 26 disposed adjacent to the negative pressure detecting section 24 for discharging compressed air derived from the ejector section 16 to the outside and exhibiting a muffling function. The negative pressure supply unit 28 (see FIG. 2) for supplying a negative pressure to the suction means such as the suction pad, and the negative pressure storage unit 14 and the negative pressure supply unit 28 are provided adjacent to each other, and the lead wire 30 is provided therebetween. Negative pressure detection unit 24 and negative pressure supply unit 28
Controller unit 32 into which the detection signal from
(See FIG. 2).

On the upper surface of the block portion 22, there is provided the pipe joint 20 connected to the compressed air supply source 34 (see FIG. 6) via a tube or the like. A supply valve 36 and a destruction source valve 38 are attached to one side surface portion of the block portion 22, and the respective input ports of the supply valve 36 and the destruction source valve 38 are respectively provided with compressed air supply ports of the pipe joint 20 via passages 40. It is formed so as to communicate with 18 (see FIG. 3). The supply valve 36 and the destruction source valve 38 are the controller unit 32.
The position state of the valve element is switched and controlled based on the electric signal derived from the. The output port of the supply valve 36 is formed so as to communicate with a first nozzle portion 42 and a second nozzle portion 44, which will be described later, via a branch passage defined in the block portion 22. Further, the block portion 22
The first communication passage 46 and the second communication passage 46 communicating with the negative pressure supply unit 28.
A communication passage 48 is defined.

The negative pressure storage unit 14 comprises a negative pressure storage tank 52 having a negative pressure storage chamber 50 for storing the negative pressure generated in the ejector unit 16, and the negative pressure storage tank 52 includes:
First to third passages 54, 56, 58 communicating with negative pressure generating chambers (described later) of the ejector portion 16 are defined.
The opening of the first to third passages 54, 56, 58 has a first
-Third check valves 60, 62, 64 are provided respectively, and by opening the first-third check valves 60, 62, 64, the negative pressure storage chamber 50 in the negative pressure storage tank 52 is opened.
And the negative pressure generating chamber in the ejector unit 16 communicate with each other. The negative pressure storage tank 52 can be formed by extrusion molding.

The ejector portion 16 is formed by a multi-stage ejector, and includes an ejector body 66 and the ejector body 6 described above.
First to fifth nozzle portions 42, 44, 68, 70, which are fixed in the nozzle 6 and each include a nozzle and a diffuser.
72 and 72. In this case, the first to fifth nozzle portions 4
2, 44, 68, 70 and 72 are provided with nozzles each having a nozzle diameter that is gradually tapered and then gradually expanded, and each nozzle hole is formed with a predetermined diameter. ing. The first to fifth nozzle parts 42, 44, 68, 7
0, 72, the first nozzle portion 42 and the second nozzle portion 4
4 communicates with the passages 40 defined in the block portion 22, and the first nozzle portion 42 and the second nozzle portion 4 respectively.
It is arranged so that the flow paths of the compressed air flowing through 4 are parallel to each other. A first negative pressure generating chamber 76 is defined between the nozzle hole of the first nozzle portion 42 and the diffuser 74, and the first passage 54 is opened when the first check valve 60 is opened.
The first negative pressure generating chamber 76 and the negative pressure storage chamber 50 are formed to communicate with each other via the. A passage 80 communicating with the second negative pressure generating chamber 78 is defined at the end of the diffuser 74.

A through hole 82 is defined in the ejector body 66 located above the first nozzle portion 42, and the second to fifth nozzle portions 44, 68, 70, 7 are formed in the through hole 82.
2 are arranged in a straight line. Second nozzle portion 44
Is a nozzle having a nozzle hole, and the third to fifth nozzle portions 68, 70, 72 are integrally formed with a nozzle 84.
Consists of A second negative pressure generating chamber 78 is defined between the second nozzle portion 44 and the third nozzle portion 68, and the second negative pressure generating chamber 78 is, as described above, the first nozzle portion 4.
It communicates with the second passage 80. A third negative pressure generating chamber 88 that exerts a suction action through the first suction hole 86 is defined between the third nozzle portion 68 and the fourth nozzle portion 70, and the second check valve 62 is further provided. Under the opening action of the second passage 56
The third negative pressure generating chamber 88 and the negative pressure storage chamber 50 are formed to communicate with each other via the. A fourth negative pressure generating chamber 92 that exerts a suction action through the second suction hole 90 is defined between the fourth nozzle unit 70 and the fifth nozzle unit 72, and the third check valve 64 is further provided. The fourth negative pressure generating chamber 92 and the negative pressure storage chamber 50 are formed to communicate with each other via the third passage 58 under the opening action of the above. The third to fifth nozzle portions 6
It is preferable that the nozzles 84 forming 8, 70, 72 are integrally formed by a casting method using a material such as aluminum. In addition, the third to fifth nozzle portions 68, 70, 7
2 also uses the function of the diffuser for each of the nozzles in the previous stage. For example, the third nozzle portion 68 has a function as a nozzle, and also has a function as a diffuser for the second nozzle portion 44.

At the end of the through hole 82 in the ejector body 66, there are provided a first silencer 96 and a second silencer 98 which constitute the sound deadening portion 26 and are surrounded by the cover member 94. A slit 100 is defined on the upper surface of the cover member 94, and the compressed air flowing out of the ejector unit 16 through the slit 100 is exhausted to the outside.

A negative pressure detector 24 adjacent to the muffler 26.
Is a switch 10 including a semiconductor pressure sensor 102.
4, the switch 104 controls the controller unit 3 when the negative pressure in the negative pressure storage chamber 50 introduced through the passage 106 reaches a preset negative pressure.
It carries out the function of deriving a signal in 2.

The negative pressure supply unit 28 is composed of first to eighth supply mechanisms 108a to 108h, each of which is composed of substantially the same element. The first supply mechanism 108a is a self-holding type which controls the opening / closing position of the main valve 110. It is composed of a pilot valve 112, a breakage supply valve 114, a suction filter 116, and a switch 118 (see FIG. 6). In this case, the second to eighth supply mechanisms 108b to 108h are configured substantially the same as the first supply mechanism 108a, and thus detailed description thereof will be omitted. The pilot valve 112, the breakage supply valve 11
4 and the switch 118 are respectively connected to the controller unit 32 via the lead wire 30, and the pilot valve 112 and the breakage supply valve 114 are controlled to switch the position state of the valve element based on an electric signal derived from the controller unit 32. Then, the switch 118 has a function of detecting whether or not the suction pad 120 has surely suctioned the work W under the negative pressure. The suction pad 120 that constitutes an external device is connected to the negative pressure port 122 (see FIG. 5) of the first to eighth supply mechanisms 108a to 108h via a tube (not shown). In this embodiment, the negative pressure supply unit 28 is connected to the first to eighth supply mechanisms 108a to 1a.
Although it is described by 08h, it is needless to say that the number is not limited to eight. 5 and 6, reference numeral 124 indicates an exhaust port,
The exhaust port 124 is provided for each of the supply mechanisms 108a to 108h.
Performs the function of exhausting the compressed air remaining inside.

The controller unit 32 is composed of a CPU unit, an input / output unit, an I / O unit, a communication unit, a power supply unit, etc., which are not shown, and the pilot valve 112 and the breakage supply valve electrically connected by the lead wires 30, respectively. It is possible to serially transmit an electrical signal to 114, or distributed processing network communication such as a local area network (LAN) or a local operating network (LON), or it is possible to save wiring by a spread spectrum communication means. . The controller unit 32
Is an input means 12 such as a compressed air supply source 34 and a keyboard.
6, and a display means 128 such as a CRT is electrically connected. The operator detects the negative pressure state in the negative pressure storage tank 52 via the input means 126.
4 can be set and changed to a predetermined negative pressure value, and
The switch 11 that is connected close to the suction pad 120
Display means 128 based on the electrical signal derived from 8
It is possible to visually confirm the suction state of the work W through the.

Negative pressure generating unit 1 according to an embodiment of the present invention
0 is basically configured as described above,
Next, the operation and effects will be described based on the pneumatic circuit shown in FIG.

First, an electric signal is derived from the controller unit 32 to the compressed air supply source 34, the compressed air supply source 34 is driven, and compressed air is introduced from the compressed air supply port 18. The compressed air passes through the passage 40 in the block portion 22.
It reaches the input ports of the breakage source valve 38 and the supply valve 36 via and is branched from the passage 40 and introduced into the first communication passage 46. At this time, the controller unit 3
The electric signal is derived from 2 to the supply valve 36,
By switching the valve position of from the closed state to the open state,
The compressed air is supplied to the first nozzle portion 42 and the second nozzle portion 44 of the ejector portion 16 via the passage 40.

The compressed air supplied to the first nozzle portion 42 and ejected from the nozzle holes passes through the diffuser 74 and is defined between the second nozzle portion 44 and the third nozzle portion 68 via the passage 80. It is introduced into the second negative pressure generating chamber 78. When the compressed air passes through the diffuser 74, a negative pressure action is generated in the first negative pressure generation chamber 76, and the negative pressure action causes the first negative pressure action to occur.
The check valve 60 is opened. As a result, the first negative pressure generation chamber 76 and the negative pressure storage chamber 50 communicate with each other through the passage 80, and a negative pressure of a predetermined pressure is accumulated in the negative pressure storage chamber 50.
The negative pressure storage chamber 50 in the negative pressure storage tank 52 is assumed to be at atmospheric pressure in advance.

On the other hand, when the compressed air introduced into the second nozzle portion 44 reaches the third nozzle portion 68, the second compressed air is formed between the second nozzle portion 44 and the third nozzle portion 68. A negative pressure action is generated in the negative pressure generation chamber 78. In this case, the third
The nozzle portion 68 functions as a diffuser for the second nozzle portion 44. Due to the negative pressure action generated in the second negative pressure generating chamber 78, the pressure fluid drawn from the first nozzle portion 42 is forcibly sucked through the passage 80.

Next, the compressed air introduced from the third nozzle portion 68 is led out to the fourth nozzle portion 70, and at this time, it is defined between the third nozzle portion 68 and the fourth nozzle portion 70. A negative pressure action is generated in the third negative pressure generation chamber 88. The second check valve 62 is opened by this negative pressure action, and the third negative pressure generating chamber 88 and the negative pressure storage chamber 5 are passed through the second passage 56.
It communicates with 0. As a result, a negative pressure of a predetermined pressure is accumulated in the negative pressure storage chamber 50.

Subsequently, the compressed air introduced from the fourth nozzle portion 70 is led out to the fifth nozzle portion 72, and at this time, it is defined between the fourth nozzle portion 70 and the fifth nozzle portion 72. A negative pressure action is generated in the fourth negative pressure generation chamber 92. Due to this negative pressure action, the third check valve 64 is opened, and the fourth negative pressure generating chamber 92 and the negative pressure storage chamber 50 are passed through the passage 58.
Communicates with. As a result, a negative pressure of a predetermined pressure is accumulated in the negative pressure storage chamber 50.

The compressed air led out from the fifth nozzle portion 72 is silenced when passing through the first silencer 96 and the second silencer 98 constituting the silencer portion 26, and is exhausted to the outside from the slit 100 of the cover member 94. To be done.

The magnitude of the negative pressure generated at this time is determined by the correlation between the diameter of each nozzle hole and the diameter of the diffuser (nozzle portion in the subsequent stage), and the first negative pressure generating chamber 76> the second negative pressure generating> The chamber 78> the third negative pressure generating chamber 88> the fourth negative pressure generating chamber 92 becomes the first to fourth negative pressure generating chambers 76, 78,
The order of the check valves that open according to the negative pressures of 88 and 92 is also the first check valve 60, the second check valve 62, and the third
The check valves 64 are operated in this order.

As described above, the first to third check valves 60,
By the opening operation of 62, 64, the passages 54, 56,
A negative pressure is supplied to the negative pressure storage tank 52, which was in the atmospheric pressure state, through 58, and a predetermined amount of negative pressure is stored in the negative pressure storage chamber 50. The negative pressure value stored in the negative pressure storage tank 52 is detected by the semiconductor pressure sensor 102 of the switch 104 to which the negative pressure is introduced via the passage 106. The switch 104 sends an electric signal to the controller unit 32 when a preset negative pressure value is reached.
On the other hand, the controller unit 32 outputs an electric signal to the supply valve 36 to switch the valve position of the supply valve 36 from the open state to the closed state.

In this way, the supply valve 36 is switched to the closed state, so that the supply of the compressed air to the ejector section 16 is stopped. Therefore, the first to third check valves 6 are
0, 62, 64 are closed in the order of the third check valve 64, the second check valve 62, and the first check valve 60.
Therefore, the passages 54, 5 communicating with the negative pressure storage chamber 50 are generated by closing the first to third check valves 60, 62, 64.
6 and 58 are closed, and the negative pressure in the negative pressure storage tank 52 is maintained at a predetermined negative pressure value. The controller unit 32 derives an electric signal to the compressed air supply source 34 after detecting that the electric pressure is introduced from the switch 104 and the negative pressure in the negative pressure storage tank 52 has reached a predetermined value. The supply of compressed air to the compressed air supply port 18 is stopped.

After the negative pressure of a predetermined pressure is stored in the negative pressure storage tank 52 as described above, the controller unit 3
2 outputs an electric signal to each pilot valve 112 of the 1st-8th supply mechanisms 108a-108h, and switches the valve position of each pilot valve 112 from a closed state to an open state. In this case, the pit valve 112 is formed to communicate with the compressed air supply port 18 via the first communication passage 46,
The compressed air supplied from the compressed air supply port 18 has already reached the input port of the pilot valve 112. Therefore, the compressed air introduced through the opened pilot valve 112 switches the valve position of the main valve 110 from the closed state to the open state. As a result, a negative pressure is supplied from the negative pressure storage tank 52 to the suction pad 120 through the main valve 110, and the work W is sucked and conveyed based on this negative pressure action. It should be noted that whether or not the work W is surely adsorbed to the adsorption pad 120 can be confirmed based on a detection signal derived from the switch 118 to the controller unit 32.

Next, a case will be described in which the work W sucked and held by the suction pad 120 is conveyed to a predetermined position and separated.

An electric signal is derived from the controller unit 32 to each pilot valve 112, and each pilot valve 112
The valve position of is switched from the open state to the closed state. As a result,
Since the pilot pressure is not supplied from each pilot valve 112 to the main valve 110, the main valve 110 is switched from the open state to the closed state, and the supply of the negative pressure to the suction pad 120 is stopped. On the other hand, the controller unit 32 outputs an electric signal to the destruction source valve 38 and each of the destruction supply valves 114 constituting the first to eighth supply mechanisms 108a to 18h, so that the valve position of the destruction source valve 38 is closed. The state is switched to the open state, and the valve position of the breakage supply valve 114 is switched from the closed state to the open state. As a result, the compressed air introduced from the compressed air supply port 18 becomes
8 and the suction pad 12 through each break supply valve 114
0, the negative pressure state is released, and the work W is separated from the suction pad 120.

When the negative pressure amount in the negative pressure storage tank 52 is reduced by supplying a negative pressure to the external equipment such as the suction pad 120, the controller unit 32 sends an electric signal to the compressed air supply source 34. To supply compressed air to the compressed air supply port 18 and supply valve 36
By supplying the compressed air to the ejector unit 16 by switching the valve position of No. 2, it is possible to store a negative pressure of a predetermined pressure in the negative pressure storage tank 52 by the above-mentioned operation.

As described above, in the negative pressure generating unit 10 according to this embodiment, after the negative pressure of the predetermined value is stored in the negative pressure storage tank 52 without constantly supplying the compressed air to the ejector section 16. The supply of compressed air to the ejector unit 16 is stopped. Therefore, compared with the prior art in which the compressed air is constantly supplied to the ejector and the compressed air is constantly ejected from the nozzle to generate a negative pressure action between the nozzle and the diffuser, the negative pressure according to the present embodiment is reduced. In the generation unit 10, the amount of compressed air supplied from the compressed air supply source 34 can be saved, and the supplied compressed air can be used efficiently.

Further, the negative pressure of the predetermined value accumulated in the negative pressure storage tank 52 can be efficiently distributed to a plurality of external devices and the like under the control action of the controller unit 32 by the pilot valve 112.

Further, in the negative pressure generating unit 10 according to this embodiment, the ejector section 16 for generating a negative pressure, the negative pressure storage section 14 for storing the generated negative pressure, and the negative pressure storage section 1 are provided.
4, the negative pressure supply unit 28 for supplying negative pressure to various external devices is unitized, and the controller unit 32
By reducing the wiring through the, it is possible to manufacture the device in a small size and a light weight, and to effectively use the space.

Furthermore, as compared with the case where the vacuum pump is provided with negative pressure storage means, the negative pressure generating unit 10 according to the present embodiment can be made smaller and lighter, and the negative pressure in the ejector section 16 can be reduced. There is an advantage that the negative pressure can be stored in the negative pressure storage tank 52 quickly by shortening the pressure generation time.

[0041]

According to the negative pressure generating unit of the present invention, the following effects can be obtained.

That is, since the flow rate of the compressed air introduced into the ejector section can be controlled via the controller unit, the flow rate of the compressed air supplied from the compressed air supply source can be saved.

Further, the negative pressure generated in the ejector section is stored in the negative pressure storage section, and the stored negative pressure is efficiently supplied to the external device through the negative pressure supply section under the control of the controller unit. It becomes possible.

Further, an ejector section for generating a negative pressure, a negative pressure storage section for storing the generated negative pressure, a negative pressure supply section for supplying the negative pressure from the negative pressure storage section to various external devices are unitized. In addition, since the wiring is reduced through the controller unit, the negative pressure generating unit can be manufactured in a small size and light weight, and the space can be effectively used.

[Brief description of drawings]

FIG. 1 is a front view of a negative pressure generating unit according to an embodiment of the present invention.

FIG. 2 is a plan view of the negative pressure generating unit shown in FIG.

3 is a vertical cross-sectional view taken along the line III-III shown in FIG.

FIG. 4 is a right side view of the negative pressure generating unit shown in FIG.

5 is a rear view of the negative pressure generating unit shown in FIG.

FIG. 6 is a pneumatic circuit diagram showing an operation of the negative pressure generating unit shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Negative pressure generation unit 12 ... Base plate 14 ... Negative pressure storage part 16 ... Ejector part 18 ... Compressed air supply port 22 ... Block part 24 ... Negative pressure detection part 26 ... Muffling part 28 ... Negative pressure supply part 30 ... Lead Line 32 ... Controller unit 34 ... Compressed air supply source 36 ... Supply valve 38 ... Breakage source valve 40, 54, 56, 58 ... Passage 42, 44, 68, 70, 72 ... Nozzle part 46, 48 ... Communication passage 50 ... Negative Pressure storage chamber 52 ... Negative pressure storage tank 60, 62, 6
4 ... Check valve 76, 78, 88, 92 ... Negative pressure generating chamber 104, 118
... Switches 108a to 108h ... Supply mechanism 110 ... Main valve 112 ... Pilot valve 114 ... Rate supply valve 116 ... Suction filter 120 ... Suction pad W ... Work

Claims (5)

[Claims] 1. A block unit connected to a compressed air supply source and having a compressed air supply port, an ejector unit for generating a negative pressure action by compressed air introduced from the compressed air supply port, and an ejector unit. A negative pressure storage unit that stores the negative pressure stored therein, a negative pressure supply unit that supplies the negative pressure stored in the negative pressure storage unit to an external device, and the compression based on the negative pressure amount in the negative pressure storage unit. A negative pressure generating unit, comprising: a controller unit that controls the amount of compressed air supplied from the air supply port to the ejector unit. 2. The negative pressure generating unit according to claim 1, wherein the ejector portion is formed by a multistage ejector including a plurality of nozzle portions. 3. The unit according to claim 1, wherein the block section includes a supply valve interposed between the compressed air supply port and the ejector section, and the supply valve is based on an electric signal derived from the controller unit. The negative pressure generating unit is characterized in that the valve position is switched. 4. The unit according to claim 1, wherein the negative pressure supply unit is composed of a plurality of supply mechanisms connected in series, and each of the supply mechanisms is urged by a pilot valve and pilot pressure of the pilot valve. In this case, the negative pressure generating unit includes a main valve that supplies negative pressure to an external device through a passage communicating with the negative pressure storage unit. 5. The unit according to claim 1, wherein the external device comprises a suction pad, and the workpiece sucked and conveyed to the suction pad by the negative pressure supplied from the negative pressure supply unit is transferred from the suction pad. A negative pressure generating unit comprising negative pressure releasing means for releasing the negative pressure.