JP2016175150A - Slope stand for article pick-up and article pick-up method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slope structure that is suitable for picking up a small article, and an article pick-up method using the slope structure.SOLUTION: A slope stand 20 for article pick-up has a slope 21 comprising a non-magnetic material and a magnet 25 embedded to the slope. In the magnet, an end surface 26 of a slope side is a first magnetic pole. Also, an article pick-up method has the steps of: making an article fall to the upper part of the slope of the slope stand; making the magnet attract and stop the article sliding down on the slope; bringing a sleeve into abutment with the stopped article while a magnet unit is retracted by using a holding device where the magnet unit, in which a first magnetic pole is formed in the front end surface, is capable of linear motion in the sleeve; advancing the magnet unit and making the article attract to the holding device; and separating the entire of the holding device from the slope.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a slope base for picking up a minute article, and a method for picking up an article using the slope base.

  In recent years, the use of minute parts has increased due to the downsizing of electronic devices and the like and the precision of various mechanical devices. For handling these minute parts, many devices that attract and hold the parts by magnetic force are used. For example, Patent Documents 1 to 3 describe apparatuses that hold an article by magnetism. An apparatus using magnetic attraction can hold articles of relatively various shapes, although the material of the article that can be adsorbed is limited. In addition, with the development of high-performance magnets, the types of materials that can be adsorbed are increasing.

JP 2008-188747 A JP 2006-150529 A JP-A-6-099387

  When holding a piece-like or plate-like article using such a holding device, the posture of the article at the time of adsorption can be stabilized by adsorbing the magnet to either the front or back main surface of the article. However, depending on the convenience of the process, a piece-like or plate-like article may be supplied in a “standing” posture, that is, in a posture in which the main surface is vertical. When many articles are arranged close to each other, it is difficult to bring the holding device closer to the main surface from the side of the article, and it is difficult to pick up the article directly.

  In such a case, the article can be once grasped with a parallel clamp or the like and placed in a “sleeping” state on the table, and taken up again by the holding device. However, in order to place an article on a table using a parallel clamp, a complicated operation is required.

  The present invention has been made in consideration of the above, and an object thereof is to provide a slope structure suitable for picking up a minute article. Moreover, it is providing the picking-up method of the articles | goods using the slope structure.

  The slope base of the present invention has a slope made of a non-magnetic material and a magnet embedded in the slope, and the end face on the slope side of the magnet is the first magnetic pole. Here, the first magnetic pole is an N pole or an S pole.

  Preferably, the inclined surface has a first portion whose inclination decreases downward, and a second portion that is smoothly continuous from the lower end of the first portion and has a constant inclination, and the magnet is the first portion. Embedded in two parts.

  Preferably, the magnet is an Nd-Fe-B magnet. Preferably, the magnetic flux density on the surface of the slope by the magnet is 300 mT or more.

  The article picking method of the present invention uses any one of the above-described slope base and holding device. The holding device includes a magnet unit that is configured by one permanent magnet or a combination of a plurality of magnetic members including at least one permanent magnet, and has a first magnetic pole formed on a front end surface thereof, and the magnet unit is a sleeve. It is a holding device that can move linearly inside. The article picking method according to the present invention includes a step of dropping an article on an upper portion of the slope, a step of attracting the article sliding down the slope and causing the magnet to stand still, and the sleeve with the magnet unit retracted. A step of abutting the stationary article; a step of advancing the magnet unit to attract the article to the holding device; and a step of pulling the entire holding device away from the slope.

  Here, the front means a direction in which the article to be held is viewed from the holding device, and the rear means the opposite direction. Moving the magnet unit forward is said to move forward, and moving backward is said to move backward. The magnetic member is a member made of a magnetic material, and the magnetic material is a concept including a permanent magnet and a soft magnetic material.

  Preferably, the holding device has an annular shape or a cylindrical shape in which a foremost member among the members constituting the magnet unit has a hole penetrating in the axial direction of the sleeve. Alternatively, preferably, in the holding device, at least a central portion of a front end surface of the magnet unit is a spherical surface convex forward.

  Preferably, in the holding device, a member located in the forefront among members constituting the magnet unit is a permanent magnet.

  Preferably, in the holding device, the permanent magnet is an Nd—Fe—B magnet. Preferably, the holding device has a magnetic flux density of 300 mT or more at a front end surface of the magnet unit.

  According to the slope base or the article picking method of the present invention, a minute article can be easily taken up using a simple structure.

It is a perspective view of the slope for goods collection of one embodiment of the present invention. It is sectional drawing of the slope stand for goods collection of one Embodiment of this invention. It is a structural diagram of one holding device used for the article picking method of the present invention. It is a figure which shows the article picking method of this invention. It is a structural diagram of another holding device used for the article picking method of the present invention. It is a figure which shows the modification of a structure of the magnet unit of a holding | maintenance apparatus. It is a figure for demonstrating the positioning mechanism of the articles | goods with a hole. It is a structural diagram of another holding device used for the article picking method of the present invention.

  An embodiment of the slope table for collecting articles according to the present invention will be described with reference to FIGS. 1 and 2.

  1 and 2, the slope base 20 has a slope 21 and a magnet 25 embedded in the slope. The inclined surface 21 includes a first portion 22 whose inclination decreases downward, and a second portion 23 that is smoothly continuous from the lower end of the first portion and has a constant inclination. The magnet 25 is embedded in the second part. When the article to be picked up is dropped from the upper part of the slope, the article slides down the slope and is attracted to the magnet and stopped, so that it can be picked up by a separately prepared holding device.

  The slope 21 is made of a nonmagnetic material. As the nonmagnetic material, plastic or wood is preferably used. This is because when the article is dropped, the article is hardly damaged.

  The size of the slope is not particularly limited, but a preferable range is defined by the size of the article to be picked up. If the article is too large for the magnet, the article cannot be stationary with the magnet. In consideration of the size of an article to which the slope base of the present embodiment can be suitably applied, the width of the slope is preferably 100 mm or less, more preferably 50 mm or less. In addition, if the slope is too small, it is difficult to manufacture the slope base, and therefore the width of the slope is preferably 2 mm or more, more preferably 5 mm or more. The length of the slope is preferably shorter in order to suppress the acceleration of the article. The length of the slope is not less than the size of the article and may be slightly larger than the size of the article. In consideration of the size of the article to which the slope base of the present embodiment can be suitably applied, the length of the slope is preferably 100 mm or less, more preferably 50 mm or less, preferably 2 mm or more, more preferably 5 mm or more. is there.

  In addition, the slope 21 of the present embodiment has the second portion 23 having a constant inclination, but the present invention is not limited to this, and the entire slope is composed of only the first portion 22 whose inclination decreases downward. May be. In addition, if the inclination of the place where the article is dropped is too small, the article may jump on the slope and may not slide down smoothly. Therefore, the slope at the top of the slope is preferably 70 degrees or more, more preferably 80 degrees or more.

  If the slope 21 is too inclined, it will be difficult to attract and stop the article with a magnet. Therefore, the inclination of the slope is preferably 60 degrees or less, more preferably 50 degrees or less at the position where the magnet 25 is embedded. In order to sufficiently slow down the article, it is preferable that the inclination of the position where the magnet is embedded is small. However, in that case, the entire length of the slope becomes longer and the installation space for the slope base becomes larger. From this point, the inclination of the slope is preferably 15 degrees or more, more preferably 30 degrees or more, at the position where the magnet 25 is embedded.

  The magnet 25 of this embodiment is a permanent magnet. It is preferable to use a magnet having a strong magnetic force. This is because an article made of a greater variety of materials can be adsorbed and stopped. The magnet is preferably a Nd—Fe—B magnet (neodymium magnet). Alternatively, regardless of the type of magnet, the magnetic flux density on the inclined surface by the magnet is preferably 300 mT or more, more preferably 400 mT or more, and particularly preferably 500 mT or more. As a result, austenitic stainless steel that is not adsorbed by general magnets and articles made of many alloys containing iron, cobalt, nickel, chromium, manganese, and the like as components can be adsorbed and stopped. From the viewpoint of availability, the magnetic flux density of the magnet is preferably 700 mT or less.

  The magnet 25 has an internal magnetization direction substantially orthogonal to the inclined surface 21, the end surface 26 on the inclined surface side is the first magnetic pole (for example, N pole), and the opposite end surface 27 inside the inclined base is the second magnetic pole. (For example, S pole). By forming the magnetic pole so as to face the slope in this way, the magnetic flux density on the slope surface can be increased.

  The magnet 25 may have the slope-side end face 26 exposed to the slope 21. At this time, the slope-side end surface may be slightly recessed from the slope. On the other hand, the magnet may be covered with a film or sheet attached to the entire slope. Thereby, an article | item can slip down smoothly, without being caught in the recessed part with which the magnet was embedded. As a sheet covering the magnet, for example, a polytetrafluoroethylene sheet having a thickness of 1 mm can be suitably used.

  In addition, you may provide the guide wall (not shown) in which the width | variety on either side narrows toward the downstream on the both sides of a slope so that articles | goods may slide down to the upper part of the magnet 25 uniformly. As a result, the article that has been slid can be accurately guided to the center of the magnet 25. A stop member using an elastic body made of rubber or resin may be provided at the end of the slope in preparation for the case where the article is not stopped by the magnet.

  Next, a first embodiment of a holding device used for picking up articles will be described with reference to FIG.

  In FIG. 3, the holding device 10 includes a sleeve 30, an air cylinder 35, and a magnet unit 40. The sleeve has an opening 32 at the front (lower side in FIG. 3) end. In the air cylinder, a main body 36 is fixed to the sleeve via a flange 38, and a movable rod 37 is accommodated in the sleeve. The magnet unit is fixed to the tip of the movable rod of the air cylinder. When the air cylinder extends, the magnet unit moves forward, and the article can be adsorbed at the opening.

  The sleeve 30 is made of a nonmagnetic material. As the nonmagnetic material, plastic, copper, aluminum or the like can be used. Among these, it is preferable to use plastic. This is because when the open end 31 of the sleeve comes into contact with the article, the article is hardly damaged.

  Further, the sleeve opening end 31 may be provided with a non-slip portion in order to suppress the displacement of the article. The anti-slip portion can be formed, for example, by sticking an elastic sheet made of rubber or resin having a thickness of about 0.1 mm to 0.3 mm to the opening end 31.

  The shape of the sleeve 30 is not particularly limited, but is preferably a cylindrical shape. This is because the outer diameter can be minimized for the same cross-sectional area.

  The air cylinder 35 has a main body 36 fixed to the sleeve 30 via a flange 38. As a method for fixing the air cylinder to the flange and a method for fixing the sleeve, a known method such as screwing can be used. Further, the air cylinder body may be directly fixed to the sleeve without using the flange. Since the main body 36 is fixed to the sleeve, when the air cylinder expands and contracts, the movable rod 37 accommodated in the sleeve can linearly move in the axial direction relative to the sleeve.

  The air cylinder 35 is a kind of linear actuator. A linear actuator is a device that converts various types of energy into linear motion. As the linear actuator, in addition to an air cylinder, a hydraulic cylinder, an electric cylinder, a linear motor, or a motor that converts a rotational motion of the motor into a linear motion by a motion conversion mechanism can be used. Among these, it is preferable to use an air cylinder because it can be miniaturized and accurate control is easy.

  The magnet unit 40 is fixed to the tip of the movable rod 37. Thereby, when the air cylinder 35 expands and contracts, the magnet unit is guided to the inner surface of the sleeve 30 along with the linear motion of the movable rod, and linearly moves in the axial direction of the sleeve.

  The magnet unit 40 is composed of a single permanent magnet 50 in this embodiment. The front end face 47 of the magnet unit is a first magnetic pole (for example, N pole) of the same type as the slope end face (26 in FIG. 2) of the magnet embedded in the slope base, and the rear end face 48 on the opposite side is the second magnetic pole ( For example, S pole). By forming the magnetic pole so as to face the opening 32 in this way, the magnetic flux density emitted from the front end surface of the magnet unit is increased, and a strong attracting force is obtained.

  The magnet unit may be constituted by a combination of a plurality of magnetic members including at least one permanent magnet. Other configuration examples of the magnet unit will be described later.

  As the permanent magnet 50, it is preferable to use a magnet having a strong magnetic force. This is because articles made of more various materials can be adsorbed. The permanent magnet is preferably a Nd—Fe—B based magnet (neodymium magnet). Or the magnetic flux density in the front end surface 47 of the magnet unit 40 becomes like this. Preferably it is 300 mT or more, More preferably, it is 400 mT or more, Especially preferably, it is 500 mT or more irrespective of the kind of permanent magnet. This makes it possible to adsorb articles made of austenitic stainless steel that is not adsorbed by general magnets and articles made of many alloys containing iron, cobalt, nickel, chromium, manganese, and the like as components. Moreover, a micro article | item can be conveyed at high speed by hold | maintaining strongly with a strong magnetic force. From the viewpoint of easy availability, the magnetic flux density of the permanent magnet is preferably 700 mT or less.

  Next, a method for picking up an article using the slope and the holding device of this embodiment will be described with reference to FIG.

  In FIG. 4A, the article 90 is picked up by a parallel clamp 70 or the like from a pallet or the like (not shown), moved above the slope 21 and dropped. The article slides down the slope by its own weight (FIG. 4B), is attracted by the magnet 25, and stops in the middle of the slope (FIG. 4C).

  Next, in FIG. 4D, the holding device 10 is directly opposed to the article 90 with the magnet unit 40 retracted, and the open end 31 of the sleeve 30 is brought into contact with the article. When the holding device is operated by a robot arm or the like, an accurate operation is possible by adjusting the posture and position of the holding device while checking the position of the article with a camera.

  Next, in FIG. 4E, the air cylinder is extended, the movable rod 37 and the magnet unit 40 are advanced, and the article is attracted to the holding device.

  Next, in FIG. 4F, the entire holding device 10 is pulled away from the slope while holding the article 90. As described above, the article could be taken up.

  What is important here is that both the magnet embedded in the slope and the magnet unit of the attracting device are magnetized in opposite directions, the end face 26 on the slope side of the magnet 25 and the front of the magnet unit 40. Both end faces 47 are first magnetic poles (N poles in FIG. 4). Accordingly, in FIG. 4E, the article 90 and the magnet 25 attracted to the magnet unit 40 are repelled, and in FIG. 4F, the holding device can be pulled away from the slope while the article is attracted.

  If the end face 26 on the slope side of the magnet 25 and the front end face 47 of the magnet unit 40 are opposite magnetic poles, the magnet 25 and the article 90 are attracted when the holding device is pulled apart in FIG. May come off.

  The slope base of this embodiment can stop the article at a fixed position by embedding a magnet in the slope. Further, the slope base of the present embodiment can be easily downsized due to its simple structure. If a slope base without a magnet is used, the article is decelerated by lengthening a small slope portion of the slope, and the article stopped at the end of the slope or a stop member will be taken up. However, in the case of a minute and light article, it is often flipped over by a slope or a stop member, and the position to stop is not constant. By using the slope base and the holding device of the present embodiment, the article can be picked up more reliably.

  Next, some modified examples of the holding device will be described.

  A second embodiment of a holding device used for picking up articles will be described with reference to FIGS. The holding device of the present embodiment is different from the first embodiment in the configuration of the magnet unit.

  In FIG. 5, the magnet unit 41 of the holding device 11 includes two members. The front member is a permanent magnet 51. The rear magnetic member 61 may be a permanent magnet or a soft magnetic member made of a soft magnetic material. As the soft magnetic material, various known materials such as iron having high magnetic permeability can be used. Preferably, the foremost member of the magnet unit is a permanent magnet. This is because a stronger adsorption force can be obtained.

  In addition, the structure of a magnet unit is not restricted to the thing of FIG. For example, the magnet unit may be composed of a single permanent magnet as in the first embodiment. For example, as shown in FIG. 6, the magnet unit 43 may arrange | position the soft magnetic member 63 ahead, and may arrange | position the permanent magnet 53 back. More generally, the magnet unit may be configured by one permanent magnet or a combination of a plurality of magnetic members including at least one permanent magnet.

  Returning to FIG. 5, even when the magnet unit is composed of a plurality of magnetic members as in the present embodiment, it is preferable to use a permanent magnet having a strong magnetic force. This is because articles made of more various materials can be adsorbed. The permanent magnet 51 is preferably an Nd—Fe—B magnet (neodymium magnet). Or the magnetic flux density in the front end surface 47 of the magnet unit 41 is preferably 300 mT or more, more preferably 400 mT or more, and particularly preferably 500 mT or more regardless of the type of the permanent magnet. This makes it possible to adsorb articles made of austenitic stainless steel that is not adsorbed by general magnets and articles made of many alloys containing iron, cobalt, nickel, chromium, manganese, and the like as components. Moreover, a micro article | item can be conveyed at high speed by hold | maintaining strongly with a strong magnetic force. From the viewpoint of easy availability, the magnetic flux density of the permanent magnet is preferably 700 mT or less.

  A method of fixing the magnet unit 41 to the tip of the movable rod 37 of the air cylinder is not particularly limited, and a method of bonding using an adhesive, a mechanical method using a screw, or the like can be used.

  A method for joining members constituting the magnet unit 41 is not particularly limited. In FIG. 5, the permanent magnet 51 at the front is attracted and coupled to the magnetic member 61 adjacent at the rear by a magnetic force. In order to employ this structure, it is necessary that the attracting force between the permanent magnet 51 and the magnetic member 61 is significantly larger than the attracting force between the magnet unit 41 and the article. For example, if the permanent magnet 51 is a Ne—Fe—B magnet and the article does not reach a general magnet, the attractive force between the permanent magnet 51 and the magnetic member 61 is remarkably large. it can. With this structure, the permanent magnet 51 can be replaced very easily.

  The size of the permanent magnet 51 is preferably larger in that a strong magnetic force can be obtained. On the other hand, in the holding device of the present embodiment for a minute article, the holding device itself is desirably small, and the outer diameter in a cross section perpendicular to the sleeve axis is preferably 40 mm or less, more preferably. 20 mm or less. In practice, the type and size of the magnet for obtaining the required attractive force will be determined according to the type of article and the content of handling, and the sleeve will be selected according to the outer shape of the magnet. The length of the permanent magnet in the sleeve axial direction is not particularly limited. The longer the magnet, the stronger the magnetic force, so an appropriate length can be selected as necessary.

  In the present embodiment, the permanent magnet 51 is annular. When there is a hole in the attracting surface of the article, this shape acts as a magnetic positioning means for the article when the foremost member of the magnet unit is annular or cylindrical. This will be described below.

  When the article is attracted to the magnet, a force is applied to change the position and orientation of the article so that the lines of magnetic force emitted from the magnet pass through the article as much as possible. Many small parts have holes formed for fixing. The tendency to change the position and orientation at the time of suction becomes particularly remarkable when a hole penetrating the article is formed on the suction surface of the article.

  FIG. 7A shows a plan view of an article 91 in which a hole 97 is formed. When such an article is attracted to a magnet without a hole, for example, a cylindrical magnet 50, the article moves at the moment of adsorption, and the position or orientation is likely to change (change from FIG. 7B to FIG. 7C). . Moreover, even if it adsorbs once, an article | item will move easily during conveyance, and an article | item will also move easily at the moment of releasing an article | item. This phenomenon can also occur when an annular or cylindrical magnet 51 having a hole 57 is used (change from FIG. 7D to FIG. 7E). However, once the magnet hole 57 is concentric with the article hole 97 and the magnet is brought close to the attracting surface and is attracted, the position and orientation of the article are stabilized (FIG. 7F). In the holding device of the present embodiment, the magnet unit 41 can be brought close to and adsorbed while pressing the article with the sleeve so that the hole of the permanent magnet 51 and the hole of the article are concentric. Goods do not move easily. In order to suppress the deviation of the article due to the high-speed conveyance, it is preferable to provide a non-slip portion at the sleeve opening end 31 as described above.

  The operation of picking up an article using the holding device 11 of the present embodiment is basically the same as that of the first embodiment. This embodiment is different from the first embodiment in that the holding device 11 is operated so that the hole 57 of the permanent magnet 51 and the hole 97 of the article 91 are concentric in the picking operation. When the holding device 11 is used, the magnet unit is adsorbed while the sleeve is brought into contact with the article and the article is pressed, so that the article does not move at the moment of adsorption, and the hole of the permanent magnet 51 and the hole of the article are concentric. Thus, the magnet unit can be adsorbed. When the two holes are concentric and the suction is completed, the position of the article is not likely to be shifted or the direction is changed during the conveyance.

  Next, a third embodiment of a holding device used for picking up articles will be described with reference to FIG.

  In FIG. 8, the holding device 15 of this embodiment is different from that of the second embodiment in that the permanent magnet 55 is spherical. Thus, when the center part of the front end surface 47 of the magnet unit 45 is a spherical surface convex forward, physical positioning can be performed when adsorbing an article having a hole. The shape of the permanent magnet 55 is not limited to a spherical shape, and may be a hemispherical shape, for example.

  Also in this embodiment, the first magnetic pole (for example, N pole) is formed on the front end surface 47 of the magnet unit 45. When the spherical permanent magnet 55 is coupled to the magnetic member 65 adjacent to the rear by magnetic force alone, the permanent magnet 55 is oriented so that the first magnetic pole comes to the front end face correctly by using a rod-shaped permanent magnet as the magnetic member. Can be combined. In this case, the magnetic force of the bar magnet may be weak.

  The operation of the holding device 15 of the present embodiment is basically the same as that of the first and second embodiments. This embodiment is different from the first and second embodiments in that the holding device 15 is operated so that the spherical surface of the permanent magnet 55 fits into the hole 97 of the article 90 in the picking operation. When the holding device 15 is used, the article is held in a state where the spherical surface of the permanent magnet 55 is slightly inserted into the hole of the article, so that the position of the article is not shifted during conveyance and the direction is hardly changed.

  The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the technical idea.

  For example, the magnet embedded in the slope may be an electromagnet.

  The slope base of the present invention is not limited to taking out from a pallet, but can be used in various scenes where a minute article is handled. For example, when an article is supplied to a remote place, a slope base may be connected to the end of the conveyance path.

  Moreover, if the slope base of this invention adsorb | sucks to a magnet, it can be used with respect to various articles | goods. Examples of such articles include micro magnets, bolts, nuts, carbide tips, tablets, cam parts, connector pins, and the like.

10, 11, 15 Article holding device 20 Slope base 21 Slope 22 First part of slope 23 Second part of slope 25 Magnet 26 End face on the slope side of magnet 27 End face on the opposite side of the slope of magnet 30 Sleeve 31 Sleeve opening end 32 Sleeve opening 35 Air cylinder (linear actuator)
36 Air cylinder body 37 Air cylinder movable rod 38 Flange 40, 41, 43, 45 Magnet unit 47 Front end surface of magnet unit 48 Rear end surface of magnet unit 50, 51, 53, 55 Permanent magnet 57 Permanent magnet hole 61, 63 , 65 Magnetic member 70 Parallel clamp 90, 91 Article 97 Hole in article

Claims (10)

A slope made of non-magnetic material;
A magnet embedded in the slope,
The magnet has a first magnetic pole at the end face on the slope side.
Slope base for picking up goods. The slope is
A first portion whose slope decreases toward the bottom;
Having a second portion that is smoothly continuous from the lower end of the first portion and has a constant slope;
The magnet is embedded in the second portion;
The slope base for article collection according to claim 1. The magnet is a Nd-Fe-B magnet;
The slope base for article collection according to claim 1 or 2. The magnetic flux density on the surface of the slope by the magnet is 300 mT or more.
The slope base for article collection as described in any one of Claims 1-3. A method for picking up an article using the slope table according to any one of claims 1 to 4,
Dropping an article on top of the slope;
Attracting the magnet to slide down the slope and causing the magnet to stand still;
A magnet unit that is configured by one permanent magnet or a combination of a plurality of magnetic members including at least one permanent magnet, and in which the first magnetic pole is formed on the front end surface, uses a holding device that can linearly move in the sleeve. Abutting the sleeve against the stationary article with the magnet unit retracted;
Advancing the magnet unit to attract the article to the holding device;
Pulling the entire holding device away from the slope;
A method for picking up an article. The holding device has an annular or cylindrical shape in which a frontmost member among the members constituting the magnet unit has a hole penetrating in the axial direction of the sleeve.
The method for picking up articles according to claim 5. In the holding device, at least a central portion of the front end surface of the magnet unit is a spherical surface convex forward,
The method for picking up articles according to claim 5. The holding device has a permanent magnet as a frontmost member among members constituting the magnet unit.
The article pickup method according to any one of claims 5 to 7. In the holding device, the permanent magnet is an Nd-Fe-B magnet.
A pair of article picking method as described in any one of Claims 5-8. The holding device has a magnetic flux density of 300 mT or more at a front end surface of the magnet unit.
A pair of article picking method as described in any one of Claims 5-9.

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