Rodless Cylinder

(1) Field of the Invention

This invention concerns a rodless cylinder.

(2) Description of the Prior Art

Cylinder apparatus in which a piston driven within a cylinder tube by the pressure of a fluid introduced therein have often been utilized generally. In the cylinder apparatus of this type, a rod mounted to the piston is extended from one end of a cylinder tube externally and a load is connected to the top end of the rod. However, in a state where the rod is projected to its extreme stroke end out of the cylinder tube, the entire length including the rod and the cylinder tube is approximately twice as long as the rod stroke. Thus, the cylinder apparatus of this type requires a relatively large installation space as compared with the stroke of the piston rod.

In view of the above, a so-called rodless cylinder has been developed as disclosed in Japanese Patent Publication No. 25034/1980 filed in Japan based on British Patent Application No. 4890/1971, in which a piston and an operation member slidion along the outer circumferential surface of a cylinder tube are mounted with permanent magnets respectively and the operation member is moved along the cylinder tube by utilizing the attraction force between the permanent magnets. FIG. 1 shows a schematic structure of the rodless cylinder, wherein a piston 2 disposed in a cylinder tube 1 and an operation member 3 fitted over the outer circumferential surface of the cylinder tube 1 are respectively mounted with magnet rows each consisting of a plurality of permanent magnets 4, 4, . . . and 5, 5, . . . arranged side by side and the different poles of the individual magnets in each of the magnet rows are opposed to each other respectively, so that the operation member is moved by the attraction force between the permanent magnets 4 and 5 following after the movement of the piston 2 driven by the pressure of a fluid. By the way, in the rodless cylinder as described above, the magnets 4 and 5 are arranged in the axial direction of the cylinder tube 1 with the different poles of the individual magnets in each of the magnet rows being adjacent to each other. Accordingly, it is necessary to increase the magnetic force, i.e., the size, or the number of the magnets constituting the magnet row in order to enhance the attraction of holding force between the magnet rows. This, however, increases the size and the cost of the entire apparatus, which is contrary to the essential purpose of the rodless cylinder of reducing the apparatus size.

Accordingly, it is an object of this invention to provide a rodless cylinder capable of obtaining a greater attraction force between a driving magnet row mounted to a piston and a driven magnet row disposed to the outer circumferential surface of a cylinder tube with no changes in the size and the number of the magnets by providing an adequate pole arrangement for the individual magnets in each of the driving and driven magnet rows.

Another object of this invention is to provide a rodless cylinder capable of obtaining a greater attraction force between the driving magnet row and the driven magnet row, which enables the use of small-sized magnets, thereby reducing the size and the cost of the apparatus.

A further object of this invention is to provide a rodless cylinder in which the driven magnet row can surely move following after the movement of the driving magnet row by a greater attraction force between the driving magnet row and the driven magnet row.

Other objects and aspects of this invention will become clearer by reading the following explanations for preferred embodiments of this invention in conjunction with the appended drawings.

The above objects can be attained by the rodless cylinder in accordance with this invention, in which a driving member driven within a cylinder in a axial direction by the pressure of a fluid is constituted by mounting a driving magnet row to a piston sliding in the cylinder and a driven member disposed to the outer circumference of the cylinder axially slidably is mounted with a driven magnet row, wherein a plurality of individual magnets disposed axially to the cylinder in each of the magnet rows are arranged such that the identical poles of the individual magnets are in adjacent to each other, and each of the magnet rows are arranged such that the different poles of the individual magnets are opposed to each other.

FIG. 1 is a cross sectional view for a part of a conventional rodless cylinder,

FIG. 2 is a side view for a preferred embodiment according to this invention,

FIG. 3 is a cross sectional view taken along the line A--A in FIG. 4, and

FIG. 4 is an end view of the rodless cylinder shown in FIG. 2.

This invention is to be described specifically by way of its preferred embodiment referring to the drawings. In FIG. 2 through FIG. 4 are shown a cylinder 11, a pistonlike driving member 12 inserted fittedly to the inside of the cylinder 11 axially slidably and a driven member 13 which moves following after the movement of the driving member 12.

The cylinder 11 comprises a cylinder tube 14 made of non-magnetic material such as aluminum and head covers 15, 15 threadingly secured to the both ends thereof. Each head cover 15 is perforated with charge and discharge ports 17a, 17b for high pressure fluid in communication with the inside of the cylinder tube 14 by way of through holes 16.

The driving member 12 is adapted to reciprocate axially within the cylinder by the pressure of a high pressure fluid charged and discharged to and from the charge and discharge ports 17a, 17b in the head covers 15, 15. The driving member 12 comprises a driving magnet row 20 formed by alternately arranging a plurality of permanent magnets 18, 18, . . . and yokes 19, 19, . . . each with a central aperture, which are put between a pair of pistons 21, 21 and integrated, by being clamped with a bolt 22 inserted through the central apertures and a nut 23, together with dampers 24, 24 for abutting against stoppers 15a situated on the stroke ends within the cylinder, damper washers 25, 25 for restricting the compression of the dampers and flat washers 26, 26 abutting against the surface of the dampers for holding the same.

The driven member 13 in the form of a ring is inserted over the outer circumference of the cylinder tube 14 axially slidably and it comprises a driven magnet row 29 formed by alternately disposed a plurality of ring-like permanent magnets 27, 27, . . . and yokes 28, 28, . . . which are covered by a tube 30 at the outer circumference of the magnet row and fitted with a pair of fixing covers 31, 31 at the both ends of the tube 30 and integrated by being clamped with a bolts 32 inserted between the fixing covers 31, 31.

In each of the magnet rows 20 and 29, individual permanent magnets 18, 27 are arranged axially to the cylinder 11 such that the identical poles of the individual magnets are in adjacent to each other. The magnet rows 20 and 29 are arranged such that the different poles of the corresponding magnets 18 and 27 in each of the rows are opposed radially to each other by way of the cylinder tube 14.

Specifically, in the driving magnet row 20, a plurality of individual permanent magnets 18, 18 are arranged in the adverse direction alternately so that their identical poles S, S and N, N are adjacent to each other. In the driven magnet row 29, a plurality of individual magnets 27, 27, . . . corresponding in the number to that in the driving magnet row are arranged such that their identical poles S, S and N, N are adjacent to each other. Further, the driving magnet row 20 and the driven magnet row 29 are arranged such that the N poles of the individual magnets in the driving magnet row 20 are opposed to the S poles of the individual magnets in the driven magnet row 29 and S poles of the individual magnets in the driving magnet row 20 are opposed to the N poles of the individual magnets in the driven magnet row 29 respectively.

In the drawing, also shown are a pressurized fluid source 33, and a switching valve 34 that switchingly supplies a pressurized fluid from the pressurized fluid source 33 to either one of the charge and discharge ports 17a, 17b in the head cover 15 and discharges the pressurized fluid from the other of the charge and discharge ports to the outside.

In the rodless cylinder having a constitution as described above, when a high pressure fluid is supplied from the charge and discharge port 17a to the cylinder 11 at the switching position shown in FIG. 3, the driving member 12 moves in the direction of the arrow A while discharging the fluid on the opposite side in the inside of the cylinder 11 through the other charge and discharge port 17b, whereby the driven member 13 moves by the attraction force between both of the magnet rows 20 and 29 following after the movement of the driving member 12. Alternately, when a high pressure fluid is supplied to the charge and discharge port 17b, the driving member 12 and the driven member 13 can be driven in the opposite direction.

In the rodless cylinder of the illustrated embodiment, since the magnets 18, 27 in the magnet rows 20, 29 are arranged respectively so that the identical pole of the individual magnets are adjacent to each other in each of the rows, the attraction force between both of the magnet rows 20 and 29 can be made remarkably greater as compared with that of the embodiment shown in FIG. 1, wherein the different poles for the magnets 4, 4, . . . and 5, 5, . . . are adjacent to each other in the axial direction in each of the magnet rows at the inside and the outside of the cylinder 1.

Table 1 shows the results of the measurement for the difference in the attraction force between the magnet rows in each of three types of rodless cylinders having the same basic structure, with respect to the case where the magnets are arranged according to this invention and in the case where the magnets are arranged in the conventional manner as shown in FIG. 1. As apparent from the Table 1, the magnet arrangement according to this invention can increase the attraction force between the magnet rows approximately five times as large as that of the embodiment shown in FIG. 1.

As stated above, the attraction force between the magnet rows can be increased significantly by the rodless cylinder according to this invention, in a simple structure wherein a plurality of individual magnets are arranged appropriately, in each of the driving magnet row mounted to the piston disposed to the inside of the cylinder and the driven magnet row disposed to the outside of the cylinder.