United States Patent 3811667

A holding or clamping device of the type comprising two pressure cylinders adapted to produce a first preliminary weak holding force and subsequently a greater holding force is provided with a sensor pin adapted to bring about a switch over from operation of the first cylinder to the second cylinder. The sensor pin is so loaded that it will only bring about the switching over when it strikes a hard object such as metal but is not actuated when it comes into contact with the human hand.

Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
91/209, 91/401, 91/519
International Classes:
B23Q3/06; B23Q3/08; F15B15/20; (IPC1-7): B25B1/18; F01B15/02
Field of Search:
91/206-209,401,411A 100
View Patent Images:
US Patent References:
2805447Safety circuit for molding machine1957-09-10Voges
2693752Repeat action press1954-11-09Garapolo

Primary Examiner:
Lake, Roy
Assistant Examiner:
Abrams, Neil
Attorney, Agent or Firm:
Ostrolenk, Faber, Gerb & Soffen
1. A pneumatic holding device for workpieces, comprising:

2. The structure as set forth in claim 1, comprising an inlet check valve connecting said pressure space of the second cylinder with the atmosphere.

3. The structure as set forth in claim 2, comprising an adjustable choke

4. The structure of claim 1, further comprising a low pressure piston communicating with said first cylinder to be moved by the pressure in that

5. The structure of claim 4, wherein said abutment sensor comprises a slidable pin projecting beyond said jaw operative surface and slidable back through said jaw upon application of pressure thereto; said pin being

6. The structure of claim 5, wherein said valve includes a sealing plate in said first cylinder that is positioned to be subject to the pressure in said first cylinder and that is movable by the pressure in said first cylinder to a position which closes said conduit and that is of a size to

7. The structure of claim 6, further comprising a plunger carried on said sealing plate for moving same; said plunger extending toward said slidable pin; said slidable pin extending to a position to engage said plunger when pressure is applied to said slidable pin, thereby causing said slidable pin to press upon said plunger, and said plunger and said sealing plate being positioned such that said sealing plate is moved to open said conduit upon pressure being applied upon said slidable pin in the

8. The structure of claim 7, further comprising:

9. The structure of claim 8, wherein said low pressure piston comprises a piston rod to which said jaw is connected and on which said jaw is supported; said piston rod is hollow and within that hollow defines said first cylinder; said first and second cylinders are coaxial;

10. The structure of claim 9, wherein said conduit further comprises an annular chamber surrounding said piston rod, and a radial connection through said valve housing between said annular chamber and said first

11. The structure of claim 8, wherein said valve plunger has a rest position at which said sealing plate is against said valve housing; said slidable pin having a rest position projecting above said jaw; in their respective rest positions, said slidable pin and said plunger being gap spaced, and said slidable pin being so placed and shaped that when it is depressed toward said jaw, it contacts and then moves said plunger, thereby moving said sealing plate off said valve housing and opening said

12. The structure of claim 5, wherein said first and low pressure pistons

13. The structure as set forth in claim 12, in which said valve housing carries the jaw in a rocking manner and the sensor pin extends through a

14. The structure as set forth in claim 11, comprising a sliding piston connected to said sensor pin for moving said sensor pin in a hole in the valve housing, and a spring which biases said sensor pin out of said jaw

15. The structure as set forth in claim 1, in which said first cylinder

16. The structure as set forth in claim 1, comprising a return spring

17. The structure of claim 12, wherein said first and second cylinders are

18. The structure of claim 12, wherein said low pressure piston comprises a piston rod to which said jaw is connected and on which said jaw is

19. The structure of claim 18, wherein said first and second cylinders are

20. The structure of claim 18, wherein said first and second cylinders are coaxial; said first piston surrounding and being coaxial with said piston

21. The structure of claim 20, wherein said piston rod is hollow and defines within itself said first cylinder.


1. Field to Which Invention Relates

The invention relates to a pneumatic holding device for clamping workpieces with two holding cylinders having different diameters, of which the first, with the smaller diameter, brings about a preliminary movement with a small thrust or force while the second, the main cylinder with a larger diameter, provides the holding force at the end of the preliminary movement.

2. The Prior Art

Such safety holding cylinders have the aim of preventing accidents, such as crushing of the hand, which may result owing to the high impact force of commercially conventional pneumatically operated cylinders if the operator should depart from operating instructions and place his hands between the parts to be pressed together. In the case of holding cylinders of a conventional construction cases are continually arising of operators suffering injuries to their hands or fingers owing to unintentional operation when owing to lack of alertness the operator places his hand between the workpiece and the pressing plate of the holding cylinder.

Therefore, for reasons of safety there is the aim of causing the preliminary movement to take place with a considerable reduction in thrust or pressing force and only producing the full force when the jaw or pressing plate and the workpiece have come into contact.

In the case of a previously proposed holding device of the above-mentioned construction two superposed cylinders with different diameters are provided which come into action one after the other. The switching over from the small pressing force to the very much greater holding force is carried out by means of a control system arranged outside the cylinders and this makes it necessary to have two air ducts leading to the holding element, the one duct providing the cylinder with the small diameter and the second duct providing the cylinder with the larger diameter with compressed air respectively.


One aim of the invention is to simplify this control device and to ensure that the switching over only occurs when the holding cylinder jaw or pressing plate engages the workpiece but does not do so if contact should be made with the finger or hand placed inbetween.

In order to attain this and other objects there is the provision of an abutment sensor which opens a valve in order to place the main cylinder under pressure. Preferably this valve is provided between the first cylinder and the main holding cylinder. The abutment sensor can be constructed as a pin which is guided in a hole in the jaw of the holding cylinder so that the valve can only be actuated when the sensor pin comes to engage a hard obstacle such as wood or metal. The valve, which switches over from the cylinder with a low thrust to the full holding force can, however, not be operated by a soft obstacle such as a hand. The invention thus ensures with certainty that the presence of the finger or hand cannot lead to the application of the dangerously high holding or clamping force which could lead to injury by crushing. Since all parts, which are necessary for the function of the cylinder, are arranged in the cylinder itself, the latter can be connected directly with a compressed airline just as is the case with any conventional holding or clamping cylinder.

The thrust or pressing force supplied by the first preliminary advancing cylinder is so small that the piston rod can be stopped by hand. It is thus always possible to withdraw the hand from between the workpiece and the pressing plate or jaw without any injury being incured.

In many cases it will be convenient to so fix the holding cylinder, in order to ensure ease of insertion of the workpieces, that in the rest position of the cylinder there is a large space left between the workpiece and the jaw or platen. This type of operation in accordance with the invention ensures that there is no danger whatsoever for the operator.

The pneumatic holding device cannot only be used for holding workpieces but also for other purposes, for example for frame presses and similar holding devices in the case of which there also was a danger of injury.


In what follows an embodiment of the invention will be described with reference to the drawing. The single FIGURE of the drawing shows a side view of a pneumatic holding or clamping device in accordance with the invention.

The holding or clamping device comprises a front housing part 10, which serves for fixing the position of the whole holding device on a holding rod 12. The fixation of the stationary part of the housing can be carried out in a different manner. This front housing part comprises a double-walled cylinder with an outer wall 14 and an inner wall 16. The wall 16 forms the first or preliminary advancing cylinder and simultaneously the piston rod of the main holding piston 18 carried by it. This main holding piston 18 slides in the main holding cylinder 20, which is mounted in the front housing part 10. The main holding cylinder 20 is provided with a cylinder end closure 22, which is connected in a fixed manner with the plunger piston 24 of the first preliminary advancing cylinder 14, 16. The main holding piston 18 is acted upon by a return spring 26 on the front housing part 10. The front cylinder end closure of the preliminary advancing cylinder is formed by a valve body 28, which has a central opening, which guides a valve plunger 30 with a sealing plate 32. The valve plunger 30 is provided with axial ducts 34, which are connected via radial holes 36 of the valve body 28 with the annular duct 38 between the two cylinders 14 and 16. This annular duct 38 is connected via holes 40 with the pressure chamber 42 of the main pressure or holding cylinder. This space 42 is connected via a check valve 44 and an adjustable choke 46 with the external air.

On the front part of the valve body 28 there is a jaw or platen 48 which is mounted in a pivoting or swinging manner. In a hole 50 in this jaw 48 there lies a sensor pin 52, which with a sliding piston or plunger 54 slides in an inner hole of the valve body. The sensor pin 52 is biased in an outward direction by a helical compression spring 56. The valve 30, 32 is biased or urged onto its seat by means of a helical compression spring 58.

The manner of operation of the device is as follows:

The pressure medium is supplied to the preliminary advancing cylinder via an axial hole 60 in the plunger piston 24. As a result pressure is built up in the cylinder space 62 so as to advance the cylinder 14, 16 and the holding piston 18. In order to avoid the formation of a vacuum in the pressure space 42 of the holding cylinder the check valve 44 and the metering valve 46 are provided. With the metering valve 46 the amount of air supplied can be regulated and in this manner the advancing speed of the piston 18 can be adjusted at will. Owing to the pressure built up the sealing plate 32 of the valve plunger 30 is pressed correspondingly firmly against its seat. If now the sensor pin 52, which extends for about 1 mm proud from the platen or jaw 48, now runs up against a solid body such as wood or metal, the sealing plate 32 will be raised and the pressure can now pass through the holes 36 of the valve body and the annular duct 38 and the hole 40 towards the pressure space 42 of the main holding cylinder. As a result the main holding piston 18 exerts its full holding or clamping force. If the air supply is turned off and the device is vented, the spring 26 presses the piston back again. Venting occurs in this case in the opposite direction and the valve plunger 30, which can easily be displaced, is raised by the returning air.

The valve placed between the preliminary advancing cylinder and the main cylinder operates as follows.

(Force measurements are in terms of kilograms (kg.) wherein 1 kg = 9.80665 Newton.)

In the case of, for instance, an operating pressure of 8 kg per square centimeter and a diameter of the plunger piston 24 of 18 mm an advancing force of 20.35 kg is produced. If one allows for a reduction of about 4 kg in the advancing force owing to the frictional resistance of the piston 18 and owing to the counter-pressure of the spring 26, there will in fact be an advancing force of approximately 16 kg. The sealing plate 32 of the valve plunger 30 has a diameter of 15 mm and is thus forced with a force of 8 kg per square centimeter against its valve seat. Therefore, a counter-pressure of 14.24 kg is necessary in order to raise the valve plate. The sensor pin at the jaw has a diameter of 8 mm so that a comparatively hard article of wood, metal or the like is necessary in order to raise the valve plunger 30. In the case of a soft obstacle the pressing force distributes itself, as supposed above, on the jaw, which has a diameter of at least 50 mm. The pressing force is 16 kg. There is thus no possibility of such a strong counter-pressure being produced at the end of the sliding piston 54 that the valve plunger 30 is raised. The two-part valve insert 30 and 54 is necessary because for a secure closure of the valve and also for venting of the valve plunger 30 great freedom of movement is necessary. For this reason the seal at the outer periphery of the sliding piston 54 is provided, which is pressed by a compression spring 56 outwards against an abutment ring 64. Between the sliding piston 54 and the valve plunger 30 there is an intermediate space of for example 0.3 mm. The above data more particularly as regards dimensions and pressures are not binding and only serve as an example. The cylinder can -- in accordance with the particular requirements to be met -- be constructed with other dimensions.