Regulator for a compressed-air-driven vacuum generator, the regulator arranged to maintain a negative pressure in a gripper actuated by vacuum.

TECHNICAL FIELD OF THE INVENTION The present invention relates to a regulator that is effective to maintain a negative pressure in a tool or gripper that is activated by vacuum and supplied by a compressed-air-driven vacuum generator.

BACKGROUND AND PRIOR ART

Compressed-air-driven vacuum generators are notoriously known per se and do not need any explanation in more detail. Neither is the regulator of the invention limited to a certain type of vacuum generator and is applicable together with an arbitrary vacuum generator that is adapted to be fed with compressed air in order to produce a negative pressure or vacuum to the level that is required to activate a tool or gripper, such as a suction cup. The regulator may advantageously be utilized together with one or more ejectors or ejector vacuum pumps that individually may be formed with one or more vacuum steps arranged in series.

Negative pressure or vacuum has versatile use within the industry for holding, lifting and moving objects of varying kinds, such as materials, manufacturing parts, products, and packages. In this connection, it should be observed that here, the expression vacuum is used to denote a negative pressure that is useful for an industrial process and has not to be regarded as an absolutely pressureless state. For gripping an object, typically a suction cup is utilized that by surrounding atmospheric pressure is pressed into sealing contact and attachment against the surface of the object when the pressure inside the suction cup is lowered by means of the vacuum generator.

Upon the handling of hard objects having a smooth surface, usually a grip is maintained between the suction cup and the object until the negative pressure inside the suction cup actively is broken by the inlet of atmospheric pressure or by the feeding of compressed air into the suction cup. In these cases, the feeding of compressed air to the vacuum generator may cease entirely when the requisite vacuum level to attach the suction cup onto the object has been reached.

Upon the handling of hard objects having a rough or porous surface, as well as upon the handling of soft objects and objects having an irregular or compliant surface, it is often a problem to achieve sealing between the suction cup and the object, and therefore leakage of ambient air into the suction cup may arise. In these cases, a compensating feeding of compressed air to the vacuum generator is required to maintain a vacuum level that guarantees the engagement of the suction cup with the object. A conventional way to solve this problem is to continuously feed compressed air into the vacuum generator at a quantity that by a margin guarantees that a satisfying grip between the suction cup and the object always is provided. It will be appreciated that, in that connection, at least periodically, more compressed air and energy than what is necessary will be consumed. SUMMARY OF THE INVENTION

The object of the invention is to provide an energy-saving solution of the problems mentioned above.

The object is met by a regulator, adapted to, in co-operation with a compressed-air- driven vacuum generator, maintain a negative pressure in a gripper activated by vacuum, which regulator comprises a process-air duct for the supply of compressed air to the vacuum generator and a flow-regulating slide that is movably arranged in the process-air duct and biased to move toward a flow-reducing position, as well as a control means actuating the slide and the force of which against the slide in the opposite direction of motion is determined by the pressure prevailing at each instant of time on the vacuum side of the vacuum generator, which via a control duct is led into the control means in the regulator. The slide is movably mounted in a lining standing transverse to the process-air duct and having mutually opposite openings in the wall of the lining for process-air flow through the lining and the slide. The technical effect of this solution is an immediate and proportional adaptation of the compressed-air consumption to any change of the negative pressure on the vacuum side of the vacuum generator, to which the gripper is connected.

The openings may be made as slots that extend in the circumferential direction of the lining, an area around the openings being countersunk in the envelope surface of the lining so as to allow distribution of compressed air to the end areas of the slots.

The control means is suitably made as a push rod that is movably mounted in the regulator and loads the slide by the total force from a biasing spring and the pressure prevailing in the control duct. The technical effect of this preferred embodiment is that the sensitivity and reaction of the regulator on changes of the pressure in the control duct can be determined by a suitable dimensioning of the force of the spring of the control means so as to allow a continuous optimization of the compressed-air consumption. In other words, the biasing force of the spring that actuates the push rod is dimensioned to, at normal atmospheric pressure in the control duct, adjust the slide into an open position for unimpeded flow of compressed air through the process-air duct. On the other hand, the biasing force of the spring is dimensioned to, at negative pressure in the control duct, allow the slide to move to a flow- reducing position in which the flow through the process-air duct is limited.

In an advantageous embodiment, the force of the spring is adjustable for changing the sensitivity of the regulator and/ or for determining a threshold vacuum level and adapting the power of the vacuum generator to different types of objects and applications. In this embodiment, the regulator can provide a threshold vacuum level to which the vacuum generator is driven at full power, before the process-air flow to the vacuum generator is reduced as a result of the total force from the biasing spring of the control means and the pressure in the control duct being counterbalanced by the bias of the slide toward a flow-reducing position in the process-air duct. In other words, by dimensioning and/ or by adjustment of the biasing force of the spring, the regulator can be adapted to not allow the slide to move to a flow- reducing position in which compressed-air flow through the process-air duct is limited before a determined negative pressure in the control duct is reached.

In a preferred embodiment of the regulator, the push rod is actuated by a flexible diaphragm that is mounted in the regulator and loaded by the biasing spring and by the pressure in the control duct. By the diaphragm, a comparatively large surface and high sensitivity to variations of the pressure prevailing in the control duct are provided.

In a conceivable alternative embodiment of the regulator, the push rod is actuated by a piston that is movably mounted in the regulator and loaded by the biasing spring and by the pressure in the control duct.

The push rod actuates in turn the flow-regulating slide that is movably mounted in the lining standing transverse to the process-air duct. Suitably, the lining has the shape of a cylinder, the slide being made as a circular- cylindrical piston that is displaceably received in the lining and has a section with reduced radius situated between two piston sections with full radius. Mutually opposite openings in the wall of the lining allow flow of compressed air through the lining and the slide.

In an alternative embodiment, the slide consists of a piston having two or several sections with reduced radius that are axially separated by sections with full radius, while the lining has correspondingly situated openings on axially different levels in the longitudinal direction of the lining. An advantage of this alternative embodiment is that the stroke of the slide between closed and fully open position is reduced correspondingly, and therefore also the dimensions of the regulator can be reduced.

The slide has a seat for the accommodation of a spring that biases the slide in the direction of a flow-reducing position in which a piston section with full radius at least partly covers the openings in the wall of the lining and correspondingly limits the flow of compressed air through the process-air duct.

Further details and embodiments of the invention are seen below in the detailed description and in attached claims. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail below with a reference to the appended drawings that schematically illustrate preferred embodiment examples of a regulator according to the invention. In the drawings

Fig. 1 shows a longitudinal cross-section through the regulator, and Fig. 2 shows a broken-away longitudinal cross-section of an adjustment device included in the regulator.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT EXAMPLE

The regulator 1 is arranged in a housing 2 having a traversing process-air duct 3 that in a first or upstream end 4 is connectable to a source of compressed air, in Fig. 1 only schematically indicated and designated P. The second or downstream end 5 of the process-air duct 3 is connectable to one or more vacuum generators coupled after, such as one or more ejector vacuum pumps, which in Fig. 1 are represented schematically by an ejector designated 6. The flow directions of the compressed air and evacuated air in the vacuum generator and the regulator are seen from arrows in Fig. 1.

Transverse to the process-air duct 3, there is formed a seat 7 in the housing 2 for the fitting of a lining 8 with a slide 9 movably received in the lining. The seat 7 has a circular cross-section and the lining 8 has the shape of a cylinder insertable into the seat. The seat 7 and the process-air duct 3 have intersecting centre axes, however both the seat and the lining have a radius that exceeds the radius of the process-air duct so that the mouths of the process-air duct cover a limited part of the envelope surface of the lining on opposite sides of the lining. Right in front of the mouths of the process-air duct, a respective opening 10 and 1 1 is recessed through the wall of the lining. The openings 10 and 1 1 may be dimensioned to correspond to the area and the shape of the respective mouth of the process-air duct. A more compact design with a lower height as seen in the longitudinal direction of the lining may, however, be achieved if the openings, as in the embodiment example, are made as slots having a smaller height than the mouths of the process-air duct, but which, on the other hand, extend past the mouths in the circumferential direction of the lining, an area 12 around the openings 10, 1 1 being countersunk in the envelope surface of the lining for distributing compressed air to the end areas of the slots. The opening angle as measured from the centre of the lining may, in that connection, amount to the order of 120° between the ends of the openings/ slots.

The slide 9 is in the form of a circular- cylindrical piston having a section 13 with reduced radius situated between two piston sections 14 and 15, respectively, with full radius, and more precisely with a full radius that allows the slide 9 to be inserted into the lining 7 in order to be unimpededly displaceable in the

longitudinal direction of the lining. A spring 16 acting between the slide 9 and the bottom of the seat biases the slide toward the top of the seat and toward a flow- reducing position in which the section 15 of the piston with full radius at least partly covers the openings 10 and 1 1 and in that connection limits the flow area and reduces the flow of compressed air through the lining and the slide.

In an alternative embodiment (not shown in the drawings), the slide consists of a piston having two or more sections with reduced radius that are axially separated by sections with full radius, while the lining has correspondingly situated openings on axially different levels in the longitudinal direction of the lining. In Fig. 1, the slide 9 is however shown in an open position in which compressed air for the driving of the ejector 6 can flow unlimitedly through the process-air duct 3, the openings 10, 1 1 of the lining, and past the reduced piston section 13 of the slide 9. The adjustment of the slide between the shown open position and a flow- reducing position is controlled by the control means described below that is accommodated in the housing 2, preferably in a separate part 2' of an assembled housing 2. More precisely, the control means comprises a push rod 17 that actuates the slide 9 from above and that, from a hollow space axially aligned with the seat 7, extends through the bottom of the hollow space into the seat, into abutment against the top of the slide 9. In its upper end, the push rod 17 is anchored in the under side of a flexible diaphragm 18, the periphery of which is anchored in the wall of the hollow space and divides the hollow space into an upper chamber 19 and a lower chamber 20.

In the upper chamber, and in the direction of the upper side of the diaphragm 18, a control duct 21 mouths that, on the outside of the housing 2, is connectable to the vacuum side of the vacuum generator, in Fig. 1 represented by a cavity 22 surrounding the ejector 6 and from which air is evacuated when driving the ejector so as to allow activation of a tool or gripper 23 connected to the cavity 22. In the lower chamber and in the direction of the under side of the diaphragm, a ventilating duct 24 mouths that is open or can be opened to surrounding atmosphere. The control duct 21 comprises a control duct section 2 Γ axially aligned with the chambers 19, 20 and the seat 7 and in which there is accommodated a biasing spring 25 that acts in the direction of the upper side of the diaphragm. By dimensioning the force of the spring 25, the sensitivity and reaction of the regulator on changes of the pressure in the control duct can be determined so as to allow a continuous optimization of the compressed-air consumption. No detailed provision for the dimensioning of the spring 25 is given here, because this should be tried out for each application. However, it is realized that the spring 25 should have strength to, at least when there is atmospheric pressure in the control duct 21 , 21', balance the force of the spring 16 that biases the slide 9 toward a flow- reducing position. In the embodiment example shown in Fig. 2, the spring 25 is assigned an

adjustment device 26 arranged on the outside of the housing in the form of a rotatable cap that, by means of a set screw 27, can be fixed in the adjusted rotational position on a stud 28 projecting from the housing 2. The cap 27 is in engagement with an axially movable but rotationally fixed screw 29 that projects into the control duct section 2 into engagement with the spring 25. The

adjustment device is effective for the adjustment of the load of the spring on the diaphragm 18, and provides in this way, where appropriate, also

adjustment/ change of a threshold vacuum level up to which the slide 9 remains immovable in the lining 7 in order to, in its open bottom position, allow unlimited flow of compressed air through the process-air duct 3. Finally, it should be mentioned that the regulator 1 alternatively may be integrated in a vacuum generator or be arranged to be assembled with a vacuum generator housing, as well as it can be arranged separately from the vacuum generator/ the vacuum generator housing and communicate with the vacuum generator via lines for compressed air and vacuum. It also deserves to be mentioned that the regulator can be assigned replaceable linings with openings /slots of different size, for instance with the purpose of adapting the process-air flow to the capacity and air requirement of a vacuum generator coupled after. Furthermore, it should be emphasized that any reference above to spatial relations only relates to the orientation of the regulator in the drawing figures and is not intended to describe its position in use, which is not limited to the shown orientation.