WO2011159173A2

WO2011159173A2 - Non contact lifting device and control system

Info

Publication number: WO2011159173A2
Application number: PCT/NZ2011/000112
Authority: WO
Inventors: Matthew Francis Journee; James Grant Robertson
Original assignee: Powerhouse Ventures Limited
Priority date: 2010-06-16
Filing date: 2011-06-16
Publication date: 2011-12-22
Also published as: WO2011159173A3

Abstract

A non contact lifting device comprising a body including a flat lower surface radially outward of a first angled impingement surface and a plenum with an outwardly facing annular outlet including a nozzle throat. At least one fluid inlet port communicates gases to the plenum. A central lower surface sits below the plenum. The nozzle throat geometry and fluid pressure supplied in use through the fluid inlet port cause a supersonic gases jet to exit the nozzle throat in a radially outwards direction into an area below the first angled impingement surface. The geometry of the first angled surface in a region between the nozzle throat and intersection of the first angled surface and the flat lower surface of the body, maximizes the entrainment effect of gases under the central lower surface by carrying the gases downstream in a radially outwards direction and setting up a toroidal vortex in the area under the first angled surface.

Description

"NON CONTACT LIFTING DEVICE AND CONTROL SYSTEM"

FIELD

This invention relates to the field of non-contact handling devices. More particularly this invention relates to non-contact devices utilizing positive pressure fluid flow to create low pressure zones between the device and a surface so as to attract the surface and device to one another whilst preventing actual physical contact.

BACKGROUND

Non contact lifting devices are known for materials handling applications, where it is beneficial that the lifting device does not come into direct contact with the article being handled. Applications for transporting semi-conductor wafers, glass handling and food handling are known in the art.

Bosch Rexroth manufacture such devices under the NCT series brand of Non-Contact Transfer Units.

The devices are based on the Bernoulli principle.

US20100052345 (Chang et al) discloses a lifting device for semi-conductor wafer transport with two distinct components, whereby a Bernoulli effect is employed in a first fluid port to create a negative pressure zone and a second fluid port is positioned outside the Bernoulli zone to create positive air pressure to repel the article so as to avoid article edge contact with the device.

A drawback of this approach is the need for two separate fluid distribution members to be contained within the device.

Vortex lifters are also known in the art. US7,690,869 (Seikai et al) discloses a non-contact lifting device based on vortex principles whereby a swirl chamber is housed within the device to cause the airflow exiting the device to exit in a rotating motion in order to generate a negative pressure zone between the device and the surface of a workpiece.

A drawback of this approach is the degree of complexity of construction required.

WO2010041965 (Chen) discloses an improved non-contact lifting device which augments the Bernoulli principle with other fluid dynamic forces through pin and pad undercut design thereby entraining adjacent fluids to increase the negative pressure zone and resulting lifting force potential.

(Chen) identifies that high lifting forces are required to enable utilization of non-contact lifters for robotic locomotion applications, such as wall climbing robots. A lift/ flow ratio of around 3.5 (xlO-2) was reported from an adhesion of around 6N from a fluid flow of 50 litres per minute and an absolute inlet fluid pressure of 5 bar.

In the design of non-contact lifting devices there is a trade-off between absolute inlet pressure (bar), volume of airflow (litres per minute) and resulting lifting force (newtons) which impacts the efficiency of lifting devices and which can be represented as a lift/ flow ratio for a given fluid inlet pressure.

Accordingly there is a need for a simple device and method with a significantly increased lift/ flow ratio for applications such as, but not limited to, pick and place and mobile robotics.

SUMMARY OF THE INVENTION

A general object of the present invention is to provide a simple non-contact lifting device and method with improved efficiencies or to at least provide the public with a useful choice.

Other objects of the invention may become apparent from the following description which is given by way of example only.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date.

In one aspect, the present invention may broadly be said to consist in a non contact lifting device comprising a body including a flat lower surface radially outward of a first angled impingement surface, a plenum with an outwardly facing anular outlet including a nozzle throat at least one fluid inlet port communicating gases to the plenum; and a central lower surface below the plenum, wherein the nozzle throat geometry and fluid pressure supplied in use through the fluid inlet port cause a supersonic gases jet to exit the nozzle throat in a radially outwards direction into an area below the first angled impingement surface; and wherein the geometry of the first angled surface in a region between the nozzle throat and intersection of the first angled surface and the flat lower surface of the body, maximizes the entrainment effect of gases under the central lower surface by carrying the gases downstream in a radially outwards direction and setting up a toroidal vortex in the area under the first angled surface.

According to a further aspect, the length of the first angled surface between the nozzle throat and the intersection of the first angled surface and the flat lower surface of the body is a function of the length of the supersonic jet, such that the jet becomes subsonic at or close to, but not beyond, the intersection of the first angled surface and the flat lower surface of the body. According to a further aspect, the first angled surface between the nozzle throat and the intersection of the first angled surface and the flat lower surface of the body is a concave curve shaped so as to minimize separation of the supersonic jet from the first angled surface.

According to a further aspect, an upper surface of the plenum leading to the nozzle throat is a convex shape.

According to a further aspect, the diameter of the central lower surface is between 22 and

25mm.

According to a further aspect, the central lower surface diameter is about 4mm.

According to a further aspect, the radial extent between the nozzle outlet and the intersection between the first angled surface and the flat lower surface of the body is about 2mm.

According to a further aspect, the nozzle outlet is about 25 micron in height.

According to a further aspect, the nozzle outlet is about 25mm in diameter.

According to a further aspect, the device includes an annular upward step in the main body at the nozzle exit, such that the portion of the upper plenum surface at the nozzle exit is below the radially inner most portion of the first angled surface.

According to a further aspect, the intended supply pressure is about 5 bar.

According to a further aspect, a second angled flow directing surface is situated in the lower area of a plenum forming one side of an annular nozzle throat, and a pinde arrangement includes the lower central surface and an upper surface forming one side of an annular nozzle throat in the lower area of the plenum.

In a further aspect, the present invention may broadly be said to consist in a method of manufacturing a non contact lifting device for a gases supply pressure, the method comprising: designing an annular nozzle oudet to generate an annular supersonic gases jet, designing a flow impingement surface to carry the supersonic jet radially outward to end at or close to be not beyond a junction between the flow impingement surface and a lower flat lifting surface, determining an optimal diameter of a lower central lifting surface to maximise lift forces due to air entrainment by the supersonic jet, making a lifting device having the nozzle outlet, flow impingement surface and lower central lifting surface.

In a further aspect, the present invention may broadly be said to consist in a system for control of a non contact lifting device comprising a controller and one or more sensors, the controller has sensors collectively arranged to determine an approaching rapid loss of lift, and trigger adjustment of at least one parameter, the parameter being selected in order to modify the lifting force and prevent rapid loss of lift from the group including: fluid flow inlet pressure; fluid flow rate; pinde position relative to device underside; device diameter; decrease in load; redistribution of load where a plurality of devices are employed together in use. In a further aspect, the present invention may broadly be said to consist in a method for control of a non contact lifting device comprising identifying the approaching rapid loss of lift; adjusting at least one parameter, the parameter being selected in order to modify the lifting force and prevent rapid loss of lift from the group including: fluid flow inlet pressure; fluid flow rate; pintle position relative to device underside; device diameter; decrease in load; redistribution of load where a plurality of devices are employed together in use.

These and other objects, features and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings which are provided as an illustrative example of a preferred embodiment.

This invention may be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

The term "comprising" or variations such as "comprises", as used in this specification means "consisting at least in part of. That is to say when interpreting statements in this specification which include that term, the features prefaced by that term in each statement all need to be present but other features can also be present.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a cross-sectional view of one embodiment of the invention.

Figure 2 is an expanded cross-sectional view of a section of Figl according to one embodiment.

Figure 3 is graph depicting a pressure profile under the device according to one embodiment.

Figure 4 is a partial view of a CFD simulation of the improved lift generating mechanism of the device showing the location of the toroidal vortex and the location and length of the supersonic jet area according to one embodiment.

Figure 5 is a diagram demonstrating one embodiment of a system load sensor comprising a vibration sensor and accompanying controller.

Figure 6 is a CFD simulation of the fluid flow direction and relative speed according to one embodiment. DETAILED DESCRIPTION OF EMBODIMENTS

The preferred embodiments of the device and system of the present invention will be described in reference to the accompanying drawings. These embodiments do not represent the full scope of the invention, but rather the invention may be employed in other embodiments.

Figures 1 and 2 illustrate a non-contact device in accordance with a preferred embodiment of the invention. The non-contact device comprises a body (1) including a pinde (2) which may be moveable so as to enable adjustment of the nozzle throat gap (Fig 2, 20) and therefore distance (8) between the flat lower surface of the device body (5) and the lower pinde surface (7). At least one inlet port (3) supplies pressurized fluid and is preferably located to provide fluid flow to the plenum area surrounding the pinde (4) in perpendicular alignment with the central axis (18) of the body (1), said pressurized fluid being forced radially through the gap (12) between the pintie (2) and the flat lower surface of the device body (5).

By "pinde" we refer to a centrally located body that, together with the main body, defines an annular oudet port or nozzle at the bottom of the plenum. The pinde may be separable or adjustable relative to the main body. However, in some embodiments, the pinde may be integral and fixed relative to the main body.

Figure 2 illustrates an enlarged view of the nozzle throat section (6). A second angled slope (10) together with the pintle surface (11) are configured to cause a supersonic jet (17) to form at the pinde nozzle exit point (12).

The geometry of the first angled surface (9) is shaped so as to keep the supersonic jet attached to it.

The supersonic jet (17) entrains adjacent air between the body (1) and pinde (2). This entrained fluid flow in combination with the first angled surface (9) results in increased lifting efficiencies by creating a pressure drop (14) beneath the pintle area (7) and an extended pressure drop area over the flat lower surface of the device body (5).

Preferably the flat lower surface geometry of the device body (5) is symmetric in shape.

With regard to Fig 1, in a preferred embodiment the fluid is industrial grade compressed air. This is provided to the device (1) through the inlet port (3). In the preferred embodiment the inlet air pressure is set to 5 bar (absolute) at a flow rate of 100 litres per minute ANR. The air flows through the plenum (4) between the pinde (2) and the body (1) and exits through a 0.025mm gap (20) between the pintie nozzle (12) and flat lower surface of the device (5). The pinde diameter at the upper end of the pintie is 6mm and at the exit point (12) is 24mm. The outer diameter of the device(l) was 40mm. The resulting lift was 9.7N giving a lift/ flow ratio of 9.7(xl0-2). In a preferred embodiment the fluid inlet port (3) may be located offset from

perpendicular alignment with the centre of the pintle so as to create a tangential flow of pressurized fluid from the inlet port (3) to the plenum (4).

In an alternative embodiment the inlet port (3) is located vertically within the body (1) so as to provide fluid flow to the plenum (4).

In a further embodiment at least one inlet port(3) is located inline with the central axis (18) of the pintle (2). The fluid then flows into plenum (4) through vents in the pintle shaft (2).

The device (1) can be configured to vary performance characteristics at different flowrates.

In a preferred embodiment a 40mm device (1) produces a lift/ flow ratio of around 9.7

(xlO-2) from a flow rate of 100 litres per minute ANR at 5 bar absolute inlet pressure and produces adhesion of around 9.7N. With a fluid flow rate of 20 litres per minute ANR an adhesion force of around 2N might be produced. With a fluid flow rate of around 200 litres per minute ANR an adhesion force of over 20N might be produced.

As seen in Figure 2, the main body (1) includes a small annular step 30 adjacent the nozzle outlet 12. The small annular step 30 is at a transition between the second angled slope (10) and the first angled surface (9). The small step improves manufacturability of the lifter. The nozzle gap 20 is very small and the surfaces that form the nozzle gap must be carefully matched and finished. Providing an upward step 30 at the transition, with the nozzle surface portion of second slope (10) terminating lower than the radially inward end of the first angled surface, allows the nozzle surface to be machined and polished accurately without the risk of creating a downward step. Any downward step, with the nozzle surface portion ending above the inner radial end of the angled surface 9, would directly impinge on the jet flow from the nozzle substantially impairing performance of the lifter.

An increase in fluid flow rate may result from increasing the nozzle size, for example by increasing the exit gap between the pintle and the main body. Similarly, decreasing flow rate may be by decreasing this gap.

For reasons that will become apparent from discussions below, the varying jet conditions may lead to suboptimal performance, with the jet flow becoming subsonic further away from the transition (13) between the angled surface 9 and float lower surface 5.

Figure 3 depicts the actual pressure profile of a preferred embodiment. A static low pressure zone (14) corresponds with the region under the pintle (Fig 1, 7). An increased low pressure zone (15) occurs at the point where the toroidal vortex (22) is created by the supersonic jet (17) exiting the pintle nozzle gap (12). The pressure slowly recovers to atmosphere (16) at the end of the supersonic zone. The other pressure distribution shown (26) is an example pressure distribution of a similarly sized bernoulli chuck operated at the same fluid pressure and flowrate.

The following chart shows the measured radial static pressure distribution in the interfacial gap between the device and the surface of which the device would be attracted to. The interfacial gap was set at 0.3mm and the air pressure supplied to the device was 5 bar absolute. The zero radial point represents the centerline of the device, which is 40mm in overall diameter.

The upper curve (dotted) shows a 'typical' pressure distribution for a 'Bernoulli-type' lifter, as may be found published in both prior art and research literature. In this particular case, it was measured from an earlier device used in the gradual development of the device described in this document.

The low static pressure region is shown as the near-horizontal curve A and results from the gross air entrainment that occurs at the discharge jet. The position of the discharge jet is at the outer diameter of the pinde and can be seen at point B.

According to inventions herein, overall lifting performance of the device is improved by increasing the magnitude of the low pressure region, increasing the area (radial distance) over which the low pressure acts or both.

The improvements are illustrated on the chart by the solid line, which is the measured pressure distribution resulting from the optimized device incorporating these improvements.

Point C shows the location of the discharge jet, which is set at 24mm diameter, or 12mm radial distance (compared to 6mm for the development device), and the effect of extending the low pressure region further out is clearly seen. Additionally, the magnitude of the suction in the low pressure region is greater, with the relative static pressure line D at about - 10.5 kPa, compared to about - 8 kPa from the earlier device.

According to inventions herein, the lifting performance is improved by close attention to the design of the discharge jet and the wall geometry immediately downstream of it. Increasing the diameter of the pinde of a prior art device, and with it the radial location of the discharge jet, will not by itself yield these benefits. Holding all other factors constant, an increase in pinde diameter may diminish the entrainment effect and the magnitude of the low pressure region may reduce as a consequence.

For the given supply pressure of 5 bar, the disclosed design optimizes the jet entrainment effect to set the magnitude of the low pressure region D. Secondly, the optimal location for the discharge jet will set the radial extent C of the low pressure region. These activities may thus be described as working to make the low pressure region 'deeper and wider'. This is a multiparameter optimization process that was performed iteratively for the intended 5 bar supply pressure. The inventors found that with a supersonic flow jet extending to end close to the interfacial gap transition 13, the pintle diameter could be dramatically increased relative to prior art devices without compromising the depth of the pressure trough below the pintle.

A 5 bar absolute supply pressure corresponds with the most commonly available industrial air supply pressure over built in compressed air distribution systems.

The optimized pintle lower surface diameter is about 24mm. The diameter pintle lower surface diameter is preferably above 22mm. The pinde lower surface diameter is preferably below 25mm.

The width of the entrainment zone (The radial distance between the nozzle outlet 12 and the transition 13) is optimized so that the gases jet becomes subsonic at or close to, but not beyond, the transition 13. For the 5 bar supply pressure the radial extent of this zone is preferably about 2mm.

The oudet nozzle is preferably shaped and sized to provide a supersonic gases jet at the outlet of the nozzle for the design supply pressure. For the 5 bar supply pressure, an annular nozzle tapering to about 25 micron width is preferred. This annular nozzle oudet is preferably about 24mm in diameter, and may be preferably between 22mm and 25mm in diameter.

Alternative optimizations could be made for other supply pressures. This would involve optimizing the jet aperture 2 and attachment surface 9 such that the gases jet 17 becomes subsonic at or close to the interfacial gap transition 13. Then the pintle diameter (and jet location diameter) could be iteratively optimized until the model or test results indicate a maximum diameter without compromising the depth of pressure under the pinde. For higher supply pressure, the inventors expect the optimal diameter to increase from 24mm. For lower supply pressures, the inventors expect the optimal diameter to decrease from 24mm.

According to embodiments of the present invention:

. Major contribution to lift generation is viscous flow entrainment, in addition to the better- known Bernoulli principle

2. Optimal lift is achieved by balancing three principles:

a. Achieving maximum flow entrainment from the available air supply power

b. Maximising the area over which the flow entrainment acts, since lift force is proportional to area

c. Preventing entrained air from returning underneath the device, which compromises the low pressure region and reduces lift force

3. Viscous flow entrainment is enhanced by increasing flow velocity

4. The device is preferably configured in such a way as to create supersonic flow; further enhancing viscous flow entrainment 5. The pintle diameter is increased to thereby increase the area over which flow entrainment acts. There is an optimal pintle diameter, since the maximum available flow velocity for a given air supply power will begin to reduce and entrainment will become compromised

6. The termination of the supersonic flow region is configured in such a way as to minimise the return of air underneath the device to optimise lift.

The solid line in Figure 3 depicts the pressure distribution under the device (Figure 1).

The low pressure trough (Fig3, 14) can be controlled. By adjusting the gap (Fig2, 12) the optimal supersonic region is created to entrain surrounding fluid. This enhances the entrainment effect and sets up a stronger toroidal vortex zone. The steepness of the toroidal vortex zone is influenced by the length of the first angled surface (9). The location of the toroidal vortex is influenced by the pintle diameter (7)

The steepness and location of the recovery zone (Fig 5, D) can also be controlled. By increasing the diameter of the lower surface of the pintle (Figl, 7) the recovery zone can be extended radially. The optimal diameter for the preferred embodiment was 24mm for a device with an outside diameter of the lower surface (5) of the device (1) being 40mm.

Figure 4 depicts the supersonic jet zone (17) according to the preferred embodiment. In particular the termination of the supersonic jet zone (17) coincides with the intersection (13) of the first angled surface (9) and the flat lower surface (5).

Figure 5 depicts a sensor (24) and control system (25) to monitor the load on the device (1). In the preferred embodiment at least one sensor (24) is attached to or in near contact with the device (1) so as to sense when the adhesion force between the undersurface of the device (5, 7) and the article or opposing surface (23) are approaching a rapid loss in lift point, whereby the at least one sensor (24) triggers a change in parameters to prevent said rapid loss. Parameters which may be controlled to prevent rapid loss include one or more of: a change to the fluid pressure at the inlet port (3); a change in position of the lower surface of the pinde (7) relative to the flat lower surface of the device (5) by means of adjusting the pintle (2) with an actuator (not shown) to modify the fluid flowrate; provision of an adjustable diameter of the flat lower surface of the device body (5) so as to adjust the outer diameter of the device (not shown).

Figure 6 depicts a CFD simulation of the internal fluid domain of the device (1) showing the fluid flow path from the inlet (3) to the outer diameter of the device (1) showing the radial flow of the fluid after it passes the nozzle exit point (12), adheres to curved deflection surface (9) and exhausts to atmosphere between lower surface (5) and the opposing surface (23).

Claims

CLAIMS:

1. A non contact lifting device comprising:

a body including a flat lower surface radially outward of a first angled impingement surface,

a plenum with an outwardly facing annular outlet including a nozzle throat

at least one fluid inlet port communicating gases to the plenum; and

a central lower surface below the plenum,

wherein the nozzle throat geometry and fluid pressure supplied in use through the fluid inlet port cause a supersonic gases jet to exit the nozzle throat in a radially outwards direction into an area below the first angled impingement surface;

and wherein the geometry of the first angled surface in a region between the nozzle throat and intersection of the first angled surface and the flat lower surface of the body, maximizes the entrainment effect of gases under the central lower surface by carrying the gases downstream in a radially outwards direction and setting up a toroidal vortex in the area under the first angled surface.

2. A non contact lifting device as claimed in claim 1 wherein the length of the first angled surface between the nozzle throat and the intersection of the first angled surface and the flat lower surface of the body is a function of the length of the supersonic jet, such that the jet becomes subsonic at or close to, but not beyond, the intersection of the first angled surface and the flat lower surface of the body.

3. A non contact lifting device as claimed in claim 1 or claim 2 wherein the first angled surface between the nozzle throat and the intersection of the first angled surface and the flat lower surface of the body is a concave curve shaped so as to minimize separation of the supersonic jet from the first angled surface.

4. A non contact lifting device as claimed in any one of claims 1 to 3 wherein an upper surface of the plenum leading to the nozzle throat is a convex shape.

5. A non contact lifting device as claimed in any one of claims 1 to 4 wherein the diameter of the central lower surface is between 22 and 25mm.

6. A non contact lifting device as claimed in claim 5 wherein the central lower surface diameter is about 4mm.

7. A non contact lifting device as claimed in any one of claims 1 to 6 wherein the radial extent between the nozzle outlet and the intersection between the first angled surface and the flat lower surface of the body is about 2mm.

8. A non contact lifting device as claimed in any one of claims 1 to 7 wherein the nozzle oudet is about 25 micron in height.

9. A non contact lifting device as claimed in any one of claims 1 to 8 wherein the nozzle oudet is about 25mm in diameter. 0. A non contact lifting device as claimed in any one of claims 1 to 9 including an annular upward step in the main body at the nozzle exit, such that the portion of the upper plenum surface at the nozzle exit is below the radially inner most portion of the first angled surface.

11. A non contact lifting device as claimed in any one of claims 1 to 10 wherein the intended supply pressure is about 5 bar.

12. A non contact lifting device as claimed in any one of claims 1 to 11 wherein a second angled flow directing surface is situated in the lower area of a plenum forming one side of an annular nozzle throat, and a pintle arrangement includes the lower central surface and an upper surface forming one side of an annular nozzle throat in the lower area of the plenum.

13. A method of manufacturing a non contact lifting device for a gases supply pressure, the method comprising:

designing an annular nozzle oudet to generate an annular supersonic gases jet, designing a flow impingement surface to carry the supersonic jet radially outward to end at or close to be not beyond a junction between the flow impingement surface and a lower flat lifting surface,

determining an optimal diameter of a lower central lifting surface to maximise lift forces due to air entrainment by the supersonic jet,

making a Hfting device having the nozzle oudet, flow impingement surface and lower central lifting surface. 14. A system for control of a non contact lifting device comprising: a controller and one or more sensors, the controller has sensors collectively arranged to: determine an approaching rapid loss of lift, and

trigger adjustment of at least one parameter, the parameter being selected in order to modify the lifting force and prevent rapid loss of lift from the group including: fluid flow inlet pressure; fluid flow rate; pintle position relative to device underside; device diameter; decrease in load;

redistribution of load where a plurality of devices are employed together in use.

15. A method for control of a non contact lifting device comprising:

identifying the approaching rapid loss of lift;

adjusting at least one parameter, the parameter being selected in order to modify the Hfting force and prevent rapid loss of lift from the group including: fluid flow inlet pressure; fluid flow rate; pintle position relative to device underside; device diameter; decrease in load;