WO2001060638A1 | 2001-08-23 |
JPS61254436A | 1986-11-12 | |||
US20020130524A1 | 2002-09-19 |
CLAIMS: 1 A Bernoulli type non-contact adhesion pad comprising a body including a pad area and comprising a pin, means for coupling the pad to a fluid supply for introducing pressurised fluid flow to a pad area surrounding the pin and over the pad area, a profiled undercut in said pad area comprising an angled ramp to control in use pressure distribution and maintain the pin at a distance which avoids contact with a surface, said pin including a sharp trailing edge at a point where high \ elocity fluid exits around the pin to thereb) in use additionally entrain adjacent fluid to create a change in static pressure which increases the pressure difference across the device in the region between the surface and the pad area 2 An adhesion pad according to claim 1 arranged so that in use the high velocity fluid flow exits the trailing edge in a radial direcuon wheie the gap between the pin trailing edge and the undercut intersect 3 An adhesion pad accoiding to claim 1 comprising vanes or grooves fabricated into the pin oudet to control the direction in which in use high \ elocity fluid exits the sharp trailing edge of the pin oudet 4 An adhesion pad according to any one of claims 1 to 3 arranged so that in use piessuπzed fluid can be introduced to the gap between the mam bod) and pin in such a way as to introduce a tangential flow component into the pressunzed fluid stream 5 A method of lmpioving the lifting force of a Bernoulli-type lifting device comprising establishing a pressurized fluid flow in a device containing a body and pin so that said pressurized fluid flow is directed to an oudet of the pin, a gap in the device between a trailing edge, said pin, and a profiled undercut of an adhesion pad being optimized to entrain adjacent fluid into high velocity fluid flow CM ting the outlet of said pin theieby cieating a low pressuie legion which increases lifting foice 6 A method according to claim 5 whcicin the piessuiizcd fluid flow is a compiessed air flow 7 A robot device comprising at least one Beinoulli-tjpe non contact adhesion pad which in use can generate sufficient attraction force to maintain adheience to said surfaces, with a force distribution to pressure ratio sufficient to enable adherence to sloping, vertical oi inverted smooth and non-smooth surfaces 8 A robot device capable of adherence to and locomotion along a non-horizontal surface, comprising one or more Bernoulli-type non-contact adhesion pad(s) which in use generate sufficient attraction force to maintain adherence to the surface 9 A robot device according to claim 8 also comprising at least one contact device for maintaining the device at a set position on the surface 10 A robot device according to any one of claims 7 to 10 including means for connecting a pressurized fluid supply to the device through a tether 11 A robot device according to any one of claims 7 to 9 including an on board pressurised an supply 12 A iobot device accoidmg to claim 9 wheiein the at least one contact device also ides a source of locomotion along the surface 13 A robot device according to claim 9 wherein the at least one contact device is a wheel 14 A robot device according to claim 13 including a motoi arranged to drive the at least one wheel 15 A iobot device according to any one of claims 8 to 13 compiismg contiol devices and/or instrumentation attached to the device 16 A iobot device according to any one of claims 7 to 15 and wherein the Bernoulli-type non contact adhesion pads are according to any of claims 1 to 4, 16, oi 17 17 A Bcinoulli-type non-contact adhesion pad compiising a pad aica which includes an outer section of the pad area and an inner section of the pad aiea which is undeicut relative to the outer section, at least one aperture in the inner section of the pad aica for introducing a pressuπsed fluid flow from the apertuie in use between the pad area and a surface for non- contact adhesion of the pad to the surface, an element extending from the aperture beyond the periphery of the aperture, but not the outer section of the pad area, so that the flow of fluid from the aperture is between and around the element and the periphery of the aperture, the element including an edge around the element at or beyond the aperture. 18. A Bernoulli-type non-contact adhesion pad according to claim 17 wherein said inner section of the pad area slopes in an annular ramp from the aperture to the outer section of the pad area 19. A surface adhesion capable of non-contact adhesion to a non-horizontal surface comprising at least one Bernoulli-t) pe non-contact adhesion pad according to any one of claims 1 to 4, 17 and 18. |
FIELD OF THE INVENTION
The invention pertains to non-contact lifting devices, an adhesion mechanism, and wall climbing robot device based on the Bernoulli principle.
BACKGROUND OF THE INVENTION
Bernoulli Lifting Devices
Lifting devices based on the Bernoulli principle have been employed as non-contact lifting mechanisms for applications such as semi-conductor wafer handling, food handling and materials conveying.
End effectors such as the Bosch Rexroth NCT series lifters (see www.boschrexroth.com/pneumatics) are employed as non contact pick and place devices on materials handling robots such as the ABB Flexpicker.
The degree of lifting force for such devices based on the Bernoulli effect is a function of flow rate, air pressure and position in the flow field. US patent 6,601,888 provides a description of factors determining the magnitude of lift generated and a description of approaches known in the art.
Existing devices such as the Rexroth NCT 40 device produces 2N of lifting force at a flowrate of llOl/min using 5 bar operating pressure. The Rexroth NCT 60 device produces a lifting force of 6N at 5 bar operating pressure but requires 2101/min airflow rate to achieve this force.
Wall Climbing Devices
Robotic wall climbers have a multitude of uses, for example they can replace humans to perform dangerous tasks such as inspections, maintenance and cleaning in hostile environments, and are used in non-destructive testing applications. Suction adhesion and magnetic adhesion are the most common attachment mechanisms for wall chmbmg robots
Suction adhesion robots typically carry an onboard pump to create a vacuum inside cups which are pressed against a wall or ceiling. Effective suction adhesion is dependent on a smooth impermeable surface to create enough force to hold the robot.
Magnetic adhesion has been implemented in wall climbing robots for specific applications such as nuclear facility inspection. This can be a very reliable technology but requires that the surface allows magnetic attachment.
Other novel adhesion mechanisms such as dry adhesion using synthetic fibrillar adhesives exist, however have limitations for smooth vertical wall applications.
Vortex adhesion mechanisms are also known in the art, as are electrostatic adhesion mechanisms.
SUMMARY OF INVENTION
An object of the present invention is to provide an improved or at least alternate e Bernoulli-type non contact lifting mechanism and/or wall climbing device.
According to one aspect of the present invention, there is provided a Bernoulk-t\ pe non-contact adhesion pad comprising: a bod\ including a pad area and comprising a pm; means for coupling the pad to a fluid supply for introducing pressurised fluid flow to a pad area suriounding the pm and over the pad area; a profiled undercut in said pad area comprising an angled ramp to control in use pressure distribution and maintain the pin at a distance which avoids contact with a surface, said pin including a sharp trailing edge at a point where high velocity fluid exits around the pm to thereby in use additionally entrain adjacent fluid to create a change in static pressure which increases the pressuie difference across the device in the region between the surface and the pad area
In this aspect the invention may also be said to comprise a Bernoulli-type non-contact adhesion pad comprising a pad area which includes an outer section of the pad area and an inner section of the pad aiea which is undercut relative to the outer section, at least one aperture in the inner section of the pad area for introducing a pressunsed fluid flow from the aperture in use between the pad area and a surface for non-contact adhesion of the pad to the surface, an element extending from the aperture beyond the penpher ) of the aperture, but not the outer section of the pad area, so that the flow of fluid from the aperture is between and around the element and the periphery of the aperture, the element including an edge around the element at or beyond the aperture.
Preferably the pressurized fluid flow exits the trailing edge of the pin in a radial direction where the gap between the pin insert's trailing edge and the undercut intersect.
Alternatively features such as vanes or es can be designed into the pin to control the direction in which fluid exits the sharp tiailing edge of the nozzle.
It is also possible to introduce the pressuuzed fluid to the gap between the main body and pin insert in such a way as to introduce a tangential flow component into the incoming fluid stream.
Preferably the pressurized fluid supply is a compressed air supply.
According to a second aspect of the piesent invention, there is piovided a method of improving the lifting force of a Bernoulli-type lifting device comprising establishing a pressurized fluid flow in a device containing a body and pin so that the pressurized fluid flow is directed to an outlet of the pm, a gap in the device between a ttailing edge, said pm, and a profiled undercut of an adhesion pad being optimized to entrain adjacent fluid into high velocity fluid flow exiting the outlet of said pin thereby creating a low pressure icgion which increases lifting force.
According to a third aspect of the present invention, there is provided a robot device comprising at least one Bernoulli- type non-contact adhesion pad which in use can generate sufficient attraction force to maintain adherence to said surfaces, with a force distribution to pressure ratio sufficient to enable adherence to sloping, veitical oi lnvcited smooth and non-smooth surfaces.
The device may be able to carr j a payload on sloping, vertical oi inverted surfaces where conditions range from smooth to rough, and the device may be able to negotiate over cracks and small gaps and porous surfaces Preferably the attraction force achieved fiom each adhesion pad used in the device is of a ratio producing at least 6N, where the airflow rate is no higher than 521/min, and the operating pressure is no greater than 5 bar.
Preferabl) multiple adhesion pads are utilized in the device
The device can be connected to a local pressure and power supply.
Alternativel) the device can contain an onboard pressurised fluid supply.
Preferably an onboaid pressurized fluid supply is achieved with a batter ) ' and air compressor
Preferablv the device is modular so that a wide range of control devices and instrumentation can be attached specific to the application chosen.
According to a forth aspect of the present invention, there is provided a robot device capable of adherence to and locomotion along a non-horizontal surface, comprising one or more Bernoulli- t ) pe non-contact adhesion pad(s) which in use generate sufficient attraction force to maintain adherence to the surface
As the impioved adhesion pads create suction without touching the wall, at least one contact device which creates high friction is preferable to avoid sliding off the surface
The contact points are also preferable for movement and manoeuvrability of the device.
Preferablv wheels are used to provide locomotion. Wheels allow for high and fast manoeuvres. Faction coefficients are optimized for the surfaces taigeted. Servo motois arc attached to the wheels
Symmetrical alignment of the adhesion pads and wheels allows the iobot to climb in all diiections
Alternatively locomotion can be achieved with for example feet or tracks instead of wheels BRIEF DESCRIPTION OF DRAWINGS
The invention is further described with reference to the accompanying drawings, in which
Fig 1 is a graph showing force and pressure distribution in an experimental device
Figs 2a-c shows a series of edge designs for the outer diameter of the pad of a device of the invention
Fig 3 is a graph of maximum force to pressure of three experimental devices.
Fig 4 is a graph of flow rate obtained with diffeient pressures with three experimental devices
Figs 5(a) and (b) are cross-sectional views of two embodiments of attachment devices.
Fig 6a is a cross-sectional view of an adhesion pad of an embodiment of the invention, Fig 6b and 6c showing parts in expanded detail.
Fig 7 is a top view of one embodiment of a wall climbing robot of an embodiment of the invention
Fig 8 is a graph of maximum attraction forces of an experimental pad on different surfaces.
Fig 9 is a graph of dependence of attraction force on surface roughness.
Fig 10 is a graph of dependence of attraction force on clearance gap distance
Fig 11 is a graph of dependence of attraction force on orientation angle of a glass surface
Fig 12 is an illustration of an adhesion pad crossing a gap.
Fig 13 is a graph showing dependence of attiacuon force on gap size DETAILED DESCRIPTION OF EMBODIMENTS
The preferred embodiments of the apparatus 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.
The invention makes use of Bernoulli-type lifting force. The magnitude of Bernoulli lift is commonly agreed to be dependent on several factors such as flow rate of the fluid being supplied b) the positive pressure fluid source, the density of the fluid, the diameter of the pickup shaft and the pickup opening, the proximity of the pickup surface relative to the object surface and the pressure of the surrounding medium, extent to which the positive pressure fluid can maintain a pattern of laminar flow as it passes through the space between the pickup face and the object, as described in US patent 6,601,888.
Fig 6 depicts a device and method which demonstrates sufficient foice force to piessure ratio to provide the lifting force necessary to adhere a device to a sloping, vertical or inverted surface The adhesion pad 1 contains a pmtel 2 which is located to provide a specific gap 8 to allow pressurized fluid flow, which enters the device 4 to exit the pad through nozzle oudets 7 which have specific dimensions as to optimise the fluid velocity exiting the nozzle 7 and the pad 1. The outer diameter 10 of the pad 1 is optimized, including edge design 11 for the specific application required and contains a ramped undercut 7 which contributes to control of the pressure distribution and also safeguards the pin 2. The lifting force may be augmented with other fluid dynamic phenomena to enhance the fluid pressure difference that holds the pad to a surface. In particular, at a sharp trailing edge of the pmtel nozzle 12 the radial flow of high velocity air exiting the pin nozzle entrains fluid flow from the underside of the pin area creating a low pressure region.
Fig 5b depicts a device similar to Fig 6 with the exception that the bottom section 21 is detachabh connected in order to allow for easy lemoval and substitution of bottom plates for specific applications.
Fig 7 depicts a wall climbing robot device which employs the adhesion pad design of Fig 6 in ordei to adhere to sloping, vertical and inverted surfaces The wall climbing iobot contains two adhesion pads of the design depicted in Fig 6 each equally splitting the 1001/min airflow supplied to the device Servo motors and wheels aie added to facilitate positioning and locomotion along vertical surfaces
The invention is further illustrated by the following description of experimental work, given by way of example and without intending to be limiting
Outlet design
In a Bernoulli lifter, an increase in force results from an increase in fluid flow velocity through the lifter When the flow is regulated befoie reaching the nozzle, the gap at the nozzle is not the smallest conduit of the system The highest velocity of the fluid is reached in the smallest conduit of a pipe system due to the same mass flow in ever) cross section Therefore, the velocity at the nozzle decreases because of the flow vah e ieducing the flow The highest force is created by the highest fluid speed between de\ ice and wall To ieach the maximum fluid speed at the nozzle and consequently between device and wall, the Bernoulli device always has to run with the highest possible flow rate in a working pressure Theiefore, the device has to be designed considering the specifications of the pressure supph
Size and edge design
It is known that the stream \ elocity slows down with the radius of a Bernoulli pad, hence the static pressure in the gap increases with the radius 1 he achieved total force only increases slighdy with increase in outer diameter of the pad, but the an gap between the pad and surface becomes narrower, and tilting at of the pad with iespect to suifaces becomes more common A robot should be able to climb surfaces such as walls, so considerations for size and force have to be made
A sharp edge on the Bernoulli pad as shown in Fig 2a also increases tilting Therefore, a rounded and an angled edge were tested as shown in Figs 2c and 2b Best performance on surfaces was achieved with the rounded edge Foi the angled and rounded edges, compared to the sharp edge theie was a verv small force reduction, depending on the dimension of the edge alteiation The air stream noise is also ieduced b \ the iounded edge Flow Regulated Attachment Mechanism
Attachment mechanisms as shown in Fig 5 were made of top and bottom parts 20 and 21 connected with screws (not shown) and a sealing ring (not shown) to avoid loss of air pressure. The top part was connected at 22 to an air supply, while the bottom part comprised compression air outlets 23. The two-part configuration allowed changes of the bottom part for different experiments and fine-tuning the airflow to suit a specific application, and allowed tailoring attraction force and distribution by changing the bottom part only.
In one attachment as shown in Fig 5a the bottom part 21 comprised seven symmetrically arranged holes and three angled holes 23 with 60 degrees from the vertical direcDon.
Anothei attachment as shown in Fig 5b had only one hole in the middle and a tapered outlet. A matching tapered pm 25 was placed in the hole and screwed into the top part of the device, which deflected the air flow out of the hole radially towards the outer edge of the device This provided a smooth conduit for air flow guidance as well as additional flexibility m regulating the ail flow via screwing in or out of the pm. The airflow rate could be changed b ) ad j usting the pin position
In both cases the pad was made of lightweight aluminium to reduce the weight of the device
Adhesion Pad Design
With reference to a cross section of the body of the pad shown in Fig 6a, the pad comprises a pad undercut shown enlaiged in Fig 6b and pin insert shown separately in Fig 6c, the main body 1 is one part with the pin 2 screwed in 3 at the middle. A threaded inlet connection 4 to the pressurised air supply (not shown) was provided. The pad of Fig 6a was mounted to the wall climbing robot of Fig 7 with two threads on the top 5.
The outer diameter of the nozzle 6 was 6 mm. The resulting nozzle gap 7 between the pin 2 and the main body 1 to achieve the desired flow rate of 50 1/min at 5 bars for a diameter of 6 mm was onl) 0.10 mm (and could be made much smaller with a bigger pin 2)
The gap 8 between the pin 2 and the main body 1 was ensured by a tight tolerance at the pm 2 and pin support 3 in the main body 1. A flat stopper 9 was included in the construction of the pin 2 which exactly fit into the 5 mm diameter drilling of the body 1 There was no air flow disturbance at the outlet 7. The pin with the stopper is separately shown in Fig 6c.
The undercut 9 - see Fig 6b - safeguards the pin 2. Because the mam body 1 was closer to the surface (not shown) than the pin 2, the pin 2 avoids being in contact with the surface (not shown). As such, potential scratching of the pin 2 and damage of the nozzle system 12 is prevented.
The angled ramp of the undercut 9 serves as a guide for oudet air It reduces the clearance distance between the surface (not shown) and the pad so that the air speed reduction due to die increasing radius was slowed down. This otherwise results in a slower increase of pressure and likewise a decrease of attraction force. In one experimental pad the outer diameter of the main body 10 was reduced to 45 mm including a rounded edge with a radius of 3 mm This reduction of diameter was a trade off between attraction force and the ability to compensate for tilting. With the shghdy reduced outer diameter 10 and the iounded edge 11, the pad could also accommodate small tilts which may be encountered when the robot (not shown) transverses on an uneven surface (not shown)
Improved Lifting Force
Lifting force has been increased by augmenting the Bernoulli effect with other fluid dynamic phenomena to enhance die air pressure difference that holds the pad to a surface
In particular, at the sharp trailing edge of the pin insert nozzle 12, the radial flow of high velocity air exiting the pin nozzle entrains fluid flow from the underside face of the pin creating a low pressure region
Attraction Force on various surfaces
Two pads as described with reference to Fig 6 were constructed and tested 7. A flow of 51 1/min at 5 bars was used Fig 3 shows the lifting force to pressure comparing the device of Fig 6 — filled squares with the device of Fig 5a — onfilled diamonds, and a flow rate setting of 50 1/min and die device of Fig 5b — filled triangles The flow rate behaviour of the devices over pressure is shown in Fig 4. In all three cases, the attraction forces increase proportionally with the piessuie The device of Fig 5b offered a higher force than that of Fig 6 at the same pressure At the piessuie of 5 bars, the maximum force of 6 4 N was achieved on a glass surface
To use the attachments for wall climbing robots, it was desired to have a reliable adhesion on different surface materials and surface conditions Therefore, many experiments were carried out on metal, plastic and wooden surfaces, and finally expanded to different grained sandpapers and other materials with results shown in Fig 8 The attraction force was shown to be dependent on surface roughness as shown in Fig 9
Attraction force was also shown to be dependent on the clearance distance between the pad and the surface, as shown in Fig 10, and the orientation angle to the suiface as shown in Fig 11
Tests were also conducted with simulated cracks on the suiface The le&ults aie shown in Fig 12 and Fig 13
Wall-Climbing Robot
An air supplv system delivering a pressure of 5 bars and a permanent flow iate of 120 1/min was used A robot as shown in Fig 7 was constructed with two pads 70 of the design shown in Fig 6 For each pad to reach 50 to 60 I/mm flow rate equally, the most important design consideration is the noz7le opening In the prototype robot, the nozzle with 6 mm diameter and a very precise opening gap of 0 10 mm achieved equal air flow between two pads The weight of one suction pad, made of aluminium, was 19 grams The tube fitting for the pressure supply weighed 4 grams One pad operating with an air flow of 51 - 52 1/min at a pressure of 5 bars created a force of 6 0 N 1 he attraction force generated was relatively consistent for diffeient surfaces
As the Bernoulli- type pads are non-contact, and flow over an air cushion, the robot needs contact physical points to iemain in a controlled position on a wall by relying on the friction force, such as one oi mote wheels 71 din en by DC motors 72 With a high friction coefficient wheel mateiial, the faction force is high enough to stabilise the robot and am onboaid tools on a Λ ettical wall The prototype robot was able to climb on a \ anet) of surfaces. Best results were achieved with a combination of a rubber with a friction coefficient of 0 74 on glass with a thin strip of Velcro which supports climbing on cloth and vet) raw surfaces. The wheel(s) can be changed to the best material(s) for the desired application. For different surfaces, wheels can be changed on-site.
Stability of the prototype robot was achieved through two Bernoulli suction pads in the front and at the back of the robot at a distance of 180 mm. These non-contact devices self-place them in a distance of about 0.5 mm of the wall The whole robot was designed symmetrically in two axes, so that the stability still maintains when the robot is climbing with the head down. The main body was made out of a plastic bar 73 with a T-profile to reduce the total weight and to achieve high stiffness To get the best transfer of the suction force to the contact points, a lightweight suspension system for the wheels is preferably provided. The motor(s) and wheels may be mounted on a thin and flexible aluminium beam, which is elastic enough to act as a suspension system.
The prototype wall climbing robot is shown in Fig 7 Its total length was 224 mm and its width was 156 mm. The robot was dnven using two gear-head micro motors. One drive train had a weight of only 38 grams. In total the robot weighed 234 grams and was able to lift an additional weight of 500 grams on a vertical concietc suifacc as well as on a glass surface. It can move in all directions: forward, backward, left, light, and upside down
The design achieved 12 N for a robot weighing 234 grams, with the force/weight ratio being as
In addition to reliable adhesion on various surface another advantage of the device is that it is "self-cleaning" of the surface. When the robot climbs on a dirty and dusty surface, the air stream cleans the surface and for example so picpaies it for surface inspection using an onboard measuring instrument.
A standard high pressure supply or a compressor can be used Batteries for instruments and motors can be mounted on boaid The robot can be steered by a remote control or may be arranged to autonomously navigate using onboard sensors and controllers. Because of the simple but very effectrve wheeled locomotion and only two suction pads of the prototype, a simple contiol system can be emplo ) ed to steer the movement The non-contact adhesion method opens up great potential for wide industrial adoptions such as structural inspection, surveillance, part transporting in bio-medical, inspection, and tank welding
Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the accompanying claims