WO2013074626A1 - Smoothly adjustable tablet stand - Google Patents

Abstract

A smoothly adjustable table stand comprises a bent vertical pole, a horizontal boom and a gripper for holding a tablet computer. The bent vertical pole allows for a shallow arc for vertical adjustment of the position of tablet computer while at the same time allows for a tight arc for horizontal movement of a tablet away from a user. The horizontal boom may be attached to the top of the bent vertical pole by a large diameter T joint. The large diameter T joint comprises a first friction plate, a second friction plate, a lubricant and a means for urging the friction plates together. The lubricant is disposed between the friction plates. The gripper may be attached to the distal end of the boom by a magnetic ball joint. The magnetic ball joint may comprise a lubricant disposed between the ball and socket.

Description

SMOOTHLY ADJUSTABLE TABLET STAND

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of US provisional patent application "Tablet Floor Stand", serial number 61/559,291, filed November 14, 2011. The entire contents of said application are incorporated herein by reference.

TECHNICAL FIELD

The invention(s) described herein relate to stands for holding tablet computers or other objects. Tablet computers include iPad® by Apple Inc. and Kindle® by Amazon.com, Inc.

BACKGROUND OF THE INVENTION

Tablet computers are popular hand held computing and display devices. Many users, however, would like to have stands that would hold their tablet computers in a fixed position for an extended period of time. The situations where a user might like his/her tablet held include, but are not limited to:

• When lying in bed watching a movie on the tablet;

• While sitting in a chair reading a book on the tablet; and

• While standing at a kitchen counter looking up a recipe on the tablet.

In each of these situations, the user would assume a particular position (e.g. lying down, sitting, down, or standing at a counter), move his/her tablet into place, engage in his/her activity, and at the conclusion of the activity, move the tablet out of the way so that the user can proceed to the next activity. It is desirable to have a stand for holding a tablet, therefore, where the position of the tablet can be smoothly adjusted from one location and orientation to another. By "smoothly adjusted", it is meant that there is minimal jerking motion of the tablet as its movement is initiated, that the motion is smooth as the tablet continues its movement, and that the tablet remains in a desired position and orientation indefinitely under its own weight after motion is stopped. Jerking motion can occur when the static friction of initial motion is significantly higher than the dynamic friction of continued motion.

Static friction is known as stiction. As used herein, "absolute stiction" is the absolute value of the stiction. As used herein "net stiction" is the difference between absolute stiction of initial motion and the dynamic friction of continued motion. A desired attribute of a tablet stand, therefore, is one which has high enough absolute stiction so that a tablet will remain in place once it is positioned and a low enough net stiction such that there is minimal jerking of the tablet as motion is initiated. The inventive tablet stands described herein have this combined property and are referred to as "smoothly adjustable tablet stands".

Tablet stands in the past have attempted to achieve smooth adjustment through a minimization of torque about all joints. An exemplary prior art stand is illustrated in figures 1A and IB. These are redrawn figures from US patent publication US2011/020448 Al, "Tablet Computing Device System" by Springer et al (Springer). Said publication is incorporated herein by reference. Figure 1A herein corresponds to Figure 15 of Springer. Figure IB herein corresponds to Figure 8B of Springer. Figure 1A illustrates an overall view of the Springer tablet holder. Figure IB illustrates a view of the back of the housing used to hold a tablet computer.

Referring to figure 1A, the Springer tablet stand 100 comprises a power cord 101, base 102, vertical pole 104, T joint 106, boom 108 and tablet housing 110. The base has a depth 105, width and length 103 and weight sufficient to provide stability to the stand under the weight of tablet 112 mounted in the housing at the end of the boom. A counter weight 118 is provided on a rear extension of the boom 123. The length of the rear extension is about ½ of the forward length of the boom 122. A suitable counter weight would be twice the combined weight of the housing and tablet. Springer gives an exemplary counter weight of 1,362 gm (3 lbs) for a tablet computing device weighing 726 gm (1.6 lbs). The counter weight minimizes the net torque on the T joint and thus reduces the absolute stiction required ("tension on the Chicago bolt" per Springer) to keep the tablet in place when its position is set. Springer, however, makes no provision to reduce net stiction. A person of ordinary skill would expect noticeable jerking when motion of the tablet is initiated. A person of ordinary skill would also expect to have to change counter weights if a lighter or heavier tablet were used.

The use of the straight vertical pole 104 in Springer can render moving the tablet in and out of a desired position awkward. The forward length of the boom 122 dictates the arc 124 that the tablet traverses when it moves up or down. This arc is significantly bowed in Springer. This would make vertical adjustment of the tablet awkward since the tablet would move side to side. A user would have to change his/her position if the tablet height were adjusted. The forward length of the boom also dictates the radius 126 of horizontal swing 128 of the tablet when a user wishes to push the tablet out of the way when an activity is completed. This swing is fairly large in Springer so a lot of clearance is required for the stand. An improved stand over Swinger would be one where the arc of vertical motion was shallower and the arc of horizontal motion were tighter.

Figure IB illustrates the tablet holder 140 of Springer. The holder comprises a main body 142, a hinged side 144, a socket 146 for receiving a ball 148 at the end of the boom 150 and side walls 152 and fingers 154 (Figure 1A) for securing a tablet inserted therein. The back wall 156 of the holder is relatively flat. Thus when a tablet is inserted into the holder and the hinged side is closed, the tablet is held in a firm position with its center of mass near the center of the ball. Having the center of mass of the tablet near the center of the ball helps reduce torque about the pivot point and reduces the absolute stiction needed to hold the tablet in place once its orientation is set. It does not address the issue of net stiction, however. Thus a person of ordinary skill would expect noticeable jerking of the tablet when changing its rotational orientation.

DISCLOSURE OF INVENTION

The disclosure of the invention is provided as a guide to understanding the invention(s) described herein. It does not necessarily disclose the most generic embodiment(s) of said invention(s).

As used herein, the term "about" or its synonyms means +/- 10% of a given value unless specifically indicated otherwise.

An exemplary embodiment of a smoothly adjusting tablet stand is illustrated in figure 2A. The stand comprises a base 202, compact stabilizing weight 208, bent vertical pole 210, large diameter T joint 220, boom 222, and spring gripper 230.

The base has a relatively thin depth 206 and standard width 204 relative to the Springer design. The base may be made of metal or other durable material. A suitable depth is about 1.3 cm. A suitable width is about 30 cm. A suitable shape is disk shaped. Other shapes, such as square, rectangular, octagon etc. may be used according to the aesthetic judgment of a designer. The thin base allows much of the base to slip underneath common items of furniture, such as a bed. See figure 3. If the base is made of a dense metal such as steel, then the weight will be about 7.7 kg. This provides adequate stability for many commonly used tablets. The compact stabilizing weight can provide additional mass for stabilizing the tablet stand. If 105 less weight is needed, then a low density material such as aluminum can be used. If more weight is needed then a higher density material, such as steel can be used. The weight can be made relatively tall and narrow so that the vertical pole can be positioned near the edge of a piece of furniture. A suitable diameter is about 10 cm. A suitable height is about 10 cm. The shape of the weight can be dictated by aesthetic considerations. A circular cylindrical shape is 110 shown in figure 2A. Square, rectangular, octagonal and other shapes are suitable. An ornamental disk 209 may also be placed on top of the weight.

The bent vertical pole 210 can be made of any suitable durable material, such as plastic or metal. Aluminum tubing is suitable. The bent vertical pole is free to rotate in the base about

115 axis 215. The total height of the bent vertical poll 211 can be dictated by the intended use. A total height of about 90 cm is suitable for many household uses, such as lying on a bed or sitting in a chair. The bent vertical pole has an angled section 212 and an upper vertical section 214. Thus the centerline of the T joint at the top of the vertical pole 213 is offset 218 from the centerline of the base 215. A suitable offset is about 15 cm. This offset helps counterbalance

120 the tablet and reduces the need for a counter weight on the boom. It also allows for a relatively long radius of vertical motion 242 and a correspondingly shallow arc of vertical motion 244. A suitable radius of vertical motion is in the range of about 33 to about 44 cm. The radius of vertical motion can be made adjustable by providing a telescoping portion of the boom (not shown). Thus an additional advantage of the offset is that the vertical height of the tablet can be

125 adjusted with minimal side to side motion.

A further additional benefit of the offset is that the arc of horizontal swing 248 is reduced. With an offset of about 15 cm, the radius of horizontal swing 246 can range from about 18 cm to about 29 cm when the boom is in about a horizontal orientation. This gives a small arc of 130 horizontal rotation 248 which allows the tablet to me moved easily out of the way when a user is done with it and wants to, for example, get up out of a chair or bed.

The particular shape of the vertical pole can be dictated by aesthetic considerations as long as the result is a suitable offset with the ability of the pole to rotate about at least approximately the 135 centerline of the base. The cross sectional shape of the vertical pole can also be varied according to aesthetic considerations. A square cross section or flat ribbon, for example, would be functional. The pole may be made of a suitably sturdy material such as aluminum. The diameter of the pole may be one of suitable strength for the given material used. A diameter of about 2.54 cm is suitable for an aluminum pole.

140

The T joint 220 comprises a relatively large diameter friction plate 252. Figure 9 presents an exploded view of the components of a smoothly adjustable tablet stand, including the components of the T joint shown in figure 2A. Referring to figure 9, the T joint comprises a central friction plate 902 held between two outer friction plates 904. Only one of the two outer

145 friction plates is visible in Figure 9. Lubrication means 906 are placed between the center friction plate and the outer friction plates. Suitable lubrication means includes Teflon® discs. These lubrication means are suitable for most metal friction plates including aluminum. Aluminum is a suitable material for the friction plates. .635 cm is a suitable thickness for the friction plates. Alternative suitable lubrication means include sheets comprising a fluorinated

150 polymer, graphite disks and fluid lubricants, such as oil or grease. Clamping means, such as Sex bolts 908, are provided to provide pressure forcing the outer friction plates towards the center friction plate. It has been surprisingly discovered that by providing lubrication between the friction plates, the net stiction will decrease faster than the absolute stiction. This will lead to smoother movement but at the expense of requiring higher clamping force and/or larger

155 frictional surface area that would otherwise be required. In the instant example, the lower absolute stiction caused by the lubrication between the friction plates is compensated for by using large diameter friction plates relative to the frictional surfaces of Springer's T joint. A suitable diameter 252 (Figure 2A) for the friction plates is about 7.5 cm. Diameters as small as 3 cm may be suitable. Suitable clamping pressure can be provided by the Sex bolts discussed

160 above using a wrench for tightening. Once the Sex bolts are set at the appropriate torque, they can be left at said setting. The torque can be adjusted for different weights of tablets. Alternatively, a hand wheel (not shown) can be provided to set or adjust the torque on the Sex bolts. A suitable diameter of the hand wheel is about 6 cm.

165 Referring back to figure 2A, the central friction plate is attached to the horizontal boom by a standoff 254. The standoff should be tall enough so that the boom can be rotated down for storage. The boom does not have to be able to be perfectly vertically oriented. It should be sufficiently vertical, however, such that the distal end of the boom does not extend past the edge of the base 202.

170 The standoff may have an opening 256. The opening should be large enough to allow a charging and/or communications cable and its associated connector terminal to pass there through. This will allow power and/or wired digital communication to be provided to the tablet. See figure 3. The shape of the standoff and associated opening can be dictated by aesthetic 175 considerations. The materials of construction can be any suitable or durable material, such as aluminum or other metal or plastic.

As discussed above, the boom 222 may be telescoping. The counterweight 258 may have significant weight, or may be merely ornamental. It can be eliminated entirely if aesthetic 180 considerations dictate. It is a surprising benefit of the relatively large lubricated friction plates that the T joint can have sufficient absolute stiction such that the tablet height can be adjusted and stay in position without undue net stiction that would lead to jerking of the boom and/or tipping of the stand when the tablet is first put in motion.

185 Details of the back of the spring gripper and associated ball joint are shown in Figure 2B. The boom 262 is attached to the ball joint 264 behind the spring gripper 266. The spring gripper is shown holding a tablet 268. The spring gripper comprises a movable half 272 and a fixed half 274. Each half comprises one or more fingers 276 which reach around 232 (Figure 2A) and hold a tablet. The two halves are urged together by one or more springs 278. One or more slots

190 282 and pins 284 may be provided to guide the motion of the two halves. A thumb tab 286 may be provided on the movable half. This allows a person to squeeze the halves apart by gripping the ball joint and pressing on the thumb tab with the thumb in the same hand. This makes it convenient to insert, remove or adjust the position 288 of the tablet in the spring gripper.

195 As will be discussed in more detail with reference to figure 4, functional considerations for designing the fingers in combination with aesthetic considerations for providing smooth curvature to the back of the spring gripper lead to a bowed shape of the back of the spring gripper and hence a relatively large distance between the center of mass of the tablet and the center of the ball in the ball joint. This can lead to relatively large torque about the center of the

200 ball relative to the Springer design. This torque can be minimized by tilting the tablet slightly relative to the vertical and moving the tablet up or down within the spring gripper so that the center of mass of the tablet is more nearly in vertical alignment with the center of the ball. If the tablet is facing slightly up, for example as illustrated in figure 2B, then the tablet can be moved up on the spring gripper to more closely vertically align the center of mass of the tablet with the 205 ball center. Conversely, if the tablet is angled down, then the tablet can be moved down in the spring gripper.

The spring gripper can be made of suitable durable materials such as aluminum, steel, other metals or plastics. The springs should have a combined force that is readily compressible by a 210 person of ordinary strength. Provision can be made for persons with compromised strength or dexterity, such as those with arthritis. Said provisions can include, for example an enlarged thumb tab, electrically powered gripper, etc.

DESCRIPTION OF THE DRAWINGS

215 Figure 1 A is an exemplary prior art tablet stand.

Figure IB is an exemplary prior art tablet holder.

Figure 2A is an exemplary embodiment of a smoothly adjustable tablet stand.

Figure 2B is an exemplary embodiment of a tablet spring gripper for a smoothly adjustable tablet stand.

220 Figure 3 shows a smoothly adjustable tablet stand in use by a person reclining in bed.

Figure 4 shows a plan view of a magnetic ball joint and spring gripper holding a tablet.

Figure 5 is a detail of an exemplary magnetic ball joint.

Figure 6 is a detail front view of an exemplary tablet spring gripper.

Figure 7 is a detail side view of an exemplary T joint.

225 Figure 8 is a detail perspective view of an exemplary base and compact stabilizing weight.

Figure 9 is an exploded view of an exemplary smoothly adjustable tablet holder.

Figure 10 is a perspective view of the assembled tablet holder of figure 9.

BEST MODE FOR CARRYING OUT THE INVENTION

230

The detailed description presents various embodiments of the invention(s) disclosed herein.

Figure 3 shows an example of the smoothly adjustable tablet stand 300 in use by a person 302 reclining in bed 304. A power cord 306 has been inserted through the opening 307 in the T joint 235 and attached 309 to the tablet 308. Thus the person may enjoy the tablet for an extended period of time. The boom on the stand has a telescoping portion 312 which has been extended so that the tablet is in front of the person. The base 314 fits underneath the bed. Thus the vertical pole 316 can rest next to the bed. If the person needs the tablet to be up higher or down lower for preferred viewing, then the relatively long boom will give a shallow arc of motion and the 240 movement will be nearly vertical. If the person is finished and wishes to leave the bed, the offset of the vertical pole away from the bed will allow the tablet to be pushed away in a relatively tight arc.

Figure 4 shows a plan view of a spring gripper 402 holding a tablet 404. The spring gripper is 245 attached to a ball joint 406 which is attached in turn to a boom 408. Two different tablets are also show separately in cross section to illustrate relative shapes. Tablet 440 is an iPad® by Apple Inc. Tablet 450 is a Kindle® by Amazon.com, Inc.

As described above with reference to figures 2B, a spring gripper comprises a fixed half 412 and 250 a moveable half 414. Both halves can be made moveable relative to the ball joint if desired.

The two halves are joined by at least one spring 416 which urges them together. At least one slot (282 figure 2B) and corresponding pin 418 are provided to guide the motion of the two halves relative to each other. Each half comprises one or more fingers 422 which reach around the tablet. Each finger may comprise an elastomeric seat 424 to assist in gripping and

255 conforming to the shape of the tablet held therein. The moveable half may comprise a thumb tab 426. By squeezing the thumb tab and ball joint, the two halves and then their respective fingers will be moved apart. This will allow for easy insertion, removal or adjustment of the tablet. The amount of relative motion 428 allowable may be set by the span of a normal person's hand. A range of motion of about 5 cm, for example, is suitable. The spacing 430 of 260 the fingers, therefore, can range over many of the common widths or heights of tablets. If the minimum spacing is about 17 cm, for example, then the maximum can be 21 cm. Table 1 below illustrates that this range of finger spacing is suitable for a variety of commonly used tablets.

Comparison of common Tablet Computers

Table 1

Height Width Depth Weight

Tablet cm cm cm grams

Kindle® Keyboard 3G 19.00 12.30 0.85 247 iPad® mini (Wi-Fi) 20.00 13.47 0.72 308

Kindle® Fire HD 8.9" 24.00 16.40 0.88 567 iPad® 2 (Wi-Fi) 24.12 18.57 0.88 601

iPad® with Retina

display (Wi-Fi &

Cellular) 24.12 18.57 0.94 662 The height or width of a given tablet that falls in the range of 17 to 21 cm for the gripper fingers 265 is shown with a heavy bold border. Larger or smaller grippers can be provided to accommodate larger or smaller classes of tablets. The spring grippers can be easily changed out by virtue of the use of a magnetic ball joint.

The fingers have a depth 432 suitable for the depths of tablets 442, 452 commonly used. A 270 depth of about 2 cm is suitable for iPads and Kindles. The curvature or slope 434 of the back of the fingers should be similar to the curvatures or slopes 444, 454 of the back edges of common tablets. A radius of curvature of about 1 cm or greater is suitable. Alternatively or jointly, a slope of about 45 degrees is suitable. These slopes and curvatures provide enough contact with tablets inserted therein such that said tablets are held securely in all orientations.

275

The magnetic ball joint 406 comprises a ball 462 and socket 464. The ball may be a

magnetizable material, such as iron, steel or magnetic stainless steel. The ball may have a corrosion resistant coating, such as chromium. The socket may comprise a strong magnet, such as a neodymium based magnet. Neodymium based magnetic ball sockets are available from 280 Ningbo Hilan Magnets of China. The ball should have a mirror surface for smooth operation.

The pin 418 attaching the ball to the fixed half of the spring gripper should be long enough so that the gripper can be rotated through 180 degrees. Less rotation may be acceptable in some applications.

285 It has been discovered that placing a thin cloth 466 between the ball and socket, the net stiction is significantly reduced with a minor reduction in absolute stiction. This makes changing the orientation of the tablet smoother. A suitable cloth is microfiber lens polishing cloth. It is expected that other thin cloths or other lubricating materials will be functional as well.

290 The back of the spring gripper is shown with a modest bow 468 in it. This bow is dictated

primarily by aesthetic considerations so that a smooth curve is shown between the cup shaped fingers. It causes the center of the ball to me moved back from the center of mass of the tablet and thus increase the torque about the center of the ball. As indicated above, however, the center of mass of the tablet can be brought in closer vertical alignment with the center of the ball

295 by tilting the gripper slightly and optionally adjusting the height of the tablet within the gripper. Exemplary Ornamental Design Elements

Figures 5, 6, 7 and 8 illustrate various exemplary ornamental design elements of a smoothly adjustable tablet stand. The design elements may be any subset of the total designs illustrated.

300

Figure 5 shows a side view 500 of an exemplary ball joint design. An exemplary and non- limiting design element is the modified conical extension 502.

Figure 6 shows a front view 600 of an exemplary spring gripper design.

305

Figure 7 shows a side view 700 of an exemplary T joint design.

Figure 8 shows a perspective view 800 of an exemplary base design.

310 Details of Construction

Figure 9 shows an exploded view of the parts of an exemplary smoothly adjustable tablet holder. Synonyms for above referenced parts may be used. Correspondence is indicated by similar shape and function. The items illustrated in figure 9 are:

• Furniture Glides 912

315 · Base 914

• B ase Cylinder 916

• Detent Spring Retaining Set-Screw 918

• Vertical Support 920

• Male Sex Bolt 908

320 · Teflon® Washer (2) 906

• U-Part 904

• Female Sex Bolt 909

• D-Part 902

• Teflon® Rod 922

325 · Terminal 924

• Lock Washer 926

• Boom 928

• Lock Washer 930

• Magnetic Ball Joint 932 330 Teflon® Bushing 934

Cradle Bottom 936

Cradle Top 938

Springs (2) 940

Teflon® bushings (2) 942

335 Machine Screws (2) 944

The embodiment illustrated in figure 9 differs at least in part from the embodiment illustrated in figure 2 A by the provision of the Tefion® rod 922. The Teflon rod is attached to the D part 902 and fits in a slot (not shown) cut in the boom 928. The rod fits tightly within said slot. This 340 allows for the position of the boom to be adjusted horizontally. The tightness of fit is sufficient so that the boom stays in place once adjusted. Additional tightening means, such as a set screw or clamp may be provided to help secure the horizontal position of the boom relative to the D part.

Figure 10 shows the embodiment of figure 9 in its assembled condition 1000 and holding tablet.

Alternative Embodiments

Having thus described exemplary embodiment(s) of the present invention(s), it will be

350 understood by those skilled in the art that many changes in construction and circuitry and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the present invention as defined in the claims. The disclosures and the description herein are intended to be illustrative and are not in any sense limiting of the invention. For example, a shorter version of the illustrated inventions may be suitable for table 355 top use. The bottom of the vertical pole may be firmly attached to a surface by, for example a fixed mounting, such as a bolt. A clamp may be provided to attach the vertical pole to the edge of a table. Smaller versions of the grippers may be provided for smart phones, such as an iPhone. Larger versions may be provided for large screen TVs or monitors.

360 It will also be understood by those skilled in the art that each inventive element disclosed herein is independently inventive of the other inventive elements. The inventive element of a ball joint with a cloth disposed between the ball and socket of said ball joint, for example, is independently inventive of the bent vertical rod in combination with the boom. Similarly, the bent vertical rod in combination with the boom is independently inventive of the large diameter 365 T joint, the flat base and the spring gripper. Each of these is also independently inventive of each other.

It will also be understood by a person of ordinary skill that the combinations of the

independently inventive elements disclosed herein are also inventive by virtue of the synergies 370 displayed in the combination. The combination of the large diameter T joint, for example with the bent vertical pole and the boom reveals the synergy of the elimination of the need for a counterweight on the boom.

Claims

375 CLAIMS What is claimed is:

1. A smoothly adjustable tablet stand, said tablet stand comprising:

a. a bent vertical pole;

b. a T joint;

380 c. a boom; and

d. a gripper

wherein the top of said bent vertical pole is offset from the bottom of said bent vertical pole such that the axis of horizontal rotation of said T joint is offset from the axis of horizontal rotation of said bottom of said vertical pole.

385 2. The tablet stand of claim 1 wherein said T joint comprises a first friction plate and a second friction plate and a lubricant disposed therebetween.

3. The tablet stand of claim 2 wherein said lubricant is a sheet comprising a fluorinated polymer.

4. The tablet stand of claim 2 wherein the diameter of said first friction plate is at least 3 390 cm.

5. The tablet stand of claim 1 wherein said gripper is attached to the distal end of said boom by a ball joint and wherein said gripper comprises:

a. a first half: and

b. a second half

395 wherein said first half and said second half each comprise at least one finger for gripping a tablet computer and wherein said first half and said second half are joined by a spring which urges said fingers on each half towards each other.

6. The tablet stand of claim 5 wherein each finger is described by a radius of curvature and wherein said radius of curvature is 1 cm or greater.

400 7. The tablet stand of claim 1 wherein said gripper is attached to the distal end of said boom by a magnetic ball joint and wherein a lubricant is disposed between the ball of said ball joint and the socket of said ball joint.

8. The tablet stand of claim 7 wherein said lubricant comprises a cloth.

9. The tablet stand of claim 1 which further comprises at least one of:

405 a. a flat base;

b. a clamp; and

c. a fixed mounting to a surface.

10. A magnetic ball joint, said magnetic ball joint comprising a magnetizable ball, a magnetic socket and a lubricant disposed therebetween.

410 11. The magnetic ball of claim 10 wherein said lubricant is a cloth.

12. The magnetic ball of claim 10 wherein said lubricant is a micro fiber polishing cloth.

13. A T joint, said T joint comprising a first friction plate, a second friction plate, a lubricant and a means for urging said first friction plate and said second friction plate together wherein said lubricant is disposed between said first friction plate and said second

415 friction plate.

14. The T joint of claim 13 wherein the diameter of said first friction plate and said second friction plate is at least 3 cm and wherein said lubricant comprises a fluorinated polymer.

420

425