JPS6121409A - Reusable anchor bolt assembly - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Background of the Invention] This invention relates to an anchor bolt assembly for securing objects to various surfaces. Currently, anchor bolts are divided into two groups depending on the type of structure into which they are inserted. One group of anchor bolts, the round bolts and the round bolts, are specifically designed for attaching objects to hollow surfaces, such as those commonly found in residential buildings.

These hollow wall anchor bolts include a cylindrical sleeve having a series of circumferentially spaced longitudinal slits. Each sleeve also includes an annular groove that serves as a weak area in the center of the sleeve. After inserting the bolt and sleeve combination lj' into the hollow wall, the bolt is tightened, causing the weak groove area of the sleeve to bend and spread behind the wall. As the sleeve expands outward, the longitudinal slits in the sleeve form a series of petals. After the metal between the slits has expanded outward, when the toggle or molypol 1- is further tightened, the petals abut against the inner surface of the wall. Further tightening creates a clamping force between the object attached to the front part of the wall and the petal formed behind the wall.

Togglepol 1~ and Morivolt have several drawbacks. First, they can only be reused. The toggle bolt also has a sleeve that is permanently attached when the moly bolt is tightened.
or plastically deformed.

Toggle or Morivolt cannot be used again. Second,
The sleeve cannot be removed from the hollow hole without creating a gap hole larger than the hole into which the bolt was originally installed. Furthermore, toggle bolts and harpoon bolts cannot apply uniform force to the inner surface of the wall along the inner circumference. Since there are spaces between the petals of the deformed sleeve, the clamping force is not applied uniformly to the wall surface.

The second group of anchor bolts, namely anchor bolts, lag bolts, and plastic sleeves with re-expansion slits, attach objects to hard surfaces. The lead anchor consists of a cylindrical lead plug with a hole therein. A lead plug is placed on the face of the hole, and a punch is driven into the hole in the plug by striking the opposite side of the punch. The punch deforms the lead plug during insertion and calibrates the lead plug against the inside of the hole in the face.

Lead anchors have several drawbacks, such as shock loading of the hole during installation, limited expansion, inability to reuse the lead anchor, and difficulty in retracting the lead anchor.

The lag bolt consists of a large threaded member with a hexagonal head. Lag bolts are commonly used to attach objects to solid wooden surfaces. Lag bolts (well, they do have some drawbacks, including the possibility of cracking decorative wooden surfaces and the need for large torques to install lag bolts in water).

The expandable slit plastic sleeve consists of a threaded plastic sleeve with a longitudinal slit. When the fastener is placed inside the sleeve,
It acts as a simulant to break the sleeve along the slit, forcing the resulting longitudinal plastic nug piece against the inner surface of the hole. Inflatable sleeves, like 1-Gluvolt and Molypol 1-, also suffer from the disadvantage of not being able to apply uniform pressure to the inner surface of the hole. Inflatable sleeves are also not reusable.

The inherent disadvantage of these two groups of anchor bolts is that they have rather special applications for hollow surfaces or for various solid surfaces. Moly bolts or toggle bolts cannot be used effectively on hard surfaces because the petals do not expand outward. Lag bolts are not effective on hollow surfaces.

Expandable slit sleeves and lead anchors have a small holding force in hollow surfaces because the hole depth is limited by the wall thickness. They are suitable towards solid walls.

Some types of anchors have very specific adaptations, so contractors and hardware stores must have several types of anchor bolts available for different types of adaptations.

SUMMARY OF THE INVENTION There is thus seen a need for a reusable anchor assembly that can be applied to solid or hollow surfaces. Anchor bolts are also needed to provide even pressure around the hole in the face.

The reusable anchor assembly of the present invention cures the above-mentioned drawbacks. The assembly consists of an expansion body and a threaded fastener. The inflatable body has a tubular section made of a resilient material and has an end plate attached to the innermost end of the assembly. The opposite or central end of the expander is constructed with a mating flange to secure the object or workpiece to the surface. The end plate is also threaded to mate with the threaded fastener. The fastener enters the tubular portion of the expander through the object or workpiece and engages the end plate. When the fastener engages the end plate, an axial compressive force is exerted on the tubular section. This compressive force is counteracted by seven lunges acting on the workpiece. The 7-lunge acts as a wide support for compressive forces to prevent slip damage to the workpiece. Finally, when the axial load becomes large enough,
The tubular portion protrudes and bulges outward from the shaft of the fastener.

In use, the assembly is preferably placed in a bore slightly larger than its uncompressed outer diameter. When the tubular part is bent, it acts against the inner surface of the hole in which it is installed. As the axial load increases, the expansion forces acting outwardly against the inner surface of the hole also increase.

The resilient material of the tubular portion of the anchor assembly also has a high coefficient of friction, creating a force that resists withdrawal of the anchor assembly from the hole. The material used to construct the tubular portion of the anchor assembly is resilient and therefore returns to its original shape when the axial force is removed. As a result, this anchor assembly can be reused.

In one embodiment, the flange is integral to the elastic inflatable body and becomes part of the formwork into which the inflatable body is injection molded. In this embodiment, the end plate is a rigid, inelastic, metal member that is preferably placed in the mold prior to injection of the elastomeric polymeric material from which the inflatable body is manufactured.

In a second embodiment, the flange and end plate are each manufactured separately from the inelastic expansion body. Thereafter, they are press-fitted into a pair of fitting portions formed at each end of the inflatable body. This embodiment has the advantage of providing additional support to the fastener and sealing the path for cold outflow of the expander material. This advantage maintains long-term holding pressure of the assembly. In this embodiment, the manufacture of the inflatable body is also facilitated since there is no need to manually place the end plates in the mold, increasing productivity.

DESCRIPTION OF THE EMBODIMENTS Referring to FIG. 1, the reusable anchor assembly can be used to attach a workpiece 36 or other object to a work piece 38. The reusable anchor assembly is disposed through the workpiece 36 and into the hole 40 in the surface 38. The surface 38 or substrate may be a wall, ceiling, floor, etc., and may be hollow, such as a sheetrock wall, or the surface may be solid, such as a concrete wall. good. The reusable anchor assembly consists of a threaded fastener 12 and an expansion body 14. The inflatable body 14 is comprised of a threaded nut-like end plate 16 and a tubular section 30.

Fastener 12 is, in the preferred embodiment, a conventional wood or sheet metal screw having a threaded shank 18 and an enlarged head 20. It should be understood that machine screws or any other type of screw can be used as the fastener.

1 and 2, end plate 16 is attached to tubular body 30 by molding, gluing, or other suitable means.
The tubular portion 30 and the end plate 16 cooperate with each other. The end plate 16 is comprised of a pair of coaxial cylinders consisting of a large cylinder 24 attached to a small cylinder 26. The difference in the outer diameters of cylinders 24 and 26 forms a shelf 34. A cylindrical hole 28 passes through the common axis of both cylinders 24 and 26. The inner surface of this hole 28 is threaded to threadably engage the shank 18 of the fastener 12. The small cylinder 26 is knurled on its outer peripheral surface as shown at 27. Although the end plate 16 in the preferred embodiment is comprised of two cylinders, it is understood that many shapes and sizes may result in a suitably functioning end plate.

Referring again to FIGS. 1 and 2, the tubular portion 30 of the inflatable body 14 is sleeve-shaped and has a flange 32. As shown in FIGS. In this embodiment, the flange 32 is integral with the tubular portion 30 of the inflatable body 14 and is injection molded of a resilient polymeric material. It goes without saying that other materials and manufacturing processes can also be used. As can be seen from the drawing, the outer end surface 33 of the 7 flange contacts the workpiece 36,
Inner end surface 35 contacts hole 38 surrounding hole 40 . The inner end surface 35 of the flange 32 provides an anchor for the assembly to prevent the seven langes from completely entering the bore 40 and disappearing from view, and provides a surface on which axial compressive forces are applied, as will be discussed in more detail below. The outer end surface 33 of the seven flange 32 provides a base or support surface on which the object 36 is mounted so that it does not slip or cause damage to the workpiece.

The tubular portion 30 of the expansion body 14 is connected to the threaded shaft portion 18 of the fastener 12.
It has an inner diameter slightly larger than the outer diameter. Tubular part 30
The walls are relatively thin so that they deflect when a force is applied to their ends, thereby creating an axial compressive force on the tubular portion 30. The thickness of flange 32 is approximately half the thickness of the wall of tubular body 30.

The tubular portion 30 is a small cylinder 26 equipped with knurls.
completely molded around. The peripheral knurled surface of the small cylinder 26 provides a gripping force between the tubular section 30 and the end plate 16 to form a permanent bond therebetween. It will be appreciated by those skilled in the art that other shapes can be connected directly to the ends of the tubular portions 30 of the end plates to form an inflatable body 14 that functions similarly to the preferred embodiment described above.

For example, end plate 16 can be formed as a cylinder having a diameter smaller than the outer diameter of tubular section 30 in its unforced or released state. It is then possible to mold the tubular portion 30 over the entire outer circumferential surface of the end plate. The length of the dilatator 14 is less than the length of the shank 18 of the fastener 12 by the thickness of the workpiece 36, thereby ensuring engagement between the dilatator and the fastener.

The tubular body 30 of the inflatable body 14 is made of an elastic material with a high elastic limit. When the force that causes the material to deform is released, the deformation also disappears.

In other words, under typical circumstances, the set to the deformed state will not remain in the tubular portion 30 of the expandable body 14, but rather will return to its original shape after the large deforming force is released. Typical environments also include using the reusable anchor assembly near sources of heat generation or exposing the reusable anchor assembly to sunlight for a period of time or more. Even after use in a non-typical environment, upon relaxing the deformation force, the expander will eventually relax to the point where the diameter of the loosened tubular portion 30 is less than the diameter of the hole 40.

The material of the tubular portion 30 of the inflatable body 14 is relatively compression-resistant;
and has a high coefficient of friction.

Thus, as the load on the material increases, the force required to move the material along a plane perpendicular to the line of action of the force also increases. Additionally, it is desired that the materials used also have relatively low critical buckling load characteristics, such that the thin walls of the expandable body 14 bend or protrude outwardly at low compressive forces due to the low critical buckling load characteristics. The material used in the preferred embodiment is polyurethane, although vinyl, rubber, or other similar materials are also suitable. If polyurethane, vinyl, rubber, or similar materials are used, the anchor also electrically isolates the workpiece 36 from the workpiece 38.

Fasteners 12 and end plates 16 are formed of metal in the preferred embodiment described above. However, great strength,
And other materials having reduced deformation properties when compared under similar loads to the material of tubular portion 30 can also be used.

In operation, the dilatator 14 is disposed within the hole 40 in the mounting surface 38 and the hole 44 in the workpiece 36 is aligned with the hole 42 in the dilatator 14 . Then the fastener 12 is inserted into both holes 42.4.
4 and inserted into the tubular section 30 or end plate 16. Separately, the fastener 12 is inserted through the hole 44 of the workpiece 36 and the expansion body 14, and then
The tubular portion 30 of the inflatable body and the end plate 16 may be placed within the hole 40 with the tube 6 attached thereto.

The fasteners 12 may be rotated into engagement with the end plates 16 to complete the attachment. The fastener can be rotated with a regular forceps until the length of the shaft 18 between the end plate 16 and the head 20 of the fastener 12 is equal to the thickness of the workpiece 36 and the length of the dilatator 14. screwdriver,
A spanner or other suitable means of turning the fastener or applying 1-lux is necessary to complete the installation.

Applying torque to fastener 12 causes shaft 18 to thread into end plates 1-16, thereby drawing end plate 16 toward workpiece 36. The reverse movement of the expander 14 causes the inner surface 35 of the 7 flange 32 to
This is prevented by engaging the surface 38 surrounding 0.

This creates an axial compressive force in the tubular section 30.

When the fastener is further tightened, the tubular portion 30 of the expander
The axial compressive force of increases up to the critical buckling load. The force exceeds the critical buckling load.

Then, the wall of the tubular portion 30 is virtual @! in FIG. It projects outwardly, as shown at 46, away from the axis 18 of the fastener 12. The phantom line 46 shows only one protruding position of the tubular portion 30. The wall bending protrudes further outward as the axial compressive force increases until the wall of the tubular portion 30 contacts the inside of the wall 40 of the mounting surface 38. After contact, further tightening of the reusable anchor assembly creates an expansion force acting radially outwardly on the inner surface of the hole 40. The wall of the tubular portion 30 or sleeve projects around the shaft 18 and is in constant contact with the inner surface of the bore 40 and applies uniform pressure thereto. Constant contact around the hole 40 seals the hole 40 and prevents fluid flow.

Upon examination, it can be seen that the reusable anchor assembly engages the hole 40 of the tubular portion 30 after the tubular portion 30 undergoes two movements. Two movements occur when the fastener is selectively threaded into the end plate 16. The first movement is flange 3
2 hits the head 20 of the fastener 12 and then the fastener is further screwed together. Further threading tightens the inflatable body longitudinally or more precisely creates an axial compressive force within the tubular portion 30 of the inflatable body 14 .

As the reusable anchor is further tightened, the axial compressive force within the tubular section 30 increases and a second action occurs in which the tubular section 30 bends outwardly and expands. Further tightening causes the wall to bulge or expand further outwardly into contact with the inner surface or interior of the hole 40.

This dual action is advantageous in that the inner surface of the hole 40 experiences only radial forces. This makes installation even easier. The torque required to install this reusable reed force is less than that required for other devices. Many other Ashikab vises □ act as wedges and as a result must be placed against the internal surface along the longitudinal axis of the hole (overcoming frictional forces). This is much easier than overcoming frictional forces.

After the device, the only force contacting the inner surface of the hole 40 extends outward and is perpendicular to its inner surface. Other devices that utilize stroke action not only provide a radial force, but also an axial and parallel force along the inner surface of the hole 4'O.

Furthermore, while the inflatable body 1 is inserted into the hole 40 of the
It will be appreciated that 4 remains compressed.

This is different from the reeding force of the prior art in which there is only a temporary compressive force that disappears immediately when the weakly reeded part is no longer able to form a petal, as described above. Additionally, the anchor assembly of the present invention provides a secure fit for the workpiece 36 against the surface 38 even if the hole 40 widens for any reason.
is effective in supporting In order to increase the compressive force in the tubular part 30 under such circumstances, one can simply turn the snapper 12, thereby fixing the expansion body 14 in the hole 40. Large hole 40 in prior art anchor
In this case, another reed force must be installed, and it is necessary to use thick and thick anchors.

The force applied to the inner surface of hole 40 is uniform. Expanding body 14
Surface contact always exists on the inner surface of the bore 38 when the tubular portion 30 of the tube 30 is bulged outwardly. Preferably, the difference between the outer diameter of tubular portion 30 and the inner diameter of bore 40 is minimized so that the anchor assembly can more effectively retain workpiece 36.

The resistance to withdrawal of the anchor bolt from the hole is directly related to the coefficient of friction of the material of the tubular section 30 and the magnitude of the expansion force acting on the inner surface of the hole 40. As the expansion force increases, the frictional force resisting retraction of the reusable reed force member also increases.

The anchor assembly of the disclosed invention can be used to attach most workpieces 36 to holes 40 and 38. The hole 40 is inserted into the tubular section 3 in a relaxed or unpressurized state for most effective operation.
It has an inner diameter slightly larger than the diameter of 0. The outer diameter of the anchor assembly to which no pressure is applied is the inner diameter of the hole 40'
, the anchor assembly can be inserted with substantially no frictional resistance. However, the difference in diameter should be small enough so that the outer wall of the tubular portion 30 only needs to bulge outward slightly before contacting the inner surface of the hole 40. Due to the small size of the anchor assembly, the difference between the inside diameter of the hole 4o and the outside diameter of the tubular portion 30 can be made to be 1/16 inches and still effectively secure the workpiece. However, the reusable anchor assembly expands to secure the workpiece 36 in the larger diameter hole 40. For example, a 0.25 inch reusable anchor assembly can be placed in a 0.4 inch hole and expanded to adequately hold a workpiece.

As long as the wall pressure and length ratio of the tubular element is maintained properly,
An expander having an outer diameter equal to at least 65% of the inner diameter of the hole 40 can retain the workpiece 36 after installation. However, in order to be most effective, the diameter of the tubular portion 30 of the reusable anchor member is preferably less than (80%) the inner diameter of the hole 40 in the surface 38.

Actual test 1- used a 1/2 inch expansion body in conjunction with the M4 sheet metal screw in the anchor assembly. This assembly withstood over 400 pounds of tip load in destructive testing. This anchor assembly was tested on a 1/2 inch thick section of sheetrock and was found to withstand up to 140 pounds. Of course, large inflatable bodies can withstand thousands of pounds when fixed in a rigid substrate. Additionally, the tensile strength of hole 40 generally exceeds the torque rate of the fasteners used in the anchor assembly.

Very little torque is required to directly install the anchor assembly.

The anchor assembly is also effective in holding the workpiece 36 within the hollow surface 38. A hollow surface is one in which the length of the shaft portion 18 of the fastener 12 is greater than the thickness of the mounting surface 38. In fact, the anchor assembly of the present invention can be used with any fixation to hold virtually any surface of any material of any thickness. Additionally, the inflatable body 14 can be used as a leak-tight seal in ships and other fluid environments, and as an electrical isolation device.

Furthermore, when the expander is used as a fixed member of a motor or engine, it can attenuate any type of imaging.

As mentioned above, the anchor bolt is made of elastic material and can be reused. Thus, when the fastener is loosened and the axial compressive force is released, the tubular portion 30 of the expandable body 14 returns to its original shape. Generally the axial compressive force is applied to the tubular section 3
No permanent or plastic deformation occurs by applying zero. The material of the tubular portion 30 of the inflation body 14 is also elastic. Therefore, the axial load is
When the load is removed, the tubular part returns to its original shape.

It should also be noted that other shapes and sizes of fasteners 12 can be used in various applications using the disclosed invention. Furthermore, the tubular portion 30 of the inflation body 14 can be made large or small depending on the application or use of the reusable Ankapol I.

3 and 4 illustrate another embodiment of the reusable anchor assembly of the present invention, in which the dilatator 48 is constructed from three separately manufactured members. The tubular portion 50 includes
A pair of truncated conical fitting portions 52 are provided at each end thereof, and the ends have a concave circumferential retaining ring 54 sandwiched between the fitting portions 52 and the tubular portion 50. have End plate 56 is made of a non-resilient, preferably metallic material and has threaded holes 58 for receiving fasteners 12, shown in cross-section in FIG. The inside of the end plate 56 is hollowed out to form a frustoconical shape that matches the shape of the fitting portion 52a, and is provided with an annular edge 62 shown in FIG. The end plate 56 is a pressure fit on the distal end of the inflatable body 48 and is pressed against the fitting portion 52a such that the annular edge 62 locks onto the retaining ring 54a to securely hold the end plate 56 in place. Fit together. The elasticity of the fitting portion 52a deforms when the end plate 56 is pressed into contact with the fitting portion, thereby facilitating assembly of the end plate 56.

Flange 64 is assembled to the opposite or central end of inflation body 48 in the same manner as described for end plate 56. The inside of the flange 64 is also hollowed out in the shape of a truncated cone to match the fitting part 52b and is provided with an annular edge 66 (shown in FIG. 4) which cooperates with the retaining ring 54b of the fitting part 521). Thus, the end plate 56 and the flange 6
4 are easily assembled on opposite ends of the inflation body 48.

This embodiment has the advantage of eliminating the need for the end plate to be placed in a mold for injection molding of the inflation body, thereby increasing production efficiency of the inflation body portion of the reusable anchor assembly.

The inner surface 68 of the flange 64 mates with the surface 38 to which the workpiece is mounted. This mounting surface 38 is represented by dashed lines in FIG. This inner surface 68 provides support or a base for the anchor assembly in hole 40 (shown in FIG. 1);
A compressive force acts on the assembly to prevent the IC from entering the hole. The outer surface 70 of the 7 flange 64 engages the workpiece 36. Flange 64 is also preferably made of a non-resilient or metallic material.

The flange 64 is provided with a cylindrical portion 72 having a length sufficient to fit into the hole 40 and an outer diameter approximately the same as the inner diameter of the hole.

Thus, the seven flange 64 with the cylindrical portion 72 completely seals the hole when the fastener 12 is positioned as shown in FIG. 4, preventing any cold escape of the elastic expandable body 48.

That is, because the expandable body is made from an amorphous solid such as a polymer, it tends to flow over time. This glassy state, caused by the low crystallinity of the inflatable body material, will deform the inflatable body if not prevented by the flange. , similarly,
The end plate seals the opposite side of the hole against the compressive force of the expansion and any spillage of the expansion body which would reduce its retention force.

The use and operation of the reusable anchor assembly of FIGS. 3 and 4 is substantially the same as the embodiment of FIGS. 1 and 2. The fasteners 12 extend through the expansion body 48 and into the end plate 5.
It meshes with 6. Then, as the fastener 12 advances, compressive force is applied to the expansion body 48, creating a virtual! Inflate the inflatable body outward as shown at 48-. Inelastic end plate 5
6 and flange 64 provides support for fastener 12 and expansion body 48.
prevent any deflection or deformation of the

The invention may be embodied in other specific forms without departing from its spirit or essential characteristics.

The embodiments described are in all respects illustrative only and should not be considered as limiting. The scope of the invention is, therefore, indicated by the claims rather than by the foregoing description. All changes that come within the meaning and range of equivalence of the claims shall belong within their technical scope.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view of a first embodiment reusable anchor bolt assembly illustrating the resilient flange integral with the expansion body. FIG. 2 is a cross-sectional view of the inflatable body taken along line 2--2 of FIG. FIG. 3 is an exploded perspective view of a second embodiment reusable anchor bolt assembly illustrating the non-resilient end plate and seven langes. FIG. 4 is a cross-sectional view of the second embodiment of the inflatable body illustrating the fully assembled anchor assembly. In the figure, 12 is a fastener, 14 and 48 are expansion bodies, 1
6 and 56 are end plates, 18 is a shaft, 20 is a head, 3
0 and 50 are tubular parts, 32 and 64 are seven flange, 36 is a workpiece, 38 is a surface, 40 is a hole, 52 is a fitting part, 54 is a retaining ring, and 62 is an annular edge. Engraving of drawings (no change in content) I = Mo 7.2 Procedural amendment (method) July 9, 1985

Claims (13)

[Claims] (1) A device adapted to be inserted into a preformed hole (40) in a surface (38) for fixing an object to said surface, the device being capable of being attached to said object and being able to fit into said hole. an expandable elastic element (14, 48) insertable; and an axially compressive force on said element, thereby biasing said element to a substantially radial force acting on an inner surface of said hole. a mechanism (12, 16) for preventing dislodgement of the element from the surface, thereby securing the object to the surface;
) and a device characterized by. 2. The device of claim 1, wherein the mechanism for generating the axial force expands the element radially outwardly into engagement with the inner surface of the hole. (3) The mechanism that generates the axial compressive force further comprises:
an adjustment member (12) and a cooperating member for said adjustment member (
16, 56), wherein the adjustment member and the cooperating member are selectively (i) biased toward each other to impart the compressive force to the element, or (ii) removed from the element. Claims characterized in that it is released in order to release the compressive force, thereby allowing the element to return to its released state and to allow the element to be withdrawn from the hole. Apparatus according to paragraph 1. 4. Device according to claim 1, characterized in that the elasticity of the element makes the device reusable. 5. The device of claim 1, wherein the element is made of a material with a high coefficient of friction to maintain the position of the element in the hole. (6) the adjustment member is a threaded fastener;
4. The device of claim 3, wherein said cooperating means is an end portion threaded onto said fastener, and said element is a sleeve mounted over said fastener. 7. The device of claim 1, wherein expansion of the element forms a seal in the hole that prevents water or other fluids from escaping. 8. The apparatus of claim 1, wherein expansion of the element provides electrical isolation between the object and the surface. (9) Claim 1 further characterized in that it is further characterized by a restriction body attached to said element for maintaining said radial force exerted by said element on said hole. Equipment described in Section. 10. The device of claim 9, wherein the restrictor is characterized by a mechanism that maintains the expanded shape of the element within the hole and prevents deformation of the element over time. (11) The restriction body is constituted by an inelastic means that seals the hole to prevent cold outflow of the elastic element.
Apparatus according to claim 9. (12) A method for attaching an object (36) to a hole (40), comprising: disposing a sleeve (14, 48) of elastic material in the hole; attaching the object to the sleeve; A method comprising applying a compressive force to the sleeve to bias the sleeve outwardly against an interior wall and deform the sleeve to securely secure the object in the hole. 13. The method of claim 12, further comprising the step of sealing the holes to prevent deformation of the elastic material and maintain its compressive force.