Technical Field
[0001] The present invention relates to a brake release mechanism for a hoisting-machine
brake for an elevator.
Background Art
[0002] A brake for stopping a car is provided to a hoisting machine of an elevator. An electromagnetic
coil is provided to the brake. During a normal operation in which the car is raised
and lowered, the electromagnetic coil is energized. By an electromagnetic function,
the hoisting-machine brake is placed in a released state. On the other hand, in case
of emergency such as a power outage or an earthquake, the hoisting-machine brake is
configured so that the energization is interrupted to automatically place the brake
in a braking state. Therefore, as an operation after the car makes an emergency stop,
the hoisting-machine brake is manually released to place the car in a state in which
the car can be raised and lowered and then the car is moved to the nearest floor.
[0003] As a structure for manually releasing the hoisting-machine brake in the situation
described above, there is a structure disclosed in Patent Literature 1. In this structure,
a pin passes through a movable iron core constituting the brake. A distal end of the
pin is screwed into a fixed iron core having an electromagnetic magnet. A head of
the pin projects from a surface of the movable iron core, which is on the side opposite
to the fixed iron core. When the brake is to be released, a wedge-like portion of
a brake releaser is inserted between the head of the pin and the movable iron core.
Through movement of the movable iron core toward the fixed iron core, a brake shoe
supported by the movable iron core is separated from a braking surface of a rotor.
[0004] In a mode in which the brake is released by using the effects provided by the wedge
as described above, however, the brake releaser is subjected to a large frictional
force due to surface contact on the wedge-like portion over a wide area when the wedge-like
portion is inserted between the head of the pin and the movable iron core. Therefore,
enormous effort has been required for a brake releasing operation.
Citation List
Patent Literature
Summary of Invention
Technical Problem
[0006] The present invention has been made in view of the problem described above, and therefore
has an object to provide a brake release mechanism capable of reducing effort required
for a manual brake releasing operation.
Solution to Problem
[0007] In order to achieve the above-mentioned object, according to the present invention,
there is provided a brake release mechanism for a hoisting-machine brake for an elevator,
the hoisting-machine brake including movable bodies for supporting brake shoes and
a fixed base having electromagnetic coils for driving the movable bodies, the brake
release mechanism including: a first member and a second member provided so as to
be rotatable relative to each other; and a plurality of rolling bodies provided between
the first member and the second member, in which: the brake release mechanism further
includes: a plurality of supporting holes for partially housing the plurality of rolling
bodies therein, the plurality of supporting holes being formed on one of a pair of
surfaces of the first member and the second member, which face each other; and a plurality
of elongated holes each extending in an arc-like manner so as to enable a corresponding
one of the plurality of rolling bodies to move while rolling, the plurality of elongated
holes being formed on another of the pair of surfaces ; the plurality of supporting
holes respectively support the plurality of rolling bodies so as to enable the plurality
of rolling bodies to spin by themselves and to move in synchronization with the plurality
of supporting holes; each of the plurality of elongated holes is formed so that a
depth for housing the corresponding one of the plurality of rolling bodies changes
when the plurality of rolling bodies move along the plurality of elongated holes;
each of the plurality of rolling bodies is housed in both a corresponding one of the
plurality of supporting holes and a corresponding one of the plurality of elongated
holes between the first member and the second member so that a distance between the
first member and the second member in a direction of a relative rotation axis changes
in accordance with the relative rotation of the first member and the second member;
the brake release mechanism further includes a securing portion which avoids securing
a position of one of the first member and the second member in the direction of the
relative rotation axis and secures a position of another of the first member and the
second member in the direction of the relative rotation axis; the securing portion
is fixed to the fixed base; and the one of the first member and the second member
is provided so as to apply a traveling force in the direction of the relative rotation
axis to a corresponding one of the movable bodies.
Advantageous Effects of Invention
[0008] According to the brake release mechanism of the present invention, it is possible
to reduce effort required for a manual brake releasing operation.
Brief Description of Drawings
[0009]
[FIG. 1] A schematic view for illustrating an internal-expanding drum brake for an
elevator hoisting-machine, which uses a brake release mechanism according to an embodiment
of the present invention.
[FIG. 2] A view for illustrating a state in which a movable lever and a fixed lever,
which constitute the brake release mechanism, are combined.
[FIG. 3] A view for illustrating a state as viewed from the arrow III in FIG. 2.
[FIG. 4] A sectional view taken along the line IV-IV in FIG. 3.
[FIG. 5] A plan view of the movable lever.
[FIG. 6] A sectional view taken along the line VI-VI in FIG. 5.
[FIG. 7] A plan view of the fixed lever.
[FIG. 8] A sectional view taken along the line VIII-VIII in FIG. 7, for illustrating
an arc-like region extending along the line VIII-VIII which is developed in a planar
form.
[FIG. 9] A view for illustrating the vicinity of one of collars in an enlarged manner
in association with FIG. 2.
[FIG. 10] A view in the same mode as FIG. 1, for illustrating a state in which the
brake release mechanism is assembled to a hoisting-machine brake.
[FIG. 11] A sectional view taken along the line XI-XI in FIG. 10.
[FIG. 12] A view for illustrating a plane taken along the line XII-XII in FIG. 10.
Description of Embodiment
[0010] Hereinafter, a brake release mechanism according to an embodiment of the present
invention is described referring to the accompanying drawings. In the figures, the
same reference symbols represent the same or corresponding parts.
[0011] FIG. 1 is a schematic view of an internal-expanding drum brake for an elevator hoisting-machine,
which uses the brake release mechanism according to this embodiment. A hoisting-machine
brake 1 includes a pair of movable bodies 3 and a fixed base 5.
[0012] The pair of movable bodies 3 are respectively provided on both sides of the fixed
base 5 so as to sandwich the fixed base 5 therebetween. A projection 3a, to which
a fixed lever described below is locked by hooking, is formed on each of the movable
bodies 3. On the side of each of the movable bodies 3, which is opposite to the fixed
base 5, a brake shoe 9 is provided so as to face an inner circumferential surface
of a rotor 7. The brake shoes 9 are respectively supported by the corresponding movable
bodies 3. An elastic body 11 is provided between each of the movable bodies 3 and
the fixed base 5. In this manner, the pair of movable bodies 3 and the pair of brake
shoes 9 are constantly biased toward the rotor 7 by elastic forces of the corresponding
elastic bodies 11, respectively.
[0013] The fixed base 5 includes electromagnetic coils (not shown) in the vicinity of the
pair of movable bodies 3. The pair of movable bodies 3 are driven by the electromagnetic
coils. Specifically, when the electromagnetic coils are energized, the pair of movable
bodies 3 are subjected to driving forces for attracting the movable bodies toward
the fixed base 5 by electromagnetic forces thereof.
[0014] Next, the brake release mechanism according to this embodiment is described. FIG.
2 is a view for illustrating a state in which a movable lever and a fixed lever, which
constitute the brake release mechanism, are combined. FIG. 3 is a view for illustrating
a state as viewed from the arrow III in FIG. 2. FIG. 4 is a sectional view taken along
the line IV-IV in FIG. 3. First, the brake release mechanism includes a movable lever
(first member) 13, a fixed lever (second member) 15, and a plurality of rolling bodies
17.
[0015] The movable lever 13 and the fixed lever 15 are provided so as to be rotatable relative
to each other. The plurality of (three in this embodiment) rolling bodies 17 are provided
between the movable lever 13 and the fixed lever 15, and are formed as, for example,
spherical bodies made of a bearing steel material in this embodiment. The same number
of (three in this embodiment) supporting holes 19 as that of the rolling bodies are
formed on one surface 13a of a pair of surfaces 13a and 15a of the movable lever 13
and the fixed lever 15, which face each other. The same number of (three in this embodiment)
elongated holes 21 as that of the rolling bodies are formed on the another surface
15a. The supporting holes and the elongated holes are further described referring
to other figures.
[0016] FIG. 5 is a plan view of the movable lever. FIG. 6 is a sectional view taken along
the line VI-VI in FIG. 5. FIG. 7 is a plan view of the fixed lever. FIG. 8 is a sectional
view taken along the line VIII-VIII in FIG. 7, for illustrating an arc-like region
extending along the line VIII-VIII, which is developed in a planar form.
[0017] First, as illustrated in FIG. 5, the movable lever 13 includes a body portion 23
and a lever-piece portion 25. The body portion 23 is a circular disc-like portion
provided about a rotation axis CL for the above-mentioned relative rotation. In a
central portion of the body portion 23, a through hole 27 is formed. The lever-piece
portion 25 is a portion extending in a radial direction for the relative rotation,
and specifically, is a portion extending from the body portion 23 outward in a radial
direction of the body portion 23 in this embodiment.
[0018] Each of the supporting holes 19 is a recess which is open on the above-mentioned
one surface 13a of the body portion 23. Each of the supporting holes 19 has a form
in which each of the rolling bodies 17 is partially housed, and for example, has a
shape in accordance with an outer shape of each of the rolling bodies 17 (inner-surface
shape similar to the outer shape of each of the rolling bodies). Specifically, each
of the rolling bodies 17 is a spherical body in this embodiment, and hence the inner-surface
shape of each of the supporting holes 19 is formed as a spherical surface shape. Moreover,
a depth of each of the supporting holes 19 is a half of a diameter "d" of the spherical
body forming each of the rolling bodies 17, as illustrated in FIG. 6, that is, d/2.
As described above, in this embodiment, each of the supporting holes 19 is a semi-spherical
recess. Because of the form of each of the supporting holes 19 described above, each
of the supporting holes 19 supports a corresponding one of the rolling bodies 17 in
a mode in which the rolling body cannot move in the hole but can spin by itself in
the hole, in other words, in a mode in which the rolling body can move and spin by
itself in synchronization with a corresponding one of the supporting holes.
[0019] The three supporting holes 19 are arranged on a circumference having a single radius
about the center (relative rotation axis CL) of the body portion 23 in plan view.
Further, each of the supporting holes 19 is separated from another adjacent one of
the supporting holes 19 at an equiangular distance (120 degrees in this embodiment)
in plan view.
[0020] On the other hand, as illustrated in FIG. 7, the fixed lever 15 includes a body portion
29 and a fixing-arm portion 31. The body portion 29 is a circular disc-like portion
provided about the relative rotation axis CL. A through hole 33 is formed in a central
portion of the body portion 29.
[0021] The fixing-arm portion 31 is a portion relating to the relative rotation, which extends
in the radial direction, and specifically, is a portion extending outward in the radial
direction of the body portion 29 from the body portion 29 in this embodiment. In the
vicinity of a distal end of the fixing-arm portion 31, a pair of hooks 35 are provided.
The pair of hooks 35 are a pair of protruding portions vertically standing on a surface
opposite to the above-mentioned another surface 1.5a, on which the elongated holes
21 are formed, specifically, a surface on the side which faces a corresponding one
of the movable bodies 3 at the time of completion of assembly. Then, when the brake
is to be manually released, the above-mentioned projection 3a of the corresponding
one of the movable bodies 3 is inserted between the pair of hooks 35.
[0022] Each of the elongated holes 21 is a recess which is open on the above-mentioned another
surface 15a of the body portion 29. The elongated holes 21 have a form for partially
housing the rolling bodies 17 therein and are arranged about the relative rotation
axis CL, each extending in an arc-like shape. Further, as illustrated in FIG. 7, each
of the elongated holes 21 has a shape which corresponds to a locus obtained when a
circle is moved in an arc-like manner in plan view. An inner-surface shape of each
of the elongated holes 21 corresponds to an outer shape of each of the rolling bodies
17, and specifically, is a shape which corresponds to a locus obtained when a spherical
surface is moved in an arc-like manner in this embodiment, as illustrated in FIG.
8. A depth of each of the elongated holes 21 changes in accordance with the position
in a direction in which each of the elongated holes 21 extends in the arc-like manner,
as illustrated in FIG. 8. Specifically, each of the elongated holes 21 is formed so
that a depth for housing a corresponding one of the rolling bodies 17 therein changes
when the rolling body 17 moves along the elongated hole 21. In this embodiment, the
relationship between a maximum depth Xmax of each of the elongated holes 21 and a
minimum depth Xmin thereof which changes approximately linearly from the maximum depth
is:
with respect to the diameter "d" of each of the rolling bodies 17. With such a form
of each of the elongated holes 21, each of the rolling bodies 17 can move along a
direction in which the elongated holes 21 extend while rolling inside a corresponding
one of the elongated holes 21. Moreover, the depth for housing each of the rolling
bodies 17 (in other words, a height of a part of each of the rolling bodies 17, which
is exposed from a corresponding one of the elongated holes 21) changes in accordance
with the movement of the rolling bodies 17.
[0023] The three elongated holes 21 are arranged on a circumference having a single radius
about the center (relative rotation axis CL) of the body portion 29 in plan view.
Further, each of the elongated holes 21 is separated from another adjacent one of
the elongated holes 21 at an equiangular distance (approximately 120 degrees between
the centers of the elongated holes in the circumferential direction in this embodiment)
in plan view.
[0024] Each of the rolling bodies 17 is partially housed in a corresponding one of the supporting
holes 19 having the configuration described above on one side, and is partially housed
in a corresponding one of the elongated holes 21 having the configuration described
above on the other side. Specifically, each of the rolling bodies 17 is housed in
both a corresponding one of the supporting holes 19 and a corresponding one of the
elongated holes 21 between the movable bodies 3 and the fixed base 5. As a result,
a distance between each of the movable bodies 3 and the fixed base 5 in the direction
of the relative rotation axis CL varies in accordance with a rotating operation of
the movable bodies 3 and the fixed base 5 relative to each other, specifically, in
accordance with the positions of the rolling bodies 17 in the elongated holes 21.
[0025] The brake release mechanism according to this embodiment further includes a cover
member and a plurality of collars. The cover member and the plurality of collars are
described referring to FIGS. 2 and 9. FIG. 9 is a view for illustrating the vicinity
of one of the collars in an enlarged manner in association with FIG. 2. As illustrated
in FIGS. 2 and 9, a cover member 37 is provided so that the movable lever 13 is interposed
between the cover member 37 and the fixed lever 15. Each of collars 39 is a cylindrical
member and is provided between the cover member 37 and the fixed lever 15 so as to
maintain a distance between the cover member 37 and the fixed lever 15. Through a
hollow portion of each of the collars 39, a collar screw 41 is inserted. By the collar
screws 41, the cover member 37 and the fixed lever 15 are connected to each other.
[0026] The brake release mechanism further includes a securing portion. For example, the
securing portion does not secure the position of one of the movable lever 13 and the
fixed lever 15 in the direction of the relative rotation axis CL but secures the position
of another thereof in the direction of the relative rotation axis CL. In this embodiment,
the securing portion is formed of a release bolt fixed to the fixed base 5. The securing
portion is described referring to FIGS. 10 and 11.
[0027] FIG. 10 is a view in the same mode as that of FIG. 1, for illustrating a state in
which the brake release mechanism is assembled to the hoisting-machine brake. FIG.
11 is a sectional view taken along the line XI-XI in FIG. 10. As is most clearly illustrated
in FIG. 11, a release bolt 43 corresponding to the securing portion passes through
the movable lever 13 and the fixed lever 15 so as to extend along the relative rotation
axis CL, specifically, is inserted into the through holes 27 and 33 described above.
A distal end of the release bolt 43 is screwed into the fixed base 5. A head of the
release bolt 43 has a larger outer diameter than that of the through hole 27, and
is exposed on an opposite surface 13b to the one surface 13a of the movable lever
13, on which the supporting holes 19 are formed, so as to sit on the opposite surface
13b. In a portion of the cover member 37 in the vicinity of the relative rotation
axis CL, a hole for the escape of the head is provided so as not to prevent the head
of the release bolt 43 from sitting on the opposite surface 13b.
[0028] Subsequently, the functions of the brake release mechanism according to this embodiment
are described mainly referring to FIGS. 10 to 12. FIG. 12 is a view for illustrating
a plane taken along the line XII-XII in FIG. 10. The movable lever 13 and the fixed
lever 15 of the break release mechanism are provided on the side of each of the movable
bodies 3, which is opposite to the fixed base 5, as illustrated in FIGS. 10 and 11.
The movable lever 13 and the fixed lever 15 are provided to have the relation in which
the fixed lever 15 is provided on the side closer to a corresponding one of the movable
bodies 3. Further, as illustrated in FIGS. 10 to 12, the projection 3a of the corresponding
one of the movable bodies 3 is inserted between the pair of hooks 35 of the fixed
lever 15. Each of the rolling bodies 17 is located at the portion with the maximum
depth Xmax in a corresponding one of the elongated holes 21. An example of a mounting
procedure is described. First, the pair of hooks 35 of the fixed lever 15 are brought
into engagement with the projection 3a of the corresponding one of the movable bodies
3. Subsequently, the release bolt 43 is inserted into the through holes 27 and 33
to be screwed into the fixed base 5. In this manner, the head of the release bolt
43 is brought into close abutment on the opposite surface 13b of the movable lever
13.
[0029] In a state described above, the movable lever 13 is rotated as indicated by the arrow
R in FIG. 12. Then, the rotation of the fixed lever 15 in the direction of the relative
rotation is blocked by the corresponding one of the movable bodies 3 due to the engagement
between the hooks 35 and the projection 3a. Specifically, the fixed lever 15 does
not rotate, but only the movable lever 13 rotates. Therefore, the relative rotation
occurs between the movable lever 13 and the fixed lever 15.
[0030] When the relative rotation occurs between the movable lever 13 and the fixed lever
15, each of the rolling bodies 17 changes the position in synchronization with (together
with) a corresponding one of the supporting holes 19 due to the arc-like movement
of the supporting holes 19 provided on the rotating movable lever 13, and hence moves
to the portion with the minimum depth Xmin while rolling inside a corresponding one
of the elongatedholes 21. In this manner, through the movement of each of the rolling
bodies 17 from the portion with the maximum depth Xmax to the portion with the minimum
depth Xmin in a corresponding one of the elongated holes 21, the height of the part
of each of the rolling bodies 17, which is exposed from the another surface 15a of
the fixed lever 15, increases, to thereby increase the distance between the another
surface 15a of the fixed lever 15 and the one surface 13a of the movable lever 13,
specifically, the distance between the fixed lever 15 and the movable lever 13. Although
the relative rotation is allowed for the movable lever 13, the movement thereof in
the direction of the relative rotation axis CL (in particular, the movement in a direction
away from the fixed base 5) is limited by the release bolt 43. Therefore, the increase
in distance between the movable lever 13 and the fixed lever 15 appears as the movement
of the fixed lever 15 in the direction of the relative rotation axis CL away from
the movable lever 13. Therefore, the corresponding one of the movable bodies 3 is
subjected to a pressing force in the direction of the relative rotation axis CL from
the fixed lever 15 so as to move closer to the fixed base 5 against the elastic force
of the elastic body 11. As a result, one of the brake shoes 9, which is provided integrally
with the corresponding one of the movable bodies 3, separates from the inner circumferential
surface of the rotor 7 to achieve the manual release of the brake.
[0031] The relative operation of the movable lever 13 and the fixed lever 15 is appropriately
ensured by forming the collars 39 in the following mode. As illustrated in FIG. 9,
it is appropriate to set a height "X" of each of the collars 39 so as to satisfy:
where "a" represents a depth of each of the supporting holes 19 of the movable lever
13, "b" represents a thickness of the movable lever 13, and "g" represents a distance
of movement of each of the movable bodies 3, which is required to release the brake.
With setting of the height of each of the collars 39 to the value X which satisfies
the condition described above, the distance can be changed so that the movable lever
13 and the fixed lever 15 do not interfere with each other at the time of the brake
releasing operation. In addition, even in a state in which the distance between the
movable lever 13 and the fixed lever 15 increases to the maximum extent, the rolling
bodies 17 interposed therebetween can be prevented from dropping off.
[0032] As described above, according to the brake release mechanism of this embodiment,
for applying a brake releasing force to each of the movable bodies, a large frictional
force due to surface contact over a wide area is advantageously prevented from being
generated in a movable portion. More specifically, the friction generated due to the
rotation of the movable lever can be absorbed by the rotation of the rolling bodies
themselves. As aresult, effort required for the manual brake releasing operation can
be significantly reduced. Moreover, the brake can be forcibly released by only applying
a vertical turning force to the hoisting machine. Therefore, it is not necessary to
provide a large space for the releasing operation on the side of the hoisting machine,
which can lead to space saving of a hoistway and a machine room.
[0033] The present invention has been specifically described above referring to the preferred
embodiment. However, it is apparent to those skilled in the art that various modified
modes are possible based on the fundamental technological thought and teaching of
the present invention.
[0034] As an example, there may be used any securing portion, which can provide the function
of securing the position of one of the movable lever (first member) and the fixed
lever (second member) in the direction of the relative rotation axis CL without securing
the position of another thereof in the direction of the relative rotation axis CL.
Therefore, the securing portion is not limited to a single independent member as in
the embodiment described above as long as the function described above can be provided,
and may be a part of the first member or the second member, a part of the fixed base,
or a part of another element.
Reference Signs List
[0035] 3 movable body, 5 fixed base, 9 brake shoe, 13 movable lever (first member, another
of first member and second member), 13a one surface, 13b opposite surface, 15
fixed lever (second member, one of first member and second member), 15a another surface,
17 rolling body, 19
supporting hole, 21 elongated hole, 37 cover member, 39 collar, 43 release bolt (securing
portion), CL
relative rotation axis
1. A brake release mechanism for a hoisting-machine brake for an elevator, the hoisting-machine
brake including movable bodies for supporting brake shoes and a fixed base having
electromagnetic coils for driving the movable bodies, the brake release mechanism
comprising:
a first member and a second member provided so as to be rotatable relative to each
other; and
a plurality of rolling bodies provided between the first member and the second member,
wherein:
the brake release mechanism further comprises:
a plurality of supporting holes for partially housing the plurality of rolling bodies
therein, the plurality of supporting holes being formed on one of a pair of surfaces
of the first member and the second member, which face each other; and
a plurality of elongated holes each extending in an arc-like manner so as to enable
a corresponding one of the plurality of rolling bodies to move while rolling, the
plurality of elongated holes being formed on another of the pair of surfaces;
the plurality of supporting holes respectively support the plurality of rolling bodies
so as to enable the plurality of rolling bodies to spin by themselves and to move
in synchronization with the plurality of supporting holes;
each of the plurality of elongated holes is formed so that a depth for housing the
corresponding one of the plurality of rolling bodies changes when the plurality of
rolling bodies move along the plurality of elongated holes;
each of the plurality of rolling bodies is housed in both a corresponding one of the
plurality of supporting holes and a corresponding one of the plurality of elongated
holes between the first member and the second member so that a distance between the
first member and the second member in a direction of a relative rotation axis changes
in accordance with the relative rotation of the first member and the second member;
the brake release mechanism further comprises a securing portion which avoids securing
a position of one of the first member and the second member in the direction of the
relative rotation axis and secures a position of another of the first member and the
second member in the direction of the relative rotation axis;
the securing portion is fixed to the fixed base; and
the one of the first member and the second member is provided so as to apply a traveling
force in the direction of the relative rotation axis to a corresponding one of the
movable bodies.
2. A brake release mechanism according to claim 1, wherein:
rotation of the one of the first member and the second member in a direction of the
relative rotation is blocked by the corresponding one of the movable bodies; and
the plurality of elongated holes are formed on the one of the first member and the
second member.
3. A brake release mechanism according to claim 1 or 2, wherein:
the another of the first member and the second member comprises a lever-piece portion
extending in a radial direction for the relative rotation; and
the plurality of supporting holes are formed on the another of the first member and
the second member.
4. A brake release mechanism according to any one of claims 1 to 3, wherein each of the
plurality of rolling bodies comprises a spherical body.
5. A brake release mechanism according to claim 4, wherein:
at least three spherical bodies are provided as said spherical body; and
each of the plurality of supporting holes is separated from another adjacent one of
the plurality of supporting holes at an equiangular distance.
6. A brake release mechanism according to any one of claims 1 to 5, wherein the first
member and the second member are provided on a side of the corresponding one of the
movable bodies opposite to the fixed base so that the one of the first member and
the second member is located closer to the corresponding one of the movable bodies.
7. A brake release mechanism according to any one of claims 1 to 6, further comprising:
a cover member; and
a collar, wherein:
the cover member is provided so that the cover member and the one of the first member
and the second member sandwich the another of the first member and the second member
therebetween; and
the collar is provided between the cover member and the one of the first member and
the second member so as to maintain a distance between the cover member and the one
of the first member and the second member.
8. A brake release mechanism according to any one of claims 1 to 7, wherein:
the securing portion passes through the first member and the second member so as to
extend along the relative rotation axis;
a distal end of the securing portion is screwed into the fixed base; and
a head of the securing portion is exposed on an opposite surface of the another of
the first member and the second member, the opposite surface being located opposite
to one surface on which the plurality of supporting holes or the plurality of elongated
holes are formed, so that the head sits on the opposite surface.