US3897077A - Safety ski binding having cable held sole plate - Google Patents

Safety ski binding having cable held sole plate Download PDF

Info

Publication number
US3897077A
US3897077A US436544A US43654474A US3897077A US 3897077 A US3897077 A US 3897077A US 436544 A US436544 A US 436544A US 43654474 A US43654474 A US 43654474A US 3897077 A US3897077 A US 3897077A
Authority
US
United States
Prior art keywords
ski
cable
sole plate
plate
safety
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US436544A
Inventor
Gottfried Schweizer
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Gertsch AG
Original Assignee
Gertsch AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Gertsch AG filed Critical Gertsch AG
Application granted granted Critical
Publication of US3897077A publication Critical patent/US3897077A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • AHUMAN NECESSITIES
    • A63SPORTS; GAMES; AMUSEMENTS
    • A63CSKATES; SKIS; ROLLER SKATES; DESIGN OR LAYOUT OF COURTS, RINKS OR THE LIKE
    • A63C9/00Ski bindings
    • A63C9/08Ski bindings yieldable or self-releasing in the event of an accident, i.e. safety bindings
    • A63C9/086Ski bindings yieldable or self-releasing in the event of an accident, i.e. safety bindings using parts which are fixed on the shoe of the user and are releasable from the ski binding

Definitions

  • ABSTRACT Safety release ski binding engaging the bottom center of a boot.
  • a safety release binding wherein a sole plate is fitted forwardly and rearwardly with conventional boot sole engaging means. Said plate is then fixed removably to a ski by being provided with openings therein which fit over suitable, as conical or ball shaped, abutments projecting upwardly from the upper ski surface. The plate is held down against the ski and onto said abutments by an anchor disk which can slide longitudinally of said plate and rotate with respect thereto but which is held against movement perpendicular with respect thereto.
  • a cable is fastened at one end to said disk, passes through a guide on said ski and is fixed at its other end to manually operable safety tensioning means.
  • said cable holds the plate and hence the ski boot tightly down against the ski and said abutments prevent movement thereof with respect to the ski. In a fall, however, sufficient force is applied to the cable to effect release of the tensioning means.
  • the plate (10) then leaves the ski but the cable continues to function as a safety strap to prevent escape of the ski from the skier.
  • the invention relates to a safety ski binding having a cable or the like which is connected at one end to the ski boot and at the other end to a release mechanism and wherein stops on the ski boot abut shoulders fixed to the ski.
  • a cable is for example suspended at one end in a boot fitting and is connected at its other end to a rotatably supported drum.
  • the cable is constantly maintained under tension by a spiral spring which is installed in the drum.
  • a pivotable lever is supported in the housing and one end of such lever engages a slot of the drum.
  • the lever is loaded by a torsion spring which is of greater strength than that of the spiral spring and therefore serves as a release spring.
  • a disadvantage of this arrangement lies in that it is difficult to place the ski boot properly in the binding.
  • the one end of the cable must extend into a corresponding slot of the boot fitting.
  • the boot fitting may be damaged during walking and snow, ice, dirt or the like can accumulate in the slot. Further, snow, ice, dirt or the like can penetrate between ski boot and ski whereby a secure frictional connection between boot and ski or between the binding parts is no longer assured.
  • this type of binding a considerable likelihood of breakdown.
  • the purpose of the invention is to avoid these disadvantages and the invention is characterized in that the ski boot is held in a known manner on a sole plate, on which engages a cable or the like which is movably supported in a guide and further in that the shoulders fixed to the ski are for example cone-shaped or ball-shaped pins or the like, which engage stops formed by recesses in the sole plate and do so in response to a tensioned release mechanism.
  • a further advantage consists in that by suitably arranging a sole plate, an adjustable heel holder for various boot sizes can be used without changing the position of the safety elements.
  • FIGS. 1 and 2 illustrate a safety ski binding embody ing the invention wherein FIG. 1 is a partial central cross-sectional view and FIG. 2 is a side view, but wherein the sole plate has been lifted off and is illustrated in a plan view from below.
  • a ski boot 1 is secured by means of a toe piece 2 and an adjustable heel piece 3 on a sole plate 4.
  • the sole plate 4 has recesses 5 into which engage pins 8, here of conical shape, which are mounted on the ski 6 through a base plate 7.
  • a slotted hole 9 is provided in the sole plate 4, in which slotted hole a disk 10 is supported against perpendicular movement with respect thereto. but in a manner to permit parallel sliding and rotation.
  • a cable 11 is secured at one end on the disk 10, which cable slides in a guide 12 on the base plate 7 and engages by its other end an eyelet 13 of a safety tensioning means 14.
  • the sole plate 4 has bores 15 into which the heel piece 3 can be connected accordingto the ski boot size.
  • the invention is not limited to the illustrated exem plary embodiment. A number of further embodiments exist which lie within the scope of the invention. For example in place of the pins, webs could be provided which engage corresponding recesses of the sole plate. Further, a stop or marking may be provided on the ski which facilitates the placing of the standing plate on the pin.
  • a safety ski binding arrangement for securing a ski boot to a ski comprising:
  • a sole plate having means thereon for securing said ski boot thereto, said sole plate including guide means thereon;
  • releasable securing means for releasably securing said sole plate to said ski
  • said releasable securing means comprising nonelastic cable secured at one end to the underside of said carriage means, lever operated tensioning and release means secured to said ski, the opposite end of said cable being secured to said lever operated tensioning and release means, cable guide means for guiding said cable downwardly from said sole plate and in the plane between the sole plate and the ski to said lever operated tensioning and release means;
  • stop means for engaging and positioning said sole plate on said ski prior to a tensioning of said cable, whereby a tensioning of said cable by said lever operated tensioning and release means will tighten said cable and draw said sole plate into tight engagement with said stop means.
  • a safety ski binding arrangement according to claim 1, wherein said sole plate is a flat plate;
  • said stop means includes a plurality of recesses in the bottom of said sole plate and a corresponding number of pins mounted on the upper surface of said ski and projecting upwardly therefrom, said pins being received in said recesses on said sole plate.
  • pins have a tapered surface portion corresponding to said internal tapered surface portion so that said surfaces are parallel when in engagement with each other.
  • said guide means comprises an elongated slotted hole in the bottom of said flat plate, the axis of elongation extending parallel to the longitudinal axis of said flat plate;
  • said carriage means comprises a disk capable of reciprocating movement back and forth in said slotted hole and rotation about its own axis, the axis of said disk being perpendicular to the plane of said flat plate;
  • said cable is secured at said one end to said disk; and i wherein said disk is located intermediate the ends of said slotted hole when said cable is tightened and said stop means engages and positions said flat plate on said ski.

Landscapes

  • Footwear And Its Accessory, Manufacturing Method And Apparatuses (AREA)

Abstract

Safety release ski binding engaging the bottom center of a boot. There is provided a safety release binding wherein a sole plate is fitted forwardly and rearwardly with conventional boot sole engaging means. Said plate is then fixed removably to a ski by being provided with openings therein which fit over suitable, as conical or ball shaped, abutments projecting upwardly from the upper ski surface. The plate is held down against the ski and onto said abutments by an anchor disk which can slide longitudinally of said plate and rotate with respect thereto but which is held against movement perpendicular with respect thereto. A cable is fastened at one end to said disk, passes through a guide on said ski and is fixed at its other end to manually operable safety tensioning means. In normal use, said cable holds the plate and hence the ski boot tightly down against the ski and said abutments prevent movement thereof with respect to the ski. In a fall, however, sufficient force is applied to the cable to effect release of the tensioning means. The plate (10) then leaves the ski but the cable continues to function as a safety strap to prevent escape of the ski from the skier.

Description

United States Patent [191 Schweizer July 29, 1975 [75] Inventor:
[73] Assignee:
Gottfried Schweizer. Vienna, Austria Gertsch AG. Zug, Switzerland 22 Filed: Jan. 25, 1974 [21] Appl. No.: 436,544
[30] Foreign Application Priority Data Feb. 6, 1973 Austria 1053/73 [52] U.S. Cl 280/11.35 K; 280/11.35 N [51] Int. Cl. A63c 9/08 [58] Field of Search 280/1l.35 D, 11.35 C, 2230/] 1.35 K, 11.35 F, 11.35 P, 11.35 R. 280/1 1.35 N
[56] References Cited UNITED STATES PATENTS 2,685,448 8/1954 Walker 280/1 1.35 T 3,145,027 8/1964 Berchtold et a1. 280/1 1.35 Y 3,494,628 2/1970 Spademan 280/1 1.35 D 3,764,154 10/1973 Witting 280/1 1.35 N 3,775,866 12/1973 Marker 280/1 1.35 K
FOREIGN PATENTS OR APPLICATIONS 1,179,625 12/1958 France 280/1 1.35 C 1,923,001 4/1970 Germany 280/1 1.35
Primary ExaminerDavid Schonberg Assistant Examiner-David M. Mitchell Attorney, Agent, or Firm--Woodhams, Blanchard and Flynn [57] ABSTRACT Safety release ski binding engaging the bottom center of a boot. There is provided a safety release binding wherein a sole plate is fitted forwardly and rearwardly with conventional boot sole engaging means. Said plate is then fixed removably to a ski by being provided with openings therein which fit over suitable, as conical or ball shaped, abutments projecting upwardly from the upper ski surface. The plate is held down against the ski and onto said abutments by an anchor disk which can slide longitudinally of said plate and rotate with respect thereto but which is held against movement perpendicular with respect thereto. A cable is fastened at one end to said disk, passes through a guide on said ski and is fixed at its other end to manually operable safety tensioning means. In normal use, said cable holds the plate and hence the ski boot tightly down against the ski and said abutments prevent movement thereof with respect to the ski. In a fall, however, sufficient force is applied to the cable to effect release of the tensioning means. The plate (10) then leaves the ski but the cable continues to function as a safety strap to prevent escape of the ski from the skier.
4 Claims, 2 Drawing Figures SAFETY SKI BINDING HAVING CABLE HELD SOLE PLATE FIELD OF THE INVENTION The invention relates to a safety ski binding having a cable or the like which is connected at one end to the ski boot and at the other end to a release mechanism and wherein stops on the ski boot abut shoulders fixed to the ski.
BACKGROUND OF THE INVENTION In a known safety ski binding of this type, a cable is for example suspended at one end in a boot fitting and is connected at its other end to a rotatably supported drum. The cable is constantly maintained under tension by a spiral spring which is installed in the drum. A pivotable lever is supported in the housing and one end of such lever engages a slot of the drum. The lever is loaded by a torsion spring which is of greater strength than that of the spiral spring and therefore serves as a release spring. Through this arrangement, the fitting of the ski boot is urged against a projection on the housing and the ski boot is thus held on the ski.
A disadvantage of this arrangement lies in that it is difficult to place the ski boot properly in the binding. The one end of the cable must extend into a corresponding slot of the boot fitting. It is also possible that the boot fitting may be damaged during walking and snow, ice, dirt or the like can accumulate in the slot. Further, snow, ice, dirt or the like can penetrate between ski boot and ski whereby a secure frictional connection between boot and ski or between the binding parts is no longer assured. Thus there exists in this type of binding a considerable likelihood of breakdown.
SUMMARY OF THE INVENTION The purpose of the invention is to avoid these disadvantages and the invention is characterized in that the ski boot is held in a known manner on a sole plate, on which engages a cable or the like which is movably supported in a guide and further in that the shoulders fixed to the ski are for example cone-shaped or ball-shaped pins or the like, which engage stops formed by recesses in the sole plate and do so in response to a tensioned release mechanism.
Through this construction, the user can enter into or be released from the ski binding without operating or releasing the safety mechanism. Also it is not possible to damage the pins on the ski during transporting of the ski because they remain at all times firmly connected to the sole plate. By arranging a tensioning means as a release mechanism the susceptibility to breakdown is almost completely avoided. A further advantage consists in that by suitably arranging a sole plate, an adjustable heel holder for various boot sizes can be used without changing the position of the safety elements.
BRIEF DESCRIPTION OF THE DRAWINGS The subject matter of the invention is exemplarily illustrated in one embodiment in the drawing, in which:
FIGS. 1 and 2 illustrate a safety ski binding embody ing the invention wherein FIG. 1 is a partial central cross-sectional view and FIG. 2 is a side view, but wherein the sole plate has been lifted off and is illustrated in a plan view from below.
DETAILED DESCRIPTION As shown in the drawing, a ski boot 1 is secured by means of a toe piece 2 and an adjustable heel piece 3 on a sole plate 4. The sole plate 4 has recesses 5 into which engage pins 8, here of conical shape, which are mounted on the ski 6 through a base plate 7. Furthermore a slotted hole 9 is provided in the sole plate 4, in which slotted hole a disk 10 is supported against perpendicular movement with respect thereto. but in a manner to permit parallel sliding and rotation. A cable 11 is secured at one end on the disk 10, which cable slides in a guide 12 on the base plate 7 and engages by its other end an eyelet 13 of a safety tensioning means 14. As already known, the sole plate 4 has bores 15 into which the heel piece 3 can be connected accordingto the ski boot size. By using the disk, the same stress directions of the cable are always obtained during forward, backward and twisting falls and thus substantially constant frictional relationships are also obtained.
If a safety release occurs, the recesses 5 of the sole plate release from the pin 8 and the disk 10 pulls the cable 11 against the force of the spring of the safety tensioning means 14 and causes same to open. (See also FIG. 1 of US. Pat. No. 3,190,667.) Thus the ski boot 1 with the sole plate 4 is completely freed from the ski 6 and the cable 11 now serves with respect thereto only as a catch mechanism. After a release, the ski boot 1 together with the sole plate with the recesses 5 may be replaced onto the pins 8, the lever of the safety tensioning means 14 again moved. forwardly and the safety ski binding is again ready to be used.
The invention is not limited to the illustrated exem plary embodiment. A number of further embodiments exist which lie within the scope of the invention. For example in place of the pins, webs could be provided which engage corresponding recesses of the sole plate. Further, a stop or marking may be provided on the ski which facilitates the placing of the standing plate on the pin.
Although a particular preferred embodiment of the invention has been disclosed above for illustrative purposes, it will be understood that variations or modifications thereof which Iie within the scope of the appended claims are fully contemplated.
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A safety ski binding arrangement for securing a ski boot to a ski, comprising:
a sole plate having means thereon for securing said ski boot thereto, said sole plate including guide means thereon;
carriage means reciprocably mounted in said guide means for movement in the plane defined by the sole plate;
releasable securing means for releasably securing said sole plate to said ski, said releasable securing means comprising nonelastic cable secured at one end to the underside of said carriage means, lever operated tensioning and release means secured to said ski, the opposite end of said cable being secured to said lever operated tensioning and release means, cable guide means for guiding said cable downwardly from said sole plate and in the plane between the sole plate and the ski to said lever operated tensioning and release means; and
stop means for engaging and positioning said sole plate on said ski prior to a tensioning of said cable, whereby a tensioning of said cable by said lever operated tensioning and release means will tighten said cable and draw said sole plate into tight engagement with said stop means.
2. A safety ski binding arrangement according to claim 1, wherein said sole plate is a flat plate;
wherein said stop means includes a plurality of recesses in the bottom of said sole plate and a corresponding number of pins mounted on the upper surface of said ski and projecting upwardly therefrom, said pins being received in said recesses on said sole plate.
3. A safety ski binding arrangement according to claim 2, wherein said recesses have an internal tapered surfaceportion; and
wherein said pins have a tapered surface portion corresponding to said internal tapered surface portion so that said surfaces are parallel when in engagement with each other.
4. A safety ski binding arrangement according to claim 2, wherein said guide means comprises an elongated slotted hole in the bottom of said flat plate, the axis of elongation extending parallel to the longitudinal axis of said flat plate;
wherein said carriage means comprises a disk capable of reciprocating movement back and forth in said slotted hole and rotation about its own axis, the axis of said disk being perpendicular to the plane of said flat plate; and
wherein said cable is secured at said one end to said disk; and i wherein said disk is located intermediate the ends of said slotted hole when said cable is tightened and said stop means engages and positions said flat plate on said ski.

Claims (4)

1. A safety ski binding arrangement for securing a ski boot to a ski, comprising: a sole plate having means thereon for securing said ski boot thereto, said sole plate including guide means thereon; carriage means reciprocably mounted in said guide means for movement in the plane defined by the sole plate; releasable securing means for releasably securing said sole plate to said ski, said releasable securing means comprising nonelastic cable secured at one end to the underside of said carriage means, lever operated tensioning and release means secured to said ski, the opposite end of said cable beinG secured to said lever operated tensioning and release means, cable guide means for guiding said cable downwardly from said sole plate and in the plane between the sole plate and the ski to said lever operated tensioning and release means; and stop means for engaging and positioning said sole plate on said ski prior to a tensioning of said cable, whereby a tensioning of said cable by said lever operated tensioning and release means will tighten said cable and draw said sole plate into tight engagement with said stop means.
2. A safety ski binding arrangement according to claim 1, wherein said sole plate is a flat plate; wherein said stop means includes a plurality of recesses in the bottom of said sole plate and a corresponding number of pins mounted on the upper surface of said ski and projecting upwardly therefrom, said pins being received in said recesses on said sole plate.
3. A safety ski binding arrangement according to claim 2, wherein said recesses have an internal tapered surface portion; and wherein said pins have a tapered surface portion corresponding to said internal tapered surface portion so that said surfaces are parallel when in engagement with each other.
4. A safety ski binding arrangement according to claim 2, wherein said guide means comprises an elongated slotted hole in the bottom of said flat plate, the axis of elongation extending parallel to the longitudinal axis of said flat plate; wherein said carriage means comprises a disk capable of reciprocating movement back and forth in said slotted hole and rotation about its own axis, the axis of said disk being perpendicular to the plane of said flat plate; and wherein said cable is secured at said one end to said disk; and wherein said disk is located intermediate the ends of said slotted hole when said cable is tightened and said stop means engages and positions said flat plate on said ski.
US436544A 1973-02-06 1974-01-25 Safety ski binding having cable held sole plate Expired - Lifetime US3897077A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
AT105373A AT318449B (en) 1973-02-06 1973-02-06 Safety bindings

Publications (1)

Publication Number Publication Date
US3897077A true US3897077A (en) 1975-07-29

Family

ID=3505560

Family Applications (1)

Application Number Title Priority Date Filing Date
US436544A Expired - Lifetime US3897077A (en) 1973-02-06 1974-01-25 Safety ski binding having cable held sole plate

Country Status (4)

Country Link
US (1) US3897077A (en)
AT (1) AT318449B (en)
CA (1) CA994827A (en)
CH (1) CH577834A5 (en)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2397206A1 (en) * 1977-07-15 1979-02-09 Marker Hannes SAFETY SKI BINDING
US4169612A (en) * 1976-10-07 1979-10-02 Bernhard Kirsch Ski bindings
US6322095B1 (en) * 1998-06-15 2001-11-27 Bryce Wheeler Release binding for telemark and cross-country skis
US20070045989A1 (en) * 2005-08-29 2007-03-01 The Burton Corporation Strap for snowboard boots or bindings
US20070045988A1 (en) * 2005-08-29 2007-03-01 The Burton Corporation Strap for snowboard boots or bindings
US20070045990A1 (en) * 2005-08-29 2007-03-01 The Burton Corporation Strap for snowboard boots or bindings
US20140103621A1 (en) * 2012-10-11 2014-04-17 Salomon S.A.S. Device and assembly for gliding
USD851189S1 (en) * 2016-02-12 2019-06-11 Joachim Lennart Grenestedt Ski suspension system

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2685448A (en) * 1950-11-21 1954-08-03 Robert A Walker Ski and binding therefor
US3145027A (en) * 1961-02-06 1964-08-18 Berchtold Ludwig Safety ski binding
US3494628A (en) * 1967-02-24 1970-02-10 Spademan Richard George Toe piece
US3764154A (en) * 1970-06-15 1973-10-09 G Witting Safety ski binding
US3775866A (en) * 1971-03-25 1973-12-04 Marker Hannes Stabilizer for boots for crosscountry skiing

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2685448A (en) * 1950-11-21 1954-08-03 Robert A Walker Ski and binding therefor
US3145027A (en) * 1961-02-06 1964-08-18 Berchtold Ludwig Safety ski binding
US3494628A (en) * 1967-02-24 1970-02-10 Spademan Richard George Toe piece
US3764154A (en) * 1970-06-15 1973-10-09 G Witting Safety ski binding
US3775866A (en) * 1971-03-25 1973-12-04 Marker Hannes Stabilizer for boots for crosscountry skiing

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4169612A (en) * 1976-10-07 1979-10-02 Bernhard Kirsch Ski bindings
FR2397206A1 (en) * 1977-07-15 1979-02-09 Marker Hannes SAFETY SKI BINDING
US4203614A (en) * 1977-07-15 1980-05-20 Hannes Marker Safety ski binding
US6322095B1 (en) * 1998-06-15 2001-11-27 Bryce Wheeler Release binding for telemark and cross-country skis
US7516976B2 (en) 2005-08-29 2009-04-14 The Burton Corporation Strap for snowboard boots or bindings
US20070045988A1 (en) * 2005-08-29 2007-03-01 The Burton Corporation Strap for snowboard boots or bindings
US20070045990A1 (en) * 2005-08-29 2007-03-01 The Burton Corporation Strap for snowboard boots or bindings
US7306241B2 (en) 2005-08-29 2007-12-11 The Burton Corporation Strap for snowboard boots or bindings
US20070045989A1 (en) * 2005-08-29 2007-03-01 The Burton Corporation Strap for snowboard boots or bindings
US20090152835A1 (en) * 2005-08-29 2009-06-18 The Burton Corporation Strap for snowboard boots or bindings
US7669880B2 (en) 2005-08-29 2010-03-02 The Burton Corporation Strap for snowboard boots or bindings
US7694994B2 (en) 2005-08-29 2010-04-13 The Burton Corporation Strap for snowboard boots or bindings
US7766364B2 (en) 2005-08-29 2010-08-03 The Burton Corporation Strap for snowboard boots or bindings
US20140103621A1 (en) * 2012-10-11 2014-04-17 Salomon S.A.S. Device and assembly for gliding
US9242166B2 (en) * 2012-10-11 2016-01-26 Salomon S.A.S. Device and assembly for gliding
USD851189S1 (en) * 2016-02-12 2019-06-11 Joachim Lennart Grenestedt Ski suspension system

Also Published As

Publication number Publication date
AT318449B (en) 1974-10-25
CA994827A (en) 1976-08-10
CH577834A5 (en) 1976-07-30

Similar Documents

Publication Publication Date Title
US4348036A (en) Safety binding for nordic skis
US4728116A (en) Releasable binding for snowboards
US3606370A (en) Safety binding mechanism
US2836428A (en) Ski binding having swivelable heel securing means
US5318320A (en) Snow ski binding
US3897077A (en) Safety ski binding having cable held sole plate
US4261595A (en) Ski boot heel lock
JPH02502700A (en) Safety key bindings for athletic equipment
US3797841A (en) Safety binding
US4632419A (en) Ski binding
US3953042A (en) Touring ski boot heel binding
US3884492A (en) Overcenter ski binding mechanism
US4288093A (en) Sole-support mechanism for the sole of a ski boot
US6196559B1 (en) Snowboot binding
US3771806A (en) Safety binding for skis
US6527293B1 (en) Binding for a snow-sport device
US3448989A (en) Retaining device for safety ski bindings
US4131963A (en) Ski binding
US3863942A (en) Ski binding
US4779890A (en) Equipment for a monoski
US3743308A (en) Ski binding
US2959424A (en) Ski binding
US2868555A (en) Releasable ski binding
US2954236A (en) Ski binding having releasable heel securing means
CA1069143A (en) Heel binding for trail skis