DETAILED DESCRIPTION OF THE INVENTION

[0023] Referring to FIG. 1, a mobile storage system 10 includes a series of mobile storage units 12, each of which is mounted to a pair of tracks, one of which is shown at 14. Mobile storage system 10 is of the type generally known as a mechanical assist system, such as is available from Spacesaver Corporation of Fort Atkinson, Wis. under its Model Nos. DF MA, RG MA, or CF MA. Each mobile storage unit 12 includes an internal drive mechanism which is operable in response to rotation of an external actuator handle 16 for moving the storage unit 12 on tracks 14, in a manner as is known.

[0024] Referring to FIG. 2, the internal drive system of each mobile storage unit 12 includes an input shaft 18 which is mounted at its inner end to an input sprocket (not shown) or other input drive member. In accordance with the invention, a torque limiting coupling or mechanism 20 is interposed between input shaft 18 and actuator handle 16. In a manner to be explained, torque limiting mechanism 20 selectively couples actuator handle 16 to input shaft 18 for operating the drive system of mobile storage unit 12 for movement on tracks 14. Torque limiting mechanism 20 also selectively disengages actuator handle 16 from input shaft 18 upon application of an excessive force to actuator handle 16, such as a force exceeding the force required to move mobile storage unit 12 on tracks 14 at a maximum rate of movement or a force applied to handle 16 after storage unit 12 has reached the limit of its travel.

[0025] Torque limiting mechanism 20 generally includes a hub member 22 to which actuator handle 16 is mounted, an input member 24 mounted to input shaft 18, and a series of engagement members 26 interposed between hub member 22 and input member 24.

[0026] Referring to FIGS. 2-4, input shaft 18 is mounted at its inner end to an input or drive sprocket 28 with which a flexible drive element such as a chain 30 is engaged. Input member 24 is mounted to input shaft 18 toward the outer end of input shaft 18, such that an outer end portion 32 of input shaft 18 extends outwardly from an outer surface 34 defined by input member 24. Input shaft 18 terminates in an outer end 36, and a threaded passage 38 is formed in outer end portion 32 of input shaft 18, extending inwardly from outer end 36. Input member 24 has a disc-like shape, although it is understood that any other satisfactory shape could be employed. Input member 24 is rigidly mounted to input shaft 18 in any satisfactory manner, such as by welding.

[0027] Outer surface 34 of input member 24 is substantially flat, and a series of radially spaced recesses 40 are formed in outer surface 34. Recesses 40 are spaced an equal distance outwardly from the center of input shaft 18 and input member 24. In the illustrated embodiment, recesses 40 are in the form of passages which extend throughout the thickness of input member 24. Recesses 40 may also be formed so as to extend inwardly from outer surface 34 throughout only a portion of the thickness of input member 24.

[0028] Hub member 22 defines a central passage 44 within which outer end portion 32 of input shaft 18 is received. A recess 46 is formed in hub member 22 outwardly of central passage 44, and a shoulder 48 is formed between recess 46 and central passage 44. Hub member 22 further includes an annular outer surface 50 and a flat, annular inner surface 52.

[0029] A series of threaded actuator mounting passages 54 extend into hub member 22 from outer surface 50. Actuator handle 16 includes a series of mounting bosses 56, each of which is adapted for placement over one of actuator mounting passages 54. An opening 58 is formed in each mounting boss 56, and is located in alignment with one of actuator mounting passages 54. A threaded fastener, such as a screw 60, extends through passage 58 in each mounting boss 56 and into engagement with threads formed in the aligned actuator mounting passage 54, so as to securely and removably engage actuator handle 16 with hub member 22.

[0030] Hub member 22 further includes a series of passages 61 which extend outwardly from inner surface 52. Each passage 61 defines a reduced diameter inner section 62 which opens onto inner surface 52, and an enlarged diameter threaded outer section 64 which opens onto outer surface 50. Inner section 62 is sized so as to receive one of spherical engagement members 26 therein, such that engagement member 26 is capable of movement within inner section 62. A screw 66 is engaged with the threads of outer section 64, and a spring 68 bears between screw 66 and engagement member 26. This arrangement functions to urge engagement member 26 outwardly relative to inner surface 52 of hub member 22.

[0031] As noted previously, outer end portion 32 of input shaft 18 is received within central passage 44 of hub member 22. A washer 70 is engaged with outer end 36 of input shaft 18, and overlies shoulder 48 defined by hub member 22. A screw 72 is engaged with threaded passage 38 extending inwardly from outer end 36 of input shaft 18, so as to maintain washer 70 in engagement with outer end 36 of input shaft 18.

[0032] In operation, torque limiting mechanism 20 functions as follows to prevent transfer of a force exceeding a predetermined threshold from actuator handle 16 to input shaft 18, to thereby isolate the drive system of mobile storage unit 12 from application of such a force and the resultant adverse effects.

[0033] Engagement members 26 are normally positioned as illustrated in FIG. 4, in an engaged position in which each engagement member 26 is seated against the outer edge of one of recesses 40 in input member 24, i.e. in engagement with the edge defined between outer surface 34 and the wall of recess 40. Recess 40 has a diameter less than that of engagement member 26, so as to prevent engagement member 26 from moving into recess 40. With this arrangement, each engagement member 26 engages the edge of recess 40 outwardly of the center of engagement member 26. Spring 68 and set screw 72 function to bias engagement member 26 against the engagement structure defined by passage 40 in input member 24, and engagement members 26 are thus operable to couple hub member 22 to input member 24. In normal operation, rotation of handle 16 results in rotation of hub member 22, and engagement members 26 function to rotate input member 24 along with hub member 22. Such rotation of input member 24 results in rotation of input shaft 18, to provide input power to the drive system of mobile storage unit 12 and to thereby move mobile storage unit 12 in a conventional manner.

[0034] When a force exceeding a predetermined threshold is applied to actuator handle 16 and thereby to hub member 22, such force is transferred to engagement members 26 which unseats engagement members 26 from recesses 40 due to the curvature of the portion of engagement members 26 received within recesses 40. Engagement members 26 are thus moved to the disengaged position of FIG. 5 when engagement members 26 are unseated from recesses 40 in input member 24, to decouple hub member 22 from input member 24. When input member 24 and hub member 22 are de-coupled in this manner, hub member 22 spins on the outer end portion 32 of input shaft 18 while the force applied to handle 16 remains above the predetermined threshold. In this manner, the excessive force is not transferred to input shaft 18, and thus does not adversely impact the components of mobile storage unit 12. The threshold force for moving engagement members 26 to the disengaged position of FIG. 5 may be selected according to the maximum force required to move mobile storage unit 12 at its maximum rate of movement, or by the amount of force otherwise known to damage or cause malfunction of the components of mobile storage unit 12, such as the chain tensioning mechanism, e.g. when a force is applied to handle 16 after mobile storage unit 12 has reached the limit of its travel.

[0035] To return engagement members 26 to the engaged position as shown in FIG. 4, the operator continues rotation of actuator handle 16 in either a clockwise or a counterclockwise direction, until engagement members 26 are once again seated in recesses 40, and the applied force falls below the threshold. As can be appreciated, recesses 40 are spaced relatively close together, such that a relatively small amount of travel of actuator handle 16 relative to input shaft 18 is required to seat engagement members 26 in recesses 40. The operator then again applies a force to actuator handle 16 less than the threshold force engagement to maintain members 26 in the engaged position, to impart movement to mobile storage unit 12.

[0036] The amount of biasing force exerted by each spring 68 on its respective engagement member 26 can be adjusted by moving set screw 72 within outer section 64 of passage 61. Set screw 72 is turned into passage 61 to increase the threshold, and is moved out of passage 61 to decrease the threshold. Adjustments can easily be made after removing actuator handle 16 by disengaging screws 60 from passages 61.

[0037] In another embodiment illustrated in FIGS. 6 and 7, torque limiting coupling or mechanism 20 is in the form of a slip disc 76 located between hub member 22 and input member 24. In this version, recesses 40 in input member outer surface 34 are eliminated, as are passages 51 in hub member 22. Slip disc 76 is positioned between and engaged with input member outer surface 34 and hub member inner surface 52, and is operable to selectively couple hub member 22 and input member 24. In a preferred form, slip disc 76 is constructed of a friction washer material such as is available from Friction Material Corporation of Huntington, Ind. under its designation NA-104, although it is understood that other similar types of materials may be employed. Slip disc 76 is formed with a central opening 78, which is located in alignment with central passage 44 of hub member 22 and through which outer end portion 32 of input shaft 18 extends. Slip disc 76 is constructed so as to cover substantially the entirety of input member outer surface 34 and the facing hub member inner surface 52.

[0038] As in the embodiment of FIGS. 2-5, outer end 36 of input shaft 18 includes threaded passage 38, which is adapted to receive the threaded shank of screw 72 for securing hub member 22 and input member 24 together. In this version, a pair of Belleville-type spring washers 80 are placed between the head of screw 72 and outer end 36 of input shaft 18. Spring washers 80 bear on an annular outwardly facing surface 82 defined by hub member 22 and located outwardly of input shaft outer end portion 32. Spring washers 80 function in a known manner to urge hub member 22 into engagement with input member 24. When the threaded shank of screw 72 is advanced into threaded passage 38, the head of screw 72 engages spring washers 80, and the degree of advancement of screw 72 relative to input shaft 18 controls the amount of biasing force exerted by spring washers 80 on hub member 22. With slip disc 76 located between hub member 22 and input member 24, the biasing force applied by spring washers 80 urges inner surface 52 of hub member 22 into engagement with the outer surface of slip disc 76, and in turn urges the inner surface of slip disc 76 against outer surface 34 of hub member 24.

[0039] In normal operation, hub member 22 is rotated in response to application of a manual force to actuator handle 16, and rotation of hub member 22 is transferred to input member 24 through the frictional engagement of slip disc 76 between hub member 22 and input member 24. When the torque applied to actuator handle 16 exceeds a predetermined threshold, as determined by the characteristics of slip disc 76 and the degree of biasing force applied to slip disc 76 by spring washers 80, the frictional engagement provided by slip disc 76 is overcome such that hub member 22 spins freely relative to input member 24 and torque is not transferred from hub member 22 to input member 24. When the torque applied to actuator handle 16 falls below the predetermined threshold, slip disc 76 once again functions to couple hub member 22 and input member 24, to transfer rotational input force from hub member 22 to input member 24.

[0040] To adjust the threshold at which frictional engagement of hub member 22 with input member 24 through slip disc 76 is overcome, the user adjusts the degree of advancement of the shank of screw 72 within passage 38, to adjust the biasing force exerted by spring washers 80 on hub member 22. A greater degree of advancement increases the biasing force applied by spring washers 80 so as to increase the degree of frictional engagement of hub member 22 within input member 24 through slip disc 76, to increase the threshold beyond which slip disc 76 ceases to transfer torque from hub member 22 to input member 24. Conversely, a lesser degree of advancement of the threaded shank of screw 72 within passage 38 results in a lessening of the biasing force applied to hub member 22 by spring washers 80, to lower the threshold beyond which slip disc 76 does not transfer torque from hub member 22 to input member 24.

[0041] It can thus be appreciated that slip disc 76 provides the same torque transferring and limiting function as the embodiment of FIGS. 2-5, without the need for engagement members 26 and the associated recesses 40, passages 62, springs 68 and screws 66. This embodiment reduces the cost and labor associated with torque limiting mechanism 20.

[0042] FIGS. 8a and 8b illustrate movement of mobile storage units 12 on tracks 14. In a manner as is known, drive chain 30 is engaged with input sprocket 28 at its upper end and with a driven sprocket, shown at 74, at its lower end. Driven sprocket 74 in turn is engaged with a drive shaft 76, which imparts rotation to the drive system components which move mobile storage unit 12 on tracks 14 in a conventional manner.

[0043] It can thus be appreciated that a torque limiting mechanism 20 functions to couple the actuator handle 16 to the input shaft 18 when an actuating force below a certain threshold is applied to the actuator handle 16. The torque limiting mechanism 20 functions to de-couple the actuator handle 16 from the input shaft 18 when an excessive force is applied to the actuator handle 16 to isolate the components of the drive system from excessive force. Torque limiting mechanism 20 is relatively simple in its construction and operation, yet provides a highly effective means for protecting the components of the mobile storage unit drive system. A torque limiting mechanism 20 may be a component of original manufacture or may be retrofitted in the field to existing, previously installed mobile storage units 12.

[0044] It should be understood that the specific embodiments of the present invention shown are representative of the types of torque limiting mechanisms which may be employed for preventing application of an excessive force to the components of the drive system driven by input shaft 18. For example, another type of torque limiting mechanism, e.g. an overrunning clutch, may be used, and the torque limiting mechanism may be located at any position in the drive system of mobile storage system 10, such as between input shaft 18 and drive sprocket 28. Torque limiting mechanism 20 is therefore not limited to the specific location shown and described.

[0045] Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.