US3228659A

US3228659A - Lifting apparatus

Info

Publication number: US3228659A
Application number: US309796A
Authority: US
Inventors: Sturm Horst-Ernst
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-10-26
Filing date: 1963-09-18
Publication date: 1966-01-11
Anticipated expiration: 1983-01-11
Also published as: DE1166991B

Description

Jan. 11, 1966 HORST-ERNST STURM 3,223,659

LIFTING APPARATUS Filed Sept. 18, 1963 4 Sheets-Sheet 1 Jan. 11, 1966 HORSTERNST STURM 3,

LIFTING APPARATUS 4 Sheets-Sheet 5 Filed Sept. 18, 1963 1966 HORST-ERNST STURM 3,

LIFTING APPARATUS Filed Sept. 18, 1963 4 Sheets-Sheet 4 I x L United States Patent "ice 3,228,659 LIFTING APPARATUS Horst-Ernst Storm, 6200 Bodenstedtstrasse 5, Wiesbaden, Germany Filed Sept. 18, 1963, Ser. No. 309,796 Claims priority, application Germany, Sept. 20, 1962, M 42,521; Oct. 26, 1962, T 22,919; Oct. 27, 1962, T 15,300; Nov. 27, 1962,1 15,393; Feb. 22, 1963,

16 Claims. (c1. 2s4 122 The present invention relates to lifting apparatus in general, and more particularly to an improved hydraulic lifting apparatus which is especially suited for moving large plate-like workpieces to and from a treating station in various types of processing machines, for stacking plate-like and otherwise shaped workpieces, for loading or unloading of vehicles, for storing of heavy objects, for removing heavy objects from storage and for many similar purposes. Such lifting apparatus normally comprise a load-supporting platform which is movable in parallelism with itself toward and away from a base between two end positions and through a desired number of intermediate positions at a selected level above the base.

It is an important object of the present invention to provide a lifting apparatus of the above outlined characteristics which embodies one or more novel safety devices arranged to prevent damage to the apparatus and/or injury to workmen.

Another object of the invention is to provide a lifting apparatu wherein the platform is raised or lowered by means of oil or another suitably hydraulic fluid and wherein all of the safety devices are operated in a fully automatic way in response to movements of the platform toward or away from its base.

A further object of the invention is to provide a lifting apparatus wherein the platform is automatically arrested when a rigid object or the limb of an operator happens to be located above the base while the platform descends to its lower end position.

An additional object of the invention is to provide a hydraulic lifting apparatus of the above outlined characteristics wherein the pressure relief valve (which is a standard component of such hydraulic apparatus) is regulated in a fully automatic way so that its resistance to flow of hydraulic fluid always exceeds only slightly the pressure which is necessary for proper operation of the apparatus.

Still another object of the invention is to provide a hydraulic lifting apparatus wherein all movements of the platform are controlled in such a way that the speed of the platform to its lower end position is not affected by its own weight and by the fact that the platform might be empty or that the platform supports a substantial load.

A concomitant object of the invention is to provide a series of automatic safety devices which prevent excessive movements of the platform in a direction away from the base of my improved lifting apparatus so that the platform is arrested even if one safety device happens to be damaged or fails to respond for another reason which is beyond the control of the operator.

A further object of the instant invention is to provide a fully automatic hydraulically operated lifting apparatus wherein the movements of a horizontal platform between and into its end positions may be initiated by remote control and in any desired sequence so that the lifting apparatus may be combined with one or more additional machines to lift or lower loads in synchronism with the operation of such additional machine or machines.

Still another object of my invention is to provide a lifting apparatus wherein all component parts serving to initiate and control movements of the platform are fully 3,228,659 Patented Jan. 11, 1966 concealed at least when the platform assumes its lower end position so that the entire apparatus forms a very compact structure which occupies little room when not in use and that all of its delicate elements are fully protected not only from physical damage but also against corrosion and similar influences.

With the above objects in view, one feature of my invention resides in the provision of a hydraulic lifting apparatus which comprises a base, a plurality of moving parts including a load-supporting platform and supporting means operatively connected with the platform and with the base and arranged to move the platform between two end positions toward and away from the base, hydraulic operating means including a source of hydraulic fluid, a jack or a similar lifting device connected with one of the moving parts, and supply conduit means connecting the source with the lifting device and containing a pump which delivers fluid from the source to the lifting device so that the latter may move the platform to its upper end position, and a safety device including return conduit means connected with the supply conduit means and/or with the lifting device and a normally closed safety valve in the return conduit means. This safety valve is located in the path of a moving part so that it opens automatically and permits return flow of fluid from the lifting device to the source when the platform assumes a position at a predetermined distance from the base. inversely, it is equally possible to use a stationary actuating device and to mount the safety valve on one of the moving parts so that the valve actually shares some or all movements of the platform.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved lifting apparatus itself, however, both as to its construction and its mode of operation, together withadditional features and advantages thereof, will be best understood from the following de tailed description of certain specific embodiments with reference to the accompanying drawings, in which:.

FIG. 1 is a longitudinal vertical section through a lifting apparatus which embodies one form of the present invention, the platform of the lifting apparatus being shown in raised position and the section of FIG. 1 being taken in the direction of arrows as seen from the line II of FIG. 2;

FIG. 2 is a horizontal section as seen in the direction of arrows from the line IIII of FIG.v l;

FIG. 3 is a schematic diagram showing the hydraulic and electric circuitry of the lifting apparatus;

FIG. .4 is a fragmentary diagrammatic view of an adjustable pressure relief valve which may be used in the lifting apparatus of FIGS. 1 to 3.; i l V FIG. 5 is a diagrammatic view of the hydraulic and electric circuitry in a modified lifting apparatus which is provided with a volume governorfor accurately regulating the rate ofspeed at which the platform descends. to its lower end position; V 7

FIG. 6 is a transverse section through an elastic tube which constitutes one element of a safety devicefor the lifting apparatus of the present invention; I' i FIG. 7 is a longitudinal vertical section through a further lifting apparatus with certain of its parts omitted for the sake of clarity, the section of FIG. 7 being taken in the direction of arrows as seen from the line VII-VII of FIG. 8;

FIG. 8 is a horizontal section as seen in the direction of arrows from the lineVIII-VHI of FIG .7; and

FIG. 9 is a schematic diagram of the electric and hydraulic circuitry in the'lifting apparatus of FIGS. 7 and 8..

Referring to the drawings, and first to FIGS. 1 and 2, there is shown a lifting apparatus which comprises a base provided with parallel ways 21, 22 having elongated

slots

23, 24, a vertically movable polygonal platform 25 whose underside is provided with two parallel ways 26 (only one shown) having elongated slots27, and two pairs of'pivotally connected

intersecting supporting arms

28,29 and 30, 31 which constitute the means formoving the" platform between'an upper end position and a lower The lower ends of the arms" 28, are" pivotally secured to the ways 21, 22 by pins 32 and the' end position.

upper end of each of the arms 29, His pivotally'secured to one of the ways 26 by a pin 33. The arms 30, 31are pivotally connected to each other by a pin 34, and a simila'r pinconnfects the

arms

28, 29 so that the two pins 34 are coaxial with each other. The same applies to the

pins

32 and 33. The lower ends of the

arms

29, 31 carry fri ctionv reducing

roller followers

35, 36 which extend through and beyond the

slots

23, 24, and the upper ends of the a'rms28, 30 carry roller followers 37 (only one shown)' as a jack including a cylinder 38 which is pivotally secured to a stationary bracket 39, a piston whose push rod 38a is pivotally secured to a crosshead 40 extending between the lower portions of the

arms

28, 30, and a flexible supply conduit 41 which connects the chamber of the cylinder 38 with the pressure side of a rotary hydraulic pump 42 driven by' an electric motor 43. The pump 42 draws hydraulic fluid from a source here shown as an oil tank 44. When the cylinder 38 receives hydraulic fluid through the conduit 41, its push rod 38a causes-the

followers

35, 36, 37 to travel in the

slots

23, 24, 27 toward the left-hand end'of the lifting apparatus, as viewed'in' 'FIG. 1 or 2, whereby the

arms

28, 29 and 30, 31 pivot with respect to each other and raise the platform 25;

The electric circuit of the motor 43 (see FIG. 3) in: cludes a starter switch 45, a source 46 of electrical energy, and a limit switch'47 which is connected in series with the switch and whose movable portion or trip 48: is located in the path of the roller follower 35 so as to open the circuit of the motor 43 and to' arrest the pump 42 when the platform 25 reaches a predetermined optimum upper level. The supply conduit 41 contains a one-way check valve 49, and a simple throttle valve 50 located downstream of the valve 49.

The lifting apparatus further embodies a safety device which prevents any damage to its component parts in the event that the limit switch 47 would fail to function pro perly and would permit the motor 43 to operate after the platform 25 .hasreached the optimum distance from the base ,20. This safety device includes a two-armed actuatiri'g lever 51 which is pivotable about a fixed pivot 52 and one section or arm of which extends into the path of the roller follower 36. The other section or arm of the lever Slis arranged to engage a movable portionhere shown as the stem 53 of a normally closed safety valve 54 which provided in a return conduit 55 communicating with the supply conduit 41 at a point upstream of ma hem valve 49 but downstream of the pump 42 and leading to the tank 44. Thus, when the limit switch 47 fails to arrest the motor 43, the actuating lever 51 opens the safety valve 54 and insures that any further pressure fluid deliveredby the pump 42 merely flows back to the tank 44; The check valve 49 insures that the fluid contained in the 7 cylinder 38 cannot flow back to the return conduit 55 so backto the tank 44. The valve'57 opens when the circuit of its solenoid is completed an'd'the weight of the platform 25 automatically expels pressure fluid from the cylinder 38 7 via

conduits

41, 58 back to the tank 44.

It goes Without saying that the actuatinglever 51 may be mounted in the path of the

follower

35 or 37 and that this lever may be actuated by an intermediate portion of a supporting arm or by any other movable part of the lifting apparatus, The distance covered by thefollower 35 after this follower engages the trip 48 but before the follower 36 engagesthe lever 51 is normally'very small, for example, about 10 mm. It is also possible (though less practical) to mount the safety valve 54 on a moving part of the lifting apparatus and to use a rigid actuating member which may be non-movably (but adjustably) fixed to the base 20. This would merely amount to a reversal of functions. I I

In the embodiment of FIGS. 1 to 3, the mountingof the hydraulic jack including the cylinder 38 and push rod 38a is such that a comparatively high pressure is necessary to move the platform 25 frornits lower end position and that a comparatively low pressure is needed' to thereupon advance the platform toward itsuplper end position. This will be readily understood since, and if the platform 25 moves downwardly toward the" base 20, the angle enclosed by the axis of the cylinder 38 and the longitudinal extension of the arm 30 (see FIG. 1') increasesand may approach 180 degrees at the time the' platform 25 reaches its lower end position. On the other hand, when the platform 25 assumes the position of FIG. 1, the angle between the axis of the cylinder 38 and the longitudinal extension of the arm 30 is much smaller so that, quite obviously, a lower pressure suffices to maintain the platform in motion toward its upper end position once the platform has covered-the initial portion of its path toward the upper end position of FIG. 1. For example, the pressure necessary to move the platform 25.from its lower end poistion (in which the

followers

35, 36 are. adjacent to the right-hand ends of

th e slots

23, 24 and in.which the followers 37 are adjacent to the right-handends of the slots 27) may" be in the range of 210 atmospheres absolute pressure but the pressure necessary to. advance the platform in the last third of its path toward the upper end position need not exceed atmospheres absolute pressure. Therefore, the customary pressure relief valve which is always provided in such types of hydraulic lifting'apparat-us must be adjusted to withstand pressures of up to 220 atmospheres absolute pressure which is excessive when the platform moves toward and is close to its upper end position. This customary pressure relief valve which is adjusted to withstand pressure of up to 220 atmospheres and to open at such pressures is shown at 59 and, if desired, may form a structural unit with so as to open and close in response to opening and closing ofthe solenoid valve 57. Thus, when the pressure in the cylinder 38 reaches or exceeds 220 atmospheres absolute pressure, the

valves

57, 59 open in a fully automatic way to permit return flow of pressure fluid through the conduit 58 and back to the tank 44 in order to avoid physical damage to a complete destruction of certain component parts of the lifting apparatus. However, such pressure (220 atmospheres absolute pressure) is often excessive and, therefore, another feature of the present invention resides in the provision of means for automatically switching from operation with the pressure relief valve 59 to operation with a prefera-bly adjustable second pressure relief valve 60 provided in a return conduit 61 which communicates with the supply conduit 41 and with the tank 44. This second pressure relief valve 60 is controlled by a valve 62 of conventional construction which is movable between a fully open and a fully closed position and which is normally closed. The control valve 62 com-prises a movable portion, here shown as a trip 63, which is located in the path of an actuating member 64 mounted on the arm 30 and preferably adjustable in the longitudinal direction of this arm so that it may open the control valve 62 in any of a number of selected positions of the platform 25. For example, the plate 65 of the actuating member 64 may be fixed in a series of positions longitudinally of the arm 30.

It is assumed that the second pressure relief valve 60 is adjusted (see the handle 60a) to open at a pressure of 150 atmospheres absolute pressure. When the platform 25 assumes its lower end position or moves away from its lower end position, the actuating member 64 is spaced from the trip 63 and the control valve 62 is closed so that the second pressure relief valve 60 is inactive. The hydraulic circuit of the lifting apparatus is then controlled by the first pressure relief valve 59 which is set to open in response to a pressure of 220 atmospheres absolute pressure. As the platform 25 continues to move in upward direction, the actuating member 64 engages the trip 63 and opens the control valve 62 so that the second pressure relief valve 60 is now compelled to resist the pressure prevailing in the supply conduit 41 upstream of the check valve 49 and to open if the pressure in this portion of the supply conduit exceeds 150 atmospheres absolute pressure. When the platform 25 remains in its upper end position, a pressure of 150 atmospheres suffices so that at least some component parts of the lifting apparatus are protected from any damage or breakage in the event that the pressure upon the platform 25 would exceed the pressure to which the relief valve 60' responds when the platform is moved to or approaches its upper end position. Thus, when the control valve 62 is open and the load upon the platform 25 is such that a pressure in excess of 150 atmospheres is necessary to raise the platform, the relief valve opens automatically and permits return flow of fluid from the pressure side of the pump 42 to the high and might result in damage to certain component parts of the lifting apparatus.

The purpose of the one-way check valve 49 is to avoid damage to the pump 42 in the event that pressure prevailing in the chamber of the cylinder 38 would fluctuate in response to changing loads upon the platform 25. The throttle valve 50 is of the customary type and may be adjusted by hand (see the handle 50a in FIG. 2) to insure that fluid contained in the cylinder 38 cannot return to the tank 44 at a very fast rate such as could cause the platform to strike against the base and to damage tank 44. On the other hand, when the operator closes the switch 56 in order to move the platform 25 to its lower end position, the actuating member 64 moves away from the trip 63 so that the control valve 62 closes in a fully automatic way (as soon as the platform reaches a predetermined inter-mediate position) to seal the valve 60 from the supply conduit 41. The pressure relief valve 59 takes over and enables the pump 42 to maintain in the cylinder 38 a pressure of up to 220 atmospheres absolute pressure when the platform 25 is again moved from its lower end position.

It goes without saying that the control valve 62 and the actuating member 64 may be mounted in another portion of the lifting apparatus as long as the valve 62 opens in response to a predetermined movement of the platform 25 from its lower end position. For example, the trip 63 may be biased by a spring which maintains the control valve 62 in closed position and the actuating member 64 may be replaced by a cable or cord which is connected to the platform 25 and which pivots the trip 63 in a direction to open the control valve as soon as the platfonrn reaches a predetermined intermediate position. This and many similar modifications will be readily understood by men skilled in the art without necessitating a separate illustration.

The two

pressure relief valves

59, 60 are connected in parallel so that the valve 59 remains active at all times and that the valves 60 is operative only when the I pressure to which the valve 59 responds is undesirably certain parts of the lifting apparatus when the switch 56 is closed.

FIGS. 1 and 2 show a portion of a housing 20a which forms part of or is secured to the base 20 and which accommodates the pump 42, the tank 44, the motor 43, the limit switch 47 and many other component parts of the lifting apparatus. The arrangement is preferably such that the apparatus forms a flat box-like structure whenever the platform 25 assumes its lower end position and comes close to or into actual abutment with the base 20.

FIG. 4 illustrates a slight modification of the just described lifting apparatus wherein a single pressure relief valve 59' is constructed in such a way that its resistance to pressure of hydraulic fluid varies in response to movement of the platform 25 between a lower and an upper end position. This valve 59' is of the known type wherein a rotary adjusting shaft 66 serves to change the bias of a spring or the like in order to regulate the 'valve in a sense that the valve will resist a higher pressure when the platform is in or near its lower end position and that the valve will resist a lesser pressure when the platform approaches or assumes its upper end position. The adjusting shaft 66 carries a pinion forming part of a gear train including

additional gears

68, 69, '70 the latter of which may be rotated by a lever 71 having a roller 72 extending into an elongated slot 73 of a modified supporting arm 30. When the arm 30 causes the lever 71 to pivot in a counterclockwise direction (i.e., when the 'arm 30' moves the platform to its upper end position), the resistance which the relief valve 59 offers to pressure in the conduit 41 decreases so that the valve 59 is a true presure relief valve which is always adjusted in such a way that it can resist pressures which exceed only slightly the maximum permissible pressure in a given position of the platform. For example, when the platform (carried by the arm 30 and by three additional arms in the same way as described in FIGS. 1 and 2) assumes its lower end position, the pump 42 might be called upon to deliver oil ,or another hydraulic fluid at a pressure of about 300 atmospheres absolute pressure in order to lift the platform and the articles supported thereon from such lower end position. On the other hand, when the platform constitutes a transmission connecting the pressure relief valve 59' with a movable component part of the lifting apparatus) will move the shaft 66 between two end positions in one of which the valve 59' may resist about 310 atmospheres and in another of which the valve 59' may resist about 210 atmospheres absolute pressure. Thus, the pressure at which the valve 59' opens to permit return flow 'of pressure fluid from the chamber of the cylinder 38 exceeds only slightly the maximum desirable pressure in the cylinder to make sure that all parts of the apparatus are satisfactorily protected in all positions of the platform 25. 1

The structure shown in FIG. 4

replacesthe valves

59, 60, 62, the return conduit 61, the trip 63, and the actuating member 64 of FIGS. 1 to 3. Its advantage is seen in that the resistance which the single pressure relief valve 59 offers to pressure varies automatically (i.e., not stepwise as in FIGS. 1 to 3) and that such resistance will loaded. regulating the rate of fluid return flow through the con- 7 I never be too high for a given position of the platform.

As a rule, the pressure necessary at the time the platform 25 is moved from its lower end position exceeds by about 50 percent that pressure which is. necessary when the platform approaches or assumes its upper end position. FIG. 4 does not show the throttle valve 50, the check valve 49 and certain other parts of the hydraulic circuit. The purpose of the gear train 67-70 is to respond to minimal changes in the angular position of the lever 71,- i.e., the gear train actually constitutes a stepup transmission which causes substantial angular displacements of the pressure-regulating shaft 66 in response to small angular diplacements of the lever 71 and arm 30.

FIG. illustrates the electric and hydraulic circuitry of a further lifting apparatus wherein the throttle valve 50 is replaced by a volume governor 74 having adjusting means 75 and serving to control with great accuracy the outflow of pressure fluid from the chamber of the cylinder 38 when the operator desires to return the platform (not shown in FIG. 5) to its lower end position. The electric circuitry of the modified apparatus comprises a time-lag relay 76 which receives impulses from the limit switch 47 and which serves to close the switch 56 after elapse of a predetermined period of time so that the platform may automatically return to its lower end position after it assumes its upper end position and after it remains in the upper end position for a period of time determined by the setting of the time-lag relay 76. Otherwise, the structure shown in FIG. 5 differentiates only in minor respects from the structure shown in FIGS. 1 to 3. It is to be noted that the

valve

57, 59 form a structural unit having a common housing 77.

An important advantage of the volume governor 74 is that the speed at which the platform descends to its lower end position may be regulated with utmost accuracy and with a tolerance of :3 percent. In other words, the speed at which the platform descends under its own weight is the same as if the platform is fully loaded and supports several tons of sheet metal, bars, rods, profiles or other types of load. The handle 75 serves to permit adjustments in such speed irrespective of whether the switch 56 is open or closed.

The apparatus of FIG. 5 operates as follows:

It is assumed that the platform has been moved to or near its upper end position and that the operator desires to return the platform to the lower end position by permitting fluid to escape from the cylinder 38. In the first step, the operator opens the switch 45 (if the platform did not reach entirely its upper end position) or awaits that the follower 35 (see FIGS. 2 and 3) opens the limit switch 47 by engaging the trip 48. This arrests the electric motor 43 so that the pump 42 ceases to deliver pressure fluid through the check valve 49 and to the cylinder 38. In the next step, the operator closes the switch 56 or awaits that this switch closes in a fully automatic way in response to energization of the time-lag relay 76 subsequent to opening of the limit switch 47. The switch 56 completes the circuit of the solenoid valve 57 and the

valves

57, 59 then permit pressurerfluid to flow through the return conduit 58' and back to the tank 44 at the rate determined by the setting of the volume governor 74.

in a narrow range normally not deviating by more than 3.

percent from an optimum value. This means that the platform descends at a speed which is not dependent on the load upon the platform because the speed is the same when the platform is empty or when the platform is fully A conventional throttle valve is incapable of duit 41 with anything resembling such accuracy, i.e., the greater the load the more rapid is the descent of the platform 25 in FIGS. 1 to 3 to its lower end position because the throttle valve 50 cannot regulate the rate of flow in the same way as the governor 74. This governor is actually a reducing valve which may be set in a number of positions in each of which it permits the hydraulic fluid to flow through the conduit 58 at a desiredspeed. It was found that, when the lifting apparatus is equipped with :a conventional throttle valve, the speed at which a fully loaded platform descends is a multiple of the speed of an empty platform. This is particularly undesirable when the descending platform is supposed to initiate several impulses serving to control one or more other machines which cooperate with the lifting apparatus. For example, the descending platform may start a machine which removes the load therefrom and which is supposed to be actuated at predetermined intervals which are entirely independent of the load upon the platform.

By adjusting the governor 74 with the handle 75 or in another suitable way, the operator changes the speed at which the platform descends but, once the governor 74 is adjusted it will maintain the speed of the descending platform constant until and unless the operator" decides to readjust the handle 75. If desired, the handle 75 may be coupled with a programming device78 which serves to automatically regulate the speed of the descending platform in. accordance with a predetermined schedule. Such programming devices are well known in the art and, therefore, the exact construction of the device 78 forms no part of this invention. ,Any programming device which is capable of automatically adjusting the governor '74 while the lifting apparatus is in actual use may be employed and, if desired, such programming device may be actuated by one of the arms 2831 (shown in FIGS. 1 and 2) or by theplatform itself so that it will automatically change the rate of speed at which the platform descends when the platform reachesone or more interfurther safety device which may be utilized with great advantage not only in the previously described embodiments of my improved lifting apparatus but also independently of the novel features which were described in connection with FIGS. 1 to 5. This safety device serves to prevent accidents resulting from placing a rigid object between the base and the platform at the time the platform descends toward its lower end position. Also, the safety device of FIG. 6 protects a workman who might have accidentally placed his foot onto the base while he operates the controls or supervises the operation of the lifting apparatus. Since such apparatus are often used to lift or lower substantial loads and since the platform and the base normally consist of rigid metallic material, the danger of serious injury is ever present, especially if the operator is inexperienced.

As shown in FIG. 6, the marginal portions at the underside of the platform 25 may be provided with a hollow body. 80 of elastically deformable rubber or synthetic plastic. This body preferably assumes the form of an elongated tube having a flat upper side which abuts against the underside of the platform 25. The tube 80 is secured to'the platform by means of

metallic strips

81, 82 or by "similar fasteners so that it cannot change its position with reference to the platform. The internal space 83 of this tube is filled with a fluid medium which also fills a flexible connecting pipe 84 leading to a pressure-responsive control element, here shown as an electric switch 85, connected in circuit with the solenoid valve 57, see FIG. 3. The switch 85 is normally closed and'opens only when the pressure prevailing in the space 83 rises in response todeformation of the tube 80. The

fluid contained in the pipe 84 may act against a diaphragm or a suitable plunger of the switch 85, and this switch is sufliciently sensitive to respond to a pressure difference of mm. water column or even less so as to make sure that the outflow of fluid from the cylinder 38 is arrested before the leg or the hand of a workman sustains serious damage if the workman happens to place one of his limbs into the path of the descending platform 25. Also, the switch 85 will open if a rigid object is placed onto the base 28 or extends into the path of the descending platform 25 so that the valve 57 closes before the inserted object may cause serious damage to the lifting apparatus.

The tube 80 need not always extend around the entire underside of the platform 25. For example, and if the platform is not accessible from one, two or three sides, such nonaccessible sides need not be provided with the safety device of FIG. 6. On the other hand, and as shown in FIG. 2 (see a portion of a second tube 86a), the safety device may also be provided on the base to make sure that further descent of the platform is prevented without delay not only when an object or a limb abuts against the underside of the platform but also when a leg is placed onto the base 20. Thus, and since the weight of the platform is substantial, serious damage or injury could occur even if the switch 85 would prevent outflow of fluid from the cylinder 38 Very shortly after the pressure prevailing in the space 83 of the tube 80 rises by 5 mm. water column or by a similar value. If the base 20 is also provided with a tube 80a, the danger of injury or damage is very remote. The flexible pipe 84 may be led along one of the legs (e.g., along the leg 31 shown in FIG. 1) and may be secured thereto by suitable clamps 86 or the like. This is necessary whenever the electric circuitry of the solenoid valve 57 is accommodated in the base 20.

The safety device of FIG. 6 is a low-cost structure which may be readily installed in many existing lifting apparatus and which always acts upon the mechanism which serves to control or to initiate the descent of platform to its lower end position. This applies with equal force to lifting apparatus wherein the platform is lifted and lowered by mechanical and/ or electrical means and regardless of whether the safety device is mounted on the base and/or on the platform.

Actual tests with the device of FIG. 6 have shown that fluid contained in the space 83 of the tube will operate the switch with no delay even if it has become partially damaged as long as the fluid entrapped in the space 83 remains sealed from the atmosphere. Switches which respond to small changes in pressure are well known in the art; therefore, the switch 85 by itself forms no part of the present invention.

FIGS. 7 to 9 illustrate a further lifting apparatus which constitutes a modification and simplification of the previously described lifting apparatus. The base is provided with parallel ways 121, 122 for

roller followers

135, 136 at the lower right-hand ends of the supporting arms 129, 131. This base also carries two brackets 120c, 120d which are provided at its left-hand end and which carry pivot pins 132 for the lower ends of supporting

arms

128, 130. The upper ends of the arms 129, 131 carry pivotpins 133 which are secured to the platform 125, and the upper ends of arms 128, carry roller followers 137 which are received in U- shapcd ways 126 provided at the underside of the platform 125. The safety device for the platform 125 com-- The supply conduit 141 which is connected with the cylinder 138 and with the pressure side of the pump 142 accommodates a check valve 149 which prevents return flow of fluid to the pump and a simple throttle valve 150 which is an optional feature of the lifting apparatus because the hydraulic circuit of this apparatus also comprises a volume governor 174 corresponding to the governor 74 of FIG. 5 and mounted in a return conduit 158 branching from the supply conduit 141 at a point between the

valves

149, 150 and leading to the tank 144. This return conduit 158 contains the solenoid valve 157 and the main pressure relief valve 159. A second or auxiliary pressure relief valve 160 is mounted in a second return conduit 161 which leads to the tank 144 and which branches from the supply conduit 141 at a point upstream of the check valve 149. The conduit 161 also contains a specially constructed two-way control safety valve 162 which may permit fluid through the conduit 161 and toward the pressure relief valve 168 and/ or through a third return conduit 155 leading back to the tank 144.

The push rod 133a of the cylinder 138 is articulately connected with a crosshead 141 which connects the lower portions of the supporting arms 129, 131 at a point beneath the pivot pin 134. If desired, the push rod 13811 of the cylinder 138 may be coupled to the underside of the platform 125 by utilizing a two-armed lever or the like.

The electric motor 143 of the pump 142 is connected in circuit with a source 146 of electrical energy, with a manually operable starter switch 145, and with a limit switch 147 whose trip 148 may be actuated by the follower 136 (see FIG. 8) in the same way as described in connection with FIGS. l-3. When the limit switch 147 fails to open the circuit of the motor 143 even though the platform 125 has reached the desired maximum distance from the base 120, the roller follower engages a two-armed actuating lever 151 which is pivotable about a vertical pin 152 and whose upper arm (as viewed in FIG. 2) may shift a spring-biased opener or stem 163 of the combined control and safety valve 162 whereby the latter permits return flow of pressure fluid from the supply conduit 141 via conduit 155.

The valve 162 further comprises a second opener, here shown as a trip 163a, which is located in the path of a cam-shaped actuating member 164 carried by the supporting arm 131 or by the crosshead and serving to open a second passage in the valve 162 so as to permit flow of pressure fluid toward the second pressure relief valve 160. The positioning of the actuating member 164 is preferably such that the trip 163a is actuated at the time the platform 125 moves from its lower end position and is approximately midway between its end positions. This means that the second pressure relief valve 160 (which can open in response to a pressure substantially lower than the pressure necessary to open the relief valve 159) will become active while the platform 125 moves toward and remains in its upper end position. The actuating member 164 travels in :an arcuate path which is determined by pivotal movement of the crosshead 148 about the pin 134 and by simultaneous movement of the crosshead toward or away from the base 121 The position of the actuating member 164 may be adjusted in the same way as that of the member 64.

Otherwise, the operation of this lifting apparatus is exactly the same as that of the apparatus described in connection with FIGS. 1 to 6. The switch is closed by hand or by remote control if the operator desires .to move the platform 125 from its lower end position whereby the motor 143 rotates the pump 142 and the latter draws pressure fluid from the tank 144 to deliver such fluid through the supply conduit 141 via valves 149, and into the chamber of the cylinder 138 which causes the piston rod 138a to move the

arms

128, 129 and 130, 131 so as to pivot about the respective pins 134 and to move the platform upwardly and away from the base 129. If the limit switch 147 fails to respond 1 1 when the platform 125 reaches the desired optimum distance from the base, the lever 151 is rocked in a clockwise direction (as viewed in FIG. 8) and causes the valve 162 to provide a passage between the

conduits

141, 155 whereby any further fluid delivered by the pump 142 merely flows back to the tank 144.

If the operator thereupon desires to return the platform 125 to its lower end position, he closes the switch 156 to complete the circuit of the solenoid valve 157 which opens the pressure relief valve 159 so that fluid contained in the cylinder 133 may flow back to the tank 144 via throttle valve 150, volume governor 174, valves 157, 159, and conduit 158.

The adjustments in the position of the trip 163a in response to upward movement of the actuating member 164 may be gradual so that the valve 162 open a path for return flow of pressure fluid to the second relief valve 160 after elapse of a given period of time.

The pressure-responsive switch 185 will open the circuit of the solenoid valve 157 when the fluid contained in the space 183 of the tube 189 undergoes compression'resulting from placing of a solid object into the path of the descending platform. The valves 157, 159 then close automatically and prevent further outflow of fluid from the cylinder 138.

Without further analysis, the foregoing will so fully 7 reveal the gist of the prcsent invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and'specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is: V

1. A hydraulic lifting apparatus comprising a base; a plurality of moving parts including a platform located above and movable toward and away from said base, and supporting means operatively connected with said base and with said platform and arranged to move the platform between an upper and a lower end position; operating means arranged to move said supporting means and including a source of hydraulic fluid, a hydraulic lifting device, a supply conduit connecting said source with said lifting device, and pump means mounted in said supply conduit to deliver fluid to said lifting device whereby the latter acts upon one of said moving part and moves the platform to said upper end position; a first return conduit connected with said supply conduit downstream of said pump means and arranged to return pressure fluid to said source; a normally closed multiway valve in said return conduit; 21 second return conduit connecting said multiway valve with said source; a first movable opener operatively connected with and arranged to open in said multiway valve a passage for the flow of pressure fluid from said first return conduit to said second return conduit in response to movement thereof; a second movable turn conduit in response to movement thereof; a pressure relief valve mounted in said first return conduit downstream of said multiway valve; first actuating means connected with one of said movable parts and arranged to move said second opener in response to movement of said platform to an intermediate position between said end positions so that said second opener permits the flow of fluid to said pressure relief valve when the pump means is in operation; and second actuating means connected withone of said moving parts and arranged to move said first opener when the platform at least approaches said upper end position so that said multiway valve permits any additional fluid delivered by said pump means to flow through said second return conduit and back to said source.

2. A hydraulic lifting apparatus comprising a base; a plurality of moving parts including a platform located above and movable toward and away from said base, and supporting means operatively connected with said base and with said platform and arranged to move the platform between an upper and a lower end position; operating means arranged to move said supporting means and including a source of hydraulic fluid, a hydraulic lifting device, a supply conduit connecting said source with said lifting device, a pump provided in said supply conduit and rranged to deliver fluid to said lifting device so that the latter acts upon one of said moving parts and moves the platform to said upper end position, an electric motor arranged to drive said pump, a starter switch and a source of electrical energy connected in circuit with said motor, and a normally closed limit switch connected in series with said starter switch and having a movable portion adapted to open said limit switch in response to movement thereof, said movable portion being located in the path of one of said moving parts to open said limit switch and to arrest said pump when the platform reaches a predetermined distance from said base close to said upper end position thereof; and a safety device including a return conduit communicating with said supply conduit downstream of said pump and leading to said source of hydraulic fluid, and a normally closed safety valve provided in said return conduit and arranged to open in response to movement of said platform beyond said predetermined distance from said base so that any additional fluid delivered to said pump returns to said source whenever a moving part engages the movable portion of said limit switch and the latter fails to open the circuit of said motor.

3. A hydraulic lifting apparatus comprising 'a base member; a plurality of moving parts including a platform member located above and movable toward and away from said base member, and supporting means operatively connected with said members and arranged to move the platform member between an upper and lower end position; operating means arranged to move said supporting means and including a source of hydraulic fluid, a hydraulic lifting device, a supply conduit connecting said source with said lifting device, and pump means mounted in said supply conduit andarranged to deliver fluid to said lifting device so that the latter engages one of said moving parts and moves the platform member to said upper end position; means for facilitating movement of said platform member to said lower end position including a return conduit communicating with said source and with said supply conduit at a point downstream of said pump means and a valve provided in said return conduit for controlling the flow of fluid from said lifting device; and a safety device including a body of elastically deformable material secured to at least one of said members so as to face the other member, said body defining a fluid-filled internal space, and a pressuresensitive control element arranged to close said valve in response to change in pressure of fluid in said internal space whereby the outflow of fluid from said lifting device is terminated automatically if a foreign object exerts a deforming pressure upon said fluid-filled body.

4. A lifting apparatus as set forth in claim 3, wherein said valve is a normally closed solenoid valve and wherein said control element is a normally closed pressuresensitive electric switch connected in circuit with said solenoid valve, the circuit of said valve further comprising a releasing switch which is closed at the will of the .a plurality of marginal portions and wherein said fluid- 13 filled body is an elongated tube secured to the underside and extending along at least one marginal portion of said platform member.

7. A lifting apparatus as set forth in claim 4, wherein said safety device further comprises a flexible pipe connecting said fluid-filled body with said pressure-sensitive switch, said pipe being secured to and being movable with said supporting means.

8. A lifting apparatus as set forth in claim 4, wherein said base member is of polygonal shape having a plurality of marginal portions and wherein'said fluid-filled body is an elongated tube secured to the upper side and extending along at least one marginal portion of said base member.

9. A hydraulic lifting apparatus comprising a base member; a plurality of moving parts including a-platform member located above and movable toward and away from said base member, and supporting means operatively connected with said members and arranged to move the platform member between an upper and lower end position; operating means arranged to move said supporting means and including a source of hydraulic fluid, a hydraulic lifting device arranged to operate at higher pressure when said platform member is nearer to said base member and at lower pressure when said platform member is more distant from said base member, a supply conduit connecting said source with said lifting device, and pump means mounted in said supply conduit and arranged to deliver fluid to said lifting device so that the latter engages one of said moving parts and moves the platform member to said upper end position; a return conduit communicating with said source and with said supply conduit at a point downstream of said pump means; an adjustable pressure relief valve provided in said return conduit and including an adjusting element; and transmission means for actuating said adjusting element in response to movement of said platform member with respect to said base member so that the resistance which said valve offers to flow of fluid through said return conduit decreases when the platform member moves away from the base member.

10. A lifting apparatus as set forth in claim 9, wherein said adjusting element is a rotary shaft and wherein said transmission means comprises a gear train arranged to rotate said shaft and a lever operatively connected with said gear train and with one of said moving parts to rotate said shaft through said gear train in a response to movement of said platform member.

11. A lifting apparatus as set forth in claim 9, wherein said transmission means is a stepup transmission.

12. A hydraulic lifting apparatus comprising a base; a plurality of moving parts including a platform located above and movable toward and away from said base, and supporting means operatively connected with said platform and with said base and arranged to move said platform between an upper and a lower end position; operating means arranged to move said supporting means and including a source of hydraulic fluid, a hydraulic lifting device, a supply conduit connecting said source with said lifting device, and pump means mounted in said supply conduit and arranged to deliver fluid to said lifting device whereby the latter acts upon one of said moving parts and moves the platform to said upper end position; a return conduit communicating with said source and with said lifting device; an adjustable volume governor provided in said return conduit and arranged to regulate return flow of fluid from said lifting device when said platform moves toward its lower end position; and a programming device operatively connected with and arranged to adjust said volume governor in accordance with a predetermined schedule.

13. A lifting apparatus comprising a base member having an upper side; a platform member having an underside and being located above said base member; first operating means for moving said platform member away 14 from said base member; second operating means for facilitating movement of said platform member toward said base member; and a safety device including a body of elastically deformable material secured to at least one of said members so as to facce the other member, said body defining a fluid-filled internal space, and a pressuresensitive control element arranged to inactivate said second operating means in response to changes in pressure of fluid'in said interval space whereby said platform member is held against movement toward said base member when a foreign object exerts a deforming pressure upon said fluid-filled body.

' 14. A hydraulic lifting apparatus comprising a base; a plurality of moving parts including a platform movable downwardly toward and upwardly away from said base, and supporting means operatively connected with said platform and with said base and arranged to move the platform between an upper and a lower end position; operating means arranged to move said supporting means and including a source of hydraulic fluid, a hydraulic lifting device, a supply conduit connecting said source with said lifting device, and pump means mounted in said conduit and arranged to deliver fluid to said lifting device whereby the latter acts upon one of said moving parts and moves the platform to said upper end position, said lifting device being arranged to operate at higher pressure when the platform is close to said lower end position and at lesser pressure when the platform is close to said upper end position; a first and a second return conduit each communicating with said source and with said supply conduit at a point downstream of said pump means; a first pressure relief valve provided in said first return conduit and arranged to open at a first predetermined pressure exceeding said higher pressure so as to permit return flow of fluid from said lifting device in response to said predetermined pressure; a second pressure relief valve provided in said second return conduit and arranged to open at a second predetermined pressure exceeding said lesser pressure but less than said higher pressure; and a normally closed control valve provided in said second return conduit upstream of said second pressure relief valve, said control valve having a movable portion located in the path of one of said moving parts and arranged to open said control valve in response to engagement by said last mentioned moving part when the platform moves away from said lower end position and reaches a predetermined level above said base.

15. A hydraulic lifting appparatus comprising a base; a platform located above and movable toward and away from said base; supporting means including at least one pair of pivotally connected intersecting supporting arms, one of said arms having a lower portion pivotally connected with said base and an upper portion guided by the platform and the other of said arms having a lower portion guided by said base and an upper portion pivotally connected with said platform above the lower portion of said one arm; a hydraulic jack having a cylinder pivotally secured to said base and a reciprocable push rod articulately connected to said supporting means in such a way that the platform is caused to move between an upper and a lower 'end position in response to reciprocation of said push rod; a source of hydraulic fluid provided in said base; a supply conduit connecting said source with said cylinder; a motor-driven pump provided in said supply conduit and arranged to deliver pressure fluid to said cylinder so as to move said platform to its upper end position; a return conduit communicating with said source and with said supply conduit at a point downstream of said pump; a normally closed safety valve provided in said reutrn conduit; means responsive to movement of said platform to a predetermined distance away from said base for automatically opening said safety valve so that any further fluid delivered by said pump when the platform reaches said predetermined distance flows through said safety valve and back to the source; a second return conduit communicating with said source and with said said second return conduit to permit return flow of fluid from said cylinder with resultant descent of the platform at the will of the operator.

16. A hydraulic lifting apparatus comprising a base; a plurality of moving parts including a platform located above and movable toward and away from said base, and supporting means operatively connected with said platform and with said base and arranged to move said platform between an upper and a lower end position; operating means arranged to move said supporting means and including a source of hydraulic fluid, a hydraulic lifting device, a supply conduit connecting said source withsaid lifting device, and pump means mounted in said supply conduit and arranged to deliver fluid to said lifting device whereby the latter acts upon one of said moving parts and moves the platform to said upper end position; a returnconduit communicating with said source and with said 16- li fting device; an adjustable volume governor provided in said return conduit and arranged to regulate return flow of fluid from said lifting device when said'platform moves toward. its lower'end positioma pressure relief, valve provided in said return conduit; and'a normally closed valve arranged to open simultaneously with said pressure relief. valve so. as to permit return flow of fluid from said lifting device via said volume governor.

I References Citedby the Examiner" UNITED STATES PATENTS ,1

5/1960 Fritz 187 -18" 5/1963. Black et al. 214 512-- WILLIAM FELDMAN, Primary Examinerr MILTON S, MEHR Exaf1 tiner. 7 W. SIMPSON, Assistqnt Examiner.

Claims

1. A HYDRAULIC LIFTING APPARATUS COMPRISING A BASE; A PLURALITY OF MOVING PARTS INCLUDING A PLATFORM LOCATED ABOVE AND MOVABLE TOWARD AND AWAY FROM SAID BASE, AND SUPPORTING MEANS OPERATIVELY CONNECTED WITH SAID BASE AND WITH SAID PLATFORM AND ARRANGED TO MOVE THE PLATFORM BETWEEN AN UPPER AND A LOWER END POSITIONS; OPERATING MEANS ARRANGED TO MOVE SAID SUPPORTING MEANS AND INCLUDING A SOURCE OF HYDRAULIC FLUID, A HYDRAULIC LIFTING DEVICE, A SUPPLY CONDUIT CONNECTING SAID SOURCE WITH SAID LIFTING DEVICE, AND PUMP MEANS MOUNTED IN SAID SUPPLY CONDUIT TO DELIVER FLUID TO SAID LIFTING DEVICE WHEREBY THE LATTER ACTS UPON ONE OF SAID MOVING PARTS AND MOVES THE PLATFORM TO SAID UPPER END POSITION; A FIRST RETURN CONDUIT CONNECTED WITH SAID SUPPLY CONDUIT DOWNSTREAM OF SAID PUMP MEANS AND ARRANGED TO RETURN PRESSURE FLUID TO SAID SOURCE; A NORMALLY CLOSED MULTIWAY VALVE IN SAID RETURN CONDUIT; A SECOND RETURN CONDUIT CONNECTING SAID MULITWAY VALVE WITH SAID SOURCE; A FIRST MOVABLE OPENER OPERATIVELY CONNECTED WITH AND ARRANGED TO OPEN IN SAID MULTIWAY VALVE A PASSAGE FOR THE FLOW OF PRESSURE FLUID FROM SAID FIRST RETURN CONDUIT TO SAID SECOND RETURN CONDUIT IN RESPONSE TO MOVEMENT THEREOF: A SECOND MOVABLE OPENER OPERATIVELY CONNECTED WITH SAID MULTIWAY VALVE AND ARRANGED TO PERMIT FLOW OF FLUID THROUGH SAID FIRST RETURN CONDUIT IN RESPONSE TO MOVEMENT THEREOF; A PRESSURE RELIEF VALVE MOUNTED IN SAID FIRST RETURN CONDUIT DOWNSTREAM OF SAID MULTIWAY VALVE FIRST ACTUATING MEANS CONNECTED WITH ONE OF SAID MOVABLE PARTS AND ARRANGED TO MOVE SAID SECOND OPENER IN RESPONSE TO MOVEMENT OF SAID PLATFORM TO AN INTERMEDIATE POSITION BETWEEN SAID END POSITIONS SO THAT SAID SECOND OPENER PERMITS THE FLOW OF FLUID TO SAID PRESSURE RELIEF VALVE WHEN THE PUMP MEANS IS IN OPERATION; AND SECOND ACTUATING MEANS CONNECTED WITH ONE OF SAID MOVING PARTS AND ARRANGED TO MOVE SAID FIRST OPENER WHEN THE PLATFORM AT LEAST APPROACHES SAID UPPER END POSITION SO THAT SAID MULTIWAY VALVE PERMITS ANY ADDITIONAL FLUID DELIVERED BY SAID PUMP MEANS TO FLOW THROUGH SAID SECOND RETURN CONDUIT AND BACK TO SAID SOURCE.