US2945606A - Centering and clamping device - Google Patents

Description

3 Sheets-Sheet 1 A. Mus'scHooT ETAL CENTERING AND CLAMPING DEVICE July 19, 1960 EiledAug. 5. l1958 July 19, 1960 A, MUSSCHQQT E rAL 2,945,606

CENTERING AND CLAMPING DEVICE 5 Sheets-Sheet 2 Filed Aug. 5. 1958 Q r du 5 Sheets-Sheet 3 A. MUSSCHOOT ETAL CENTERING AND CLAMPING DEVICE July 19, 1960 Filed Aug. 5, 1958 United States CENTERING AND CLAMPING DEVICE Filed Aug. 5, 1958, Ser. No. 753,345

6 Claims. (Cl. 214-53) This invention relates to vibratory platforms for unloading free flowing solid material in bulk, such as gram or Ithe like, from railway box cars, and more particularly to apparatus for centering and clamping a box car upon the platform during the unloading operation.

Box car unloaders of the type with which the invention is concerned include a platform which is supported above a fixed base by rocker arm assemblies located near each end of the platform. The upper surface of the platform is provided with rails, one of which is located at an elevation above the other to tilt a box car supported upon the rails for gravitational discharge of a portion of the car load through a side door opening toward an underground receiving hopper. A rotating counterweight drive assembly is mounted upon and centrally between the pposite ends of the platform to drive the platform in oscillating movement which is constrained by the rocker arm assemblies into a controlled path rocking motion in which opposite ends of the box car are alternately elevated. The action ofthe drive assembly is assisted by spring groups mounted near each end of the platform.

In view of the nature of the motion imparted to the platform during the unloading operation, some structure is required which will hold the car stationary upon the platform during such operation. Further, because of the substantial mass presented by a fully loaded box car, it is highly desirable that the car, when moved onto the platform, be accurately, centrally located relative to the length of the latter in order that the most eicient driving motion may be applied to the car.

Accordingly, it is a primary object of the invention to provide a structure for automatically centering a box car upon a platform of the type described above and for firmly clamping the box `car to maintain it in such position during vibratorymovements of the platform.

Another object of the invention is to provide a car centering and clamping device having a substantial range of clamp movement combined with means for exerting a high clamping pressure.

Other objects and advantages of the invention will become apparent by reference to the following rspecification taken in conjunction with the accompanying drawings. l

In the drawings:

Figure 1 is a side elevational view of a box car unloader embodying the present invention;

Figure '2 is a schematic diagram of the hydraulic control system of the present invention; and

Figure 3 is a schematic diagram of the electrical control circuit employed in Combination with the hydraulic control system of Fig. 2. Y

In Fig. l, a box car 1.0 is shown supported upon a specially designed unloader 12 which is disposed within n pit 14 extending between two sections 16-16 of a railway track. The unloader 12 includes a platform 18 having a pair of rails 20 and 22 mounted upon its upper surface which define a continuation of the track sections 16--16. The rail 22l is supported at an elevation above i arent the rail 2.0 in order to produce a sidewise tilt to the car 10 when the latter is supported upon the platform 18. The corresponding tracks of the rail sections 16-16 are slightly elevated as shown in Fig. l in order to provide a smooth transition of the car between the platform and the track sections 16-l6.

The platform 18 is supported from two fixed bases 24 by means of rocker arm assemblies 26 which are each pivoted at one end to a base 24, as at 28, and pivotally coupled at its opposite end 30 to the lower surface of the platform 18. In addition to the rocker arm assemblies 26, each of the bases 24 includes a spring group 32 .disposed between the platform 18 and base. A ixed buer 3d on each base 24 is engageable with an associated buffer element 36 upon the platform 18 to limit the movement imparted to the platform.

The platform is driven in an oscillating rocking movement by a double shafted rotating counterweight drive 38 which is mounted upon the lower surface of the platform 18. 'Ihe action of the drive assembly 28 is such -that an oscillating horizontal force is applied longitudinally of the platform 18. The horizontally applied force is converted by the constrainment of-the rocker arms 26 to la rocking motion of the platform 18 wherein opposite ends of the platform are alternately elevated.

A pair of opposed end clamp assemblies 40a and 4,0 bl are mounted upon the platform 18, one adjacent each of the opposite ends of the platform. The end clamp assemblies etla and 40h each include the same components, the only difference being that they are oppositely disposed with respect to each other. Therefore, only the end clamp assembly 40a will be described 'in detail, it being understood that the description is equally'applicable to the clamp assembly 4Gb.

'I'he clamp assembly 40a includes a clamp member 42a which is mounted for movement between a retracted position, indicated in broken lines in Fig. 1, and a car engaging position, shown in full line in Fig. 1. The clamp member 42a is guided in its movement by a cam track 44a which is traversed by rollers l46a lmounted upon the clamp member.

The clamp member 42a is driven in its movement between its retracted and car engaging positions by means of a hydraulic motor 48a which includes a motor cylinder 50a mounted upon the platform 18. The cylinder 50a has a piston mounted therein for reciprocating move,- ment. The piston is coupled to the end clamp member 42a by a projecting piston rod 52a which is pivotally coupled at 54a to the clamp member 42a. The vpiston is driven within the cylinder 50a by conducting fluid under pressure to and from the respective ends of the cylinder by means of the hydraulic control circuit disclosed in Fig. 2. This circuit will be described in detail below. The exactly similar, but oppositely disposed, clamp as: sembly 401) is located at the opposite end of the platform 18, the analogous parts being indicated by similar refer.- ence numerals with b added thereto.

In order to prevent undesired movement ofthe platform 18 during the periods when a car is being moved on or off thereof, a lock assembly is located at each end of the platform. Again, each of the platform lock assemblies is identical and a description of one is equally applicable to the other. At the end of the platform upon which the end clamp assembly 40a is mounted, the lock assembly includes a conventional hydraulic motor 56a mounted upon the floor of the pit 14. The piston of themotor 56a is Ycoupled by its piston rod 58a to a bell crank 60a which in turn is pivot-ally coupled to a rod 62a engage-A able with a pad 64a mounted upon the bottom of the platform. A.

When the piston rod 58a is fully extended, as `.Shown in Fig. l, the rod 62a is driven upwardly into engagement with the pad 64a, thus preventing this end of the platform from moving below a position where the rails 20 and 22 of the platform 18 are in alignment with the adjacent track sections 16-16. When the motor 56a is actuated to retract the rod 58a into the cylinder, the bell crank 60a is rotated to lower the rod 62a downwardly away fromrthe platform, thus permitting oscillating movement of the platform to perform the unloading operation. An identical platform lock assembly is indicated at the opposite end of the platform, the subscript .b being employed with the analogous reference numerals.

, The hydraulic control system for actuating the end clamp operating motors 48a and 48b and the platform lock motors 56a and 56b is shown in Fig. 2 in the drawings. The source of pressure iiuid for operating the respective motors includes a pair of low pressure positive displacement pumps 64a and 64b and a pair of high pressure positive displacement pumps 66a and 66b. The pumps 64a and 64b may each take the form of a conventional reversible gear-type pump capable of furnishing a constant volumetric ilow of uid up to pressures of approximately 500 pounds per square inch. `For details of a suitable pump of this type, reference is made to Bulletin No. 139A of the Hydreco Division of the New York Air Brake Company. The high pressure pumps 66a and 66b preferably may each take the form of a conventional rotating vane, constant delivery-type pump such as those described in Bulletin No. DP300A of the Kalamazoo Division of the New York Air-Brake Company.

The low pressure pumps 64a and 64b are both driven from a single reversible electric motor 68, while both of the high pressure pumps 66a and 66b are driven from another electric motor 70. The end clamp motor 48a and platformlock motor 56a at one end of the platform 18 are both connected to the low pressure pump 64a and the high pressure pump 66a, by suitable hydraulic connections.

The following description of the hydraulic connections between the pumps 64a and 66a and the clamp and locking motors 48a and 56a is equally applicable to the connections between the pumps 64b and 66b and the clamp and locking motors 48b and 56h. The low pressure pump 64a is connected to its associated end clamp motor and platform lock motor by means of a pair of conduits 72a and 74a leading from opposite sides of the pump 64a. Since the pump 64aris reversible, either of the conduits 72a and 74a may function as an inlet or outlet conduit for the pump 64a, depending upon the direction in which the pump is driven.

The conduit 72a is connected directly into the head end of the end clamp operating motor 48a by means of a branch conduit 76a. The head end of the cylinder 56a of the platform lock operating motor is connected to the conduit 72a lby means of a conduit 78a which has a pilot operated check valve 80a connected therein. The rod end of the platform lock motor is connected to the conduit 74a by means of conduits 81a and 82a, the conduit 81a being one branch of the conduit 82a, whose other branch 84a is connected to the rod end of the end clamp operating motor 48a through a flow regulating valve 86a having a pair of parallel branch passages. One of the passages within the valve 86a is restricted to pass a controlled ow of fluid in either direction, while the other branch passage of the valve 86a includes a one-way check valve oriented to permit ow of fluid through the valve 86a only in the direction toward the cylinder 50a.

The conduit 82a is connected to the Vconduit 74a through a second pilot operated check valve 88a. The pilot pressure for operating the valve 88a is obtained from the conduit 72a by means of the control conduit 90a. Each of the conduits 72a and 74a is provided with a pressure release valve 92a and 94a respectively for fventing the conduits to a sump or reservoir R in the event that pressure within either of the conduits builds up to a value of approximately 500 p.s.i. The conduit 72a may also be connected to the sump or reservoir R through a hydraulically operated two-way valve 96a which is connected in a conduit 98a extending between the conduit 72a and the conduit 74a. The conduit 98a is connected to the sump R through a branch conduit 100a. Flow of pressure uid from the conduit 74a to the conduit 190e is prevented by means of a one-way check valve 102a connected in the conduit 98a between the respective conduits 74a and 10011.

The hydraulically piloted valve 96a is movable between two positions, one of which permits the flow of fluid from the conduit 72a through the valve to the conduit 10041 and the other of which prevents the flow of fluid from the conduit 72a. The valve is moved to the first mentioned position-to permit ow of fluid through the conduit 98a-when pressure is applied'to the conduit 74a. The pressure in conduit 74a is applied to one hydraulic operator 104a of the valve 96a through a conduit 106g. Control pressure to move the valve 96a to its other position is applied to the other hydraulic operator 108a by means of a conduit 110a which is connected to the conduit 90a and thus to the conduit 72a.

Since pressure fluid from the high pressure pump 66a is employed in the clamp and locking motors only when the respective piston rods are moved to their retracted positions, the pump 66a is coupled directly to the conduit 82a by a conduit 112a which is connected to the end of the conduit 82a between the pilot operated check valve 88a and the respective clamp and locking motors. A pressure release valve 114a is connected into the conduit 112a to vent conduit 112a to the reservoir R whenever the pressure within the line 112a exceeds 1600 p.s.i Fluid is supplied to the inlet side of the pump 66a from the sump or reservoir R by means of a conduit 116.

In addition to the various valves for controlling the flow of lluid, pressure operated electrical switches 118a and 120a are tapped into the hydraulic circuit to control the energization of the respective pump operating motors 68 and 70. The pressure switch 118a is connected by means of a conduit 122e to the conduit 90a and hence to the conduit 72a on one side of the low pressure pump 64a while the pressure switch 120e is connected, by means of a conduit 124:1 directly to the high pressure conduit 112a.

The electrical circuit for controlling the operation of the pump driving motors 68 and 70 and the motor 38M of the platform oscillating drive 38 is shown in Fig. 3 of the drawings. Each of the aforementioned motors is energized from a 220 volt three-phase alternating current supply L1, L2 and L3. The various electrical contacts and control relays are coupled to receive a volt supply from the lines L2 and L3 as at 130.

It is believed that the electrical control circuit may be more clearly described by setting forth the functions of the various relays and contacts in terms of operation of the clamping and centering device, and hence the description of the electrical control circuit and the description of the operation will be combined.

As initial conditions, it will be assumed that the end clamp assemblies 40a and 4Gb have been located in their retracted positions, the platform lock assemblies are extended to their platform locking positions, the oscillating drive 38 is stopped, and a car 10 has been moved onto the platform 18 to a position approximately symmetrical with respect to the ends of the platform. At this time, all of the various manually actuated switches are located in the positions shown in Fig. 3.

.The first step in operating the device is to move the end clamp assemblies 40a-and 40b upwardly into engagement with the car 10 to center the car with respect to the platform and to clamp it in its centered position. This operation is commenced by manually closing a clamps up switch 132'. Closing of the switch 132 55 completes a circuit v'across the 110 volt supply lines 134 and 136 through a relay R1. Energization of the relay Ril closes contacts Rla to complete a circuit across the lines 134 and 136 through the contacts Rla, normallyv closed contacts Da and the high pressure pump drive motor control relay MB. Simultaneously with the closing of the contacts Rla, contacts Rlb are closed, thereby completing a second circuit across the supply lines 134 and 136 through the contacts Rla, Rlb, a second normally closed contact Db and the clamps up control relay U. Each of the control relays MB and U then close their respective lock in contacts MBa and Ua. Once the lock in contacts MBa and Ua are closed, the up button 132 may be released, and the control relays MB and U will remain energized.

In addition to its lock in contacts MBa, the control relay MB closes contacts MBb, MBc and MBd to connect the high pressure pump drive motor 70 to the respective 220 volt supply lines L1, L2 and L3. Energization of the clamps up relay U closes contacts Ub, Uc and Ud, thereby connecting the low pressure pump drive motor 68 to the supply lines L1, L2 and L3 to energize the motor 68 to drive in a direction which causes the pumps 64a and 64b to pump Huid under pressure to the rod ends of the respective motors 48a and 48h. Fluid from the pump 64a passes through the line 74a, valve 88a and conduit 82a into the rod ends of the end clamp motors 48a and platform lock cylinder 56a. Similar ow occurs from the pump 64b through line 74h, valve 88h and conduit B2b. Since the high pressure pump driving motor 70 operates in only a single direction, its energization likewise causes the pumps 66a and 66h to pump fluid from the pumps through the conduits 112a and 112b and hence into the conduits 82a and 82b to assist the low pressure pumps in supplying iluid to the rod ends of the respective end clamp and platform lock motors. Since the ow of uid through the respective circuits connected to the pumps 64a and 66a and 64b and 66h is the same, the operation of the circuit containing pumps 64a and 66a will be set forth, with the understanding that the Same action occurs simultaneously in the circuit containing the pumps 64b and 66h.

As the respective piston rods are retracted toward the head end of their respective cylinders, fluid flows from the head ends of the cylinders into the conduit 72a. Fluid from the head end of the end clamp operating motor 48a flows directly into the conduit 72a by means of the conduit 76a. Fluid from the head end of the platform lock motor, however, must pass through the pilot operated check valve 80a. This valve is unseated by pressure iluid tapped from the conduit 112'a and applied to open the check valve 80a through the conduit 138a.

Fluid entering the conduit 72a from the head ends of the respective cylinders passes into the low pressure pump 64a to be recrculated. Since the volume of fluid removed from the head ends of the cylinders 50a and 56a is greater than the volume required at their rod ends,

by virtue of the volume of the respective piston rods, the excess fluid drained from the head ends of the cylinders is passed through the conduit 98a into the tank. Passage of the excess iiuid through the conduit 98a may take place at this time since the hydraulic actuator 104a has moved the two-position valve 96a to its open position by virtue of the pressure supplied from the conduit 74a through the conduit 106a.

The pumps 64a and 66a continue to operate until the end clamp assembly 42a is moved into engagement with the car. Since all of the pumps 64a and 64b and 66a and 66h are of a positive displacement type, an equal volume of iluid is pumped into the respective end clamp operating motors at either end of the platform, thus assuring that each motor strokes exactly the same distance to thereby center the car upon the platform.

As the car is moved into its centered position and the end clamps begin to work against each other, pressure begins to back up in the clamp operating motors and, when the pressure in the conduit 74a exceeds the setting of the pressure release valve 94a, the valve 94a opens to permit the pressure fluid to be drained olf into the reservoir R. Pressure from the high pressure pump 66a cannot enter the conduit 74a due to the orientation of the pilot operated check valve 88a. The release pressure of the valves 94 is selected to be somewhat higher than the pressure necessary to move the loaded car to center it on the platform. Y

Both pumps 64a and 66a continue to operate until the pressure in the conduit 82a reaches a Value of approximately 1,000 p.s.i. At this time, the pressure switch a is actuated to open the normally closed contacts 12011. Since the contacts 12011 and 12011 are connected in parallel, it is only when both of these contacts are open that any change takes place in the electrical control circuit.

Upon opening of both of the contacts 120a and 12017, the circuit across the supply lines 136 and 134 through the clamps up operating relay U is opened, and this relay is thus deenergized. Upon deenergization of the relay U, the contacts Ub, Uc and Ud open to deenergize the low pressure pump driving motor 68.

However, the high pressure pump driving motor 70 remains energized since the relay MB controlling the contacts MBb, MBC` and MBd remains locked in through its contacts MBa and the normally closed contacts R2a. Thus, the high pressure pumps continue to supply fluid to the various motors to firmly maintain the end clamps 40a and 40b in clamping engagement with the car. Pressures in excess of 1600 p.s.i. are bled oif from the high pressure pump circuit through the pressure release valves 114g and 114b.

Since it is undesirable to actuate the platform oscillating unit 38 until the car is clamped, the actuating circuit for the motor 38M includes a pair of contacts 120C and 1200i which are respectively actuated to their closed positions when the operating pressure in the conduits 112a and 11211 exceeds 1,000 p.s.i. In addition tothe contacts 120e and 120d, the platform lock assemblies include limit switches having normally open contacts LSa and LSI; which are closed only when the platform lock linkage is located in its released position.

When the contacts LSa, LSb, 120C and 120:1 are closed,

a circuit is completed from the supply line 136 to lthe point 140.

At this time, the oscillating drive motor 38M may be energized by manually closing the Slow push button 142. This completes a circuit from the point 140 to the other side of the supply line 134 through a motor control relay M. Ilnergization of the relay M closes a lock in contact Ma which by-passes the contacts 142 and connects the motor 38M to the 220 volt supply by closing the contacts Mb, Mc and Md. The completion of this circuit causes the motor 38M to begin to drive. Secondary resistors in the motor rotor circuit are, at this time, cut into their full value. However, upon actuation of the Fast button 144, relay 1A is energized. Energization of relay 1A closes its lock in contacts 1Aa and likewise closes contacts 1Ab and 1Ac which short out a fixed portion of the secondary resistors to thereby cause the motor 38M to drive at a faster speed.

Actuation of the motor 38M causes the platform to oscillate upon its mounting mechanism in a manner fully set forth in the Albert Musschoot Patent, No. 2,850,184, issued September 2, 1958. Oscillation of the platform is continued until the car is unloaded.

When the car is unloaded, the operator actuates stop button 146, thereby opening the supply circuit to the relays M, 1A, and a time delay relay TR. When the relay M is deenergized, the contacts Mb, Mc and Md are opened to deenergize the motor 38M. v

The function of the time delay relay TR is to prevent retraction of the end clamps 40a and 40b before the platform has ceased oscillating. The relay TR controls normally closed contacts TRa which are set to close a xed time interval after the deenergization of the relay TR. When the contacts TRa close, a circuit is completed across the supply lines 134 and 136 through a second timing relay TR2. Energization of TR2 opens normally closed contacts TRZa which are set to open a fixed time interval after TR2 is energized. Opening of the contacts TRZa opens the supply circuit to a relay R2 which controls a pair of normally closed contacts R2a connected in series with the contacts TRa.l When the contacts R 2a close, the circuit is conditioned to permit the actuation of the hydraulic circuit to lower the end clamps and simultaneously elevate the platform lock cylinders to their locking position.

To perform this operation a Down button 148 is manually actuated to complete the circuit from the contacts RZa to the supply line 134 through a pair of normally closed pressure contacts 118:2 and 118b respectively of the corresponding pressure switches which are connected in parallel, and normally closed contacts Ue and the clamp down controlling relay D. Energization of the relay D closes a set of lock in contacts Dc and simultaneously closes the contacts Dd, De and Df to connect the low pressure pump drive motor 68 to the 220 volt supply. The connections through the various contacts Dd, De and Df are such as to cause the motor 68 to drive in the reverse direction from that in which it drives upon energization of the clamps up operating relay U. Energization of the relay D also opens the contacts Da, thus opening the circuit to the high pressure pump drive motor 70.

To retract the end clamps 40a and 40b and to engage the platform lock assemblies, the low pressure pump 64a is driven in a direction to pump uid through the conduit 72a to the conduits 76a and 78a and thus to the respective head ends of the platform lock cylinder 56a and end clamp operating motor 48a.

Fluid is drained from the rodends of the respective cylinders through the lines 80a and 84a and hence to conduit 82a. Fluid ows from conduit 82a through the pilot operated check valve 88a which is opened at this time since pilot pressure is supplied from the conduit 72a to the conduit 90a; Fluid flowing from the rod ends of the respective cylinders thus passes through the valve 88a into the conduit 74a and hence through the side ofthe low pressure pump 64a which acts as an intake during this portion of the operation. Fluid under pressure passes from the conduit 90a to the two-way valve actuator 10811 to shift the valve 96a to its blocking position, thus preventing pressure fluid from owing from the conduit 72a to the tank'through the conduit 98a. EX- cess iluid necessitated by the volume differential caused by the volume of the respective piston rods is withdrawn from the reservoir through the conduit 98a and passes through the one-way check valve 102a into the conduit 74a and thence to the intake side of the pump 64a. The pump 64a continues to supply uid under pressure to the head ends of the respective cylinders until the pressure in the conduit 72a builds up to a value of approximately 400 p.s.i., at which time the normally closed contacts 11811 are opened. As in the clamping operation, both contacts 118a and 118b must open to break the circuit through the down control relay D. When the relay D is deenergized, the contacts Db, De and Df are opened, thereby opening the supply circuit to the low pressure pump drive motor 68.

While we have described but one embodiment of our invention, it will be apparent to those skilled in the alt that the disclosed embodiment is capable of modication.- Therefore, the foregoing description is to be considered exemplary ratherthan limiting and the true scope ofour invention is that defined in the following claims:

Having thus described the invention, we claim:

1. In a box car unloader, or thelike, includinga platform for supporting -a box car, means for vibrating said platform to alternately elevate opposite ends of a car supported thereon, and means for clamping a car in a central position upon said platform; the improvement wherein said clamping means comprises a pair of oppositely disposed clamp members movable into and out of clamping engagement with a car located on said platform, a reversible hydraulic motor connected to each of said clamp members for moving the associated clamp member into `and out of clamping engagement with said car, a reversible first positive displacement pump means connected to each of said motors, both of said rst pump means being drivable in a rst direction to actuate the associated motor in clamp engaging movement and drivable in the opposite direction to actuate the associated motor in clamp retracting movement, a common reversible first drive means connected to both of said rst pump means to simultaneously drive both of said first pump means in the same direction, a second positive displacement pump means connected to each of said motors, a common second drive means connected to both of said second pump means and operable to simultaneously drive both of said second pump means to actuate the associated motor in clamp engaging movement, and control means comprising means operable to actuate said second drive means when said iirst drive means is actuated to drive said first pump means in clamp engaging movement, and means for stopping said first drive means after a predetermined clamp engaging pressure is achieved in both of said motors while maintaining said second drive means in operation to continue to apply clamp engaging pressure to both of said motors.

2. The combination defined in claim l including platform locking means engageable with said platform to prevent movement thereof, and means connected to said rst and said second pump means for moving said locking means out of engagement with said platform as said clamp members are moved into engagement with said car and for moving said locking means into engagement with said platform as said clamp members are moved out of engagement with said car.

3. The combination defined in claim 2 wherein said control means include switch means for starting and stopping said vibrating means, and means for rendering said switch means ineffective to start said vibrating means until said locking means are moved out of engagement with said platform.

4. 'I'he combination defined in claim 2 wherein said control means include switch means for starting and stopping said vibrating means, and means for preventing actuation of said first drive means to drive said motors in a clamp retracting movement until a predetermined time interval after said switch means have been actuated to stop said vibrating means.

5. `rIn a box car unloader, or the like, including a platform for supporting a box car, means for vibrating said platform to alternately elevate opposite ends of a` car supported thereon, and means for clamping a car in a central position upon said platform; the improvement wherein said clamping means comprises a pair of oppositely disposed clamp members movable into and out of clamping engagement with opposite ends of a car located on said platform, a reversible hydraulic motor connected to each of said clamp members for moving the associated clamp member into and out of clamping engagement with said car, reversible positive displacement pump means connected to each of said motors, said pump means each being drivable `in a rst direction to actuate the associated motor in a clamp engaging movement and drivable in the other direction to actuate the associated motor in a clamp retracting movement, a

common reversible drive means connected to both ofV ing said common drive means to drive both of said pump means `in either of said directions, locking means adjacent either end of said platform and engageable with said platform to prevent movement thereto, a hydraulic motor associated with each of said locking means for moving said locking means into and out of engagement with said platform, and means connecting each of said motors for said locking means to said pump means in parallel with said motors for said clamping members to move said locking means out of engagement with said platform as said clamping means are moved into engage- 10 ment with said car and to move said locking means into engagement with said platform as said clamp means are moved out of engagement with said car.

6. The combination defined in claim 5 including switch means for starting and stopping said vibrating means,

and means for preventing said switch means from starting said vibrating means until said locking means are located out of engagement with said platform.

References Cited in the le of this patent UNITED STATES PATENTS

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