Stacker control

Details Stacker control Stacker control

1999-01-06

2001-04-24

Ryznic, John E. (Department: 3745)

Power plants

Pressure fluid source and motor

Having condition responsive control in a system of distinct...

C091S446000

Reexamination Certificate

active

06220027

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a stacker control.
Shelf stackers (special sorts of fork lift trucks, the fork of which can be lifted and lowered vertically but also have additional fork functions such as additional lift, thrust, turning the fork), in particular stackers for high storage racks, comprising swing-shift forks require a high degree of safety during control of the fork if they operate within a laterally defined aisle area, e.g. between rows of shelves. For reasons of space the aisle area is often so limited that uncontrolled turn and thrust movements of the fork may easily lead to collisions. Therefore, for such complicated maneuvering operations, shelf stackers are often operable by means of a computer which guides the stacker control by simultaneously swinging and shifting the fork, so that the fork does not collide with the rows of shelves. To this end, the computer must not only be informed in a precise manner about the actual position of the fork, but the stacker control must be precisely guidable by the computer, i.e. exactly in proportion with the control signals. A further problem encountered in the case of a precise proportional control of the swing-shift fork arises from the fact that hydraulic motors which carry out swinging and shifting operations, respectively, optionally at the same time, require clearly distinct flow rates, e.g. in a ratio of 1:3 to 1:6, and the control of the hyraulic motor with the smaller rate must also be reliably proportional in cases where the hydraulic motor requiring the larger amount is moved at the same time.
It is known in practice that in the stacker control of a shelf stacker a three-way flow regulator (3-way control valve) and a proportional directional control valve with upstream supply regulator are assigned to each hydraulic motor to achieve precise proportionality during control, as is e.g. required for maneuvering operations within narrow aisle areas. Such a stacker control is not only very troublesome and expensive, but requires a lot of space, which is not readily available in the case of shelf stackers, because of the complicated hydraulic components. Therefore, such a stacker control is also very troublesome for the reason that a specific neutral circulation switching function of the hydraulic medium, which is delivered by the source of pressure, is required, for instance in case of pilot pressure tapping (PSL load sensing principle), in the directional control valves.
Furthermore, it is known in practice that the stacker control of such shelf stackers is equipped with a plurality of pressure balances, directional control valves and lowering brake valves (drop-rate braking valves) to save space and costs. However, it is thereby not possible to achieve a sufficiently proportional control, as is e.g. needed for maneuvering operations within limited aisle areas. Such shelf stackers first must move out of the aisle area for the swing-shift adjustment of the fork, and must again move into the aisle with the adjusted fork, or the aisle areas between rows of shelves must be made correspondingly wide in relation with the width of the fork.
In control devices which are known from WO86/06142, U.S. Pat. No. 3,911,942, U.S. Pat. No. 3,987,623 and DE-A-1 95 49 150, control priority is given to a selected group of consumers over other consumers. The control devices contain three-way pressure balances or multi-way valves which serve flow control purposes.
Further prior art is found in U.S. Pat. No. 4,517,800, U.S. Pat. No. 4,733,533, DE-A-301 61 57 and U.S. Pat. No. 4,543,031.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a stacker control of the aforementioned type which is inexpensive, space-saving and comfortable and which permits a safe maneuvering of the swing-shift fork within narrow aisle areas, possibly in computer-assisted fashion.
This object is achieved with the following features of claim
1
.
With the help of the three-way pressure balance, priority is always given in a constructionally simple and inexpensive manner to the hydraulic motor in which under simultaneous control of a further hydraulic motor the risk of a no longer exactly proportional control is given, i.e. normally to the hydraulic motor having the lower flow rate. In a shelf stacker or stacker for high storage racks, this is normally the hydraulic motor which is in charge to turn the fork about the vertical axis. Thanks to the action of the three-way pressure balance, the further hydraulic motor(s) only receive(s) the excess amount so that at least the preferential hydraulic motor can be controlled in a precisely proportional manner under all operating conditions. The installation space for the stacker control and also the equipment efforts are reduced because a few compact components are sufficient and because the three-way pressure balance permits a very simple neutral circulation switching through which the hydraulic medium delivered by the source of pressure, which is normally operated electrically, passes at a small throttling resistance and small counterpressure into the return means. The proportional directional control valve of the preferred hydraulic motor relieves the two work lines to the return means in its zero position so that a strong control pressure drop which can be used for the neutral circulation switching is given. The further hydraulic motor is also controllable in a precisely proportional manner via the three-way flow regulator, with a three-way flow regulator, the three-way pressure balance and the further directional control valves cooperating for the establishment of the neutral circulation circuit.
According to another feature of the invention the swing-type hydraulic motor for the fork turn function is the preferential hydraulic motor which requires a smaller flow rate than the further hydraulic motors and in which a precise proportional control is important for difficult maneuvers of the swing-shift fork.
According to another feature the precise proportional control is possible with the help of the proportional directional control valve which simultaneously contains the regulating aperture for the three-way pressure balance.
According to another feature there is provided a simple load holding device for hydraulically blocking each hydraulic motor and for holding a load without any leakage. The load holding device with the load holding valves which can alternately be pilot-operated from the work lines permits a sensitive motional control under load and helps, above all, to simplify the neutral circulation switching because in a load holding situation both work lines are relieved downstream of the directional control valve, and a pilot pressure for the three-way pressure balance is automatically present which switches the three-way pressure balance into the neutral circulation position. Furthermore, the load holding device permits the use of a short directional control valve which is open in the zero position and which, therefore, does not require separate flow paths for the neutral circulation.
According to another feature the pilot pressure for the three-way pressure balance and the neutral circulation switching is tapped in a constructionally simple manner without the directional control valve, which is thus compact, requiring any troublesome constructional measures.
According to another feature, the three-way pressure balance gives supply priority to the selected hydraulic motor over the further hydraulic motor(s) irrespective of whether and how said motors are acted upon.
According to another feature, the three-way pressure balance is of a particularly simple construction.
According to another feature, if no further hydraulic motor is acted upon, the pressurized fluid delivered by the source of pressure is guided in the neutral circulation circuit with the throttling loss into the return means via the directional control valve of the further hydraulic motor or said directional control valve and the three-way flow regulator arranged upstream of said valve.
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