WO2004019748A1

WO2004019748A1 - Method for controlling tunnel dishwasher, and tunnel dishwasher

Info

Publication number: WO2004019748A1
Application number: PCT/FI2003/000628
Authority: WO
Inventors: Timo Värpiö
Original assignee: Hackman Metos Oy Ab
Priority date: 2002-08-28
Filing date: 2003-08-27
Publication date: 2004-03-11
Also published as: DE10393158T5; FI20021539A; FI115195B; AU2003255553A1; FI20021539A0

Abstract

A method for controlling a tunnel dishwasher and a tunnel dishwasher imple-menting the method. The method comprises: operating a conveyor (5) forward (F), whereby the dishes to be washed (11) move forward on the conveyor (5) in relation to a wash zone (2, 3, 4). The conveyor (5) is then operated in re-verse (R), whereby the dishes to be washed (10) remain substantially station-ary in relation to the wash zone (2, 3, 4). The conveyor (5) is operated in re-verse (R) at a speed which is substantially higher than the speed of the for-ward (F) movement.

Description

METHOD FOR CONTROLLING TUNNEL DISHWASHER, AND TUNNEL DISHWASHER

BACKGROUND OF THE INVENTION

[0001] The invention relates to a method for controlling a conveyor of a tunnel dishwasher, the method comprising:

[0002] operating the conveyor forward, whereby the dishes to be washed move forward on the conveyor in relation to a wash zone;

[0003] operating the conveyor in reverse, whereby the dishes to be washed remain substantially stationary in relation to the wash zone. [0004] The invention further relates to a tunnel dishwasher comprising:

[0005] at least one wash zone;

[0006] a conveyor arranged to move the dishes to be washed through the wash zone; [0007] a power unit configured to operate the conveyor forward, whereby the dishes to be washed move forward on the conveyor in relation to the wash zone and to operate it in reverse, whereby the dishes to be washed remain substantially stationary in relation to the wash zone.

[0008] In a tunnel dishwasher the dishes to be washed are ar- ranged onto carriers, typically a rack, which are conveyed on a conveyor, or a sledge, of a conveyor device through the zones of the dishwasher. The conveyor moves back and forth in the longitudinal direction of the machine, rotated by a crankshaft. This is an essential difference between a tunnel dishwasher and a commonly used dishwasher type, i.e. a conveyor chain machine, in which the conveyor chain moves only forward. A tunnel dishwasher typically comprises successive pre-wash, wash and rinsing zones.

[0009] Arranged at predetermined intervals in the longitudinal direction of the machine, the tunnel dishwasher comprises hooks that may be fitted to the conveyor. When the conveyor is operated forward, the hooks push the rack forward. When the conveyor starts to move in reverse, the hooks come down and the racks remain stationary on the guide tracks. When the conveyor then starts a new forward movement, the hooks go up, gripping the rack and moving it forward until the next reverse movement begins. Alternatively, the tunnel dishwasher can be implemented by arranging the hooks to the guide tracks in which case the conveyor moves the tracks forward by the impact of the friction between the conveyor and the rack. The hooks arranged to the guide tracks prevent the racks from moving backward when the conveyor is operating in reverse.

[0010] A conveyor device that moves back and forth is easier to manufacture than a chain conveyor and, in addition, it is easier to keep clean.

[0011] A disadvantage of a back and forth moving conveyor is that it is uneconomical in operation, because in a tunnel dishwasher the racks and the dishes to be washed proceed only when the conveyor is moving forward.

Therefore, if the machine is to operate at a capacity of 200 washed racks per hour, for example, the actual average speed of the conveyor must be 400 racks per hour. In other words, when a rack moves, its speed is double the capacity speed of the machine. This causes a problem, because a dish arranged in the rack passes the wash and rinse jets of the machine at this double speed, and the dish is thus subjected to a rinsing flow which is half the flow provided by a conveyor chain dishwasher of a corresponding capacity. The reason for this is that the length of the back and forth movement is longer than the dimension of an individual dish in the direction of movement and therefore the dish goes through the entire rinsing water jet at the applied speed of movement. The uneconomical operation of the machine is particularly empha- sized in the rinsing zone, where the depth of the rinsing jet in the direction of propagation is typically only about 30. mm. In order for the rinsing power of the tunnel dishwasher to be equal to that of a conveyor chain dishwasher of a corresponding capacity, the rinsing flow, i.e. water consumption, should be at least double compared to the latter. It is typical that the rinsing water specifi- cally, and the heating of the water in particular, causes the highest operating costs of a tunnel dishwasher.

BRIEF DESCRIPTION OF THE INVENTION

[0012] It is an object of the present invention to provide a method for controlling a conveyor device of a tunnel dishwasher, and a tunnel dish- washer that allow the above problem to be solved.

[0013] The method of the invention for controlling a conveyor device of a tunnel dishwasher is characterized by: operating the conveyor in reverse at a speed that is essentially higher than the speed of the forward movement. [0014] The tunnel dishwasher of the invention is characterized in that the speed of the reverse movement of the conveyor is substantially higher than the speed of its forward movement.

[0015] An advantage of the invention is that since the speed of the reverse movement of the conveyor is substantially higher than speed of its forward movement, the use of the rinsing water can substantially enhanced. This allows the wash result to be improved without reducing the capacity and increasing the water consumption of the machine, because the dish to be washed stays under the rinsing jets for a substantially longer time than in a prior art machine. The rinsing flow acting on the dish is therefore substantially greater than in a prior art machine of the same capacity.

[0016] Another alternative that the invention provides is reduced consumption of rinsing water, because the amount of water flowing through a rinsing nozzle in a time unit can be reduced without impairing the rinsing result. [0017] A third alternative made available by the invention is increased capacity of the machine as a whole, without compromising the rinsing result.

[0018] According to a preferred embodiment of the invention conveyor movement is caused by an electrically driven spindle motor or linear mo- tor, which are compact in structure, maintenance-free and produce direct linear motion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the following the invention will be described in greater detail with reference to the accompanying drawings, in which Figure 1 is a schematic, partly sectional side view of an embodiment of a tunnel dishwasher of the invention; and

Figure 2 is a schematic, partly sectional side view of a second embodiment of the tunnel dishwasher of the invention.

DETAILED DESCRIPTION OF THE INVENTION [0020] Figure 1 is a schematic, partly sectional side view of an embodiment of a tunnel dishwasher of the invention. The tunnel dishwasher 1 - hereinafter the dishwasher 1 - comprises a pre-wash zone 2, a wash zone 3, and a rinse zone 4 arranged immediately one after the other. In the pre-wash zone 2, the pre-wash takes place, in the wash zone 3 the main wash and in the rinse zone 4 the rinsing. The washing and rinsing means belonging to the zones and the arrangements associated therewith are known per se and therefore they will not be discussed in greater detail in this context. It should be noted that a dishwasher does not necessarily contain all the zones mentioned above, and the zones do not necessarily have to be arranged in contact with each other.

[0021] The dishwasher 1 further comprises a conveyor 5 having a longitudinal body 6. The conveyor 5 moves back and forth in the longitudinal direction of the machine in such a way that its back and forth movement is usually 50 ... 150 mm, although some other length of movement is also possi- ble. The body 6 of the conveyor is provided with hooks 7, the distance between the hooks being arranged to correspond to the length of the movement of the conveyor 5 or to be smaller than that. The hooks 7 are fixed to the conveyor by means of a hook axis 8 and they are able to rotate on the axis 8 in relation to the body 6 of the conveyor. The dishwasher 1 still further comprises guide tracks 9 leading through the wash zones, the tracks being depicted with a dashed line in the Figures.

[0022] Dishes 11 to be washed in the dishwasher are arranged into racks 10. The racks 10 are supported by the guide tracks 9 in the dishwasher. The hooks 7 are weighted so that they tend to rotate into a vertical position against a hook support 19 by impact of gravity, the first and third hook 7 from the left being shown in this position in the Figure. In this position the top part of the hooks 7 is above the upper surface of the guide tracks 9.

[0023] When the hooks move forward together with the conveyor 5, i.e. in the direction shown by arrow F, one of them takes hold of a rack 10 and pushes it forward on the guide tracks 9 for a distance equal to the length of the movement of the conveyor 5. As the forward movement of the conveyor 5 stops, it starts to move in reverse, i.e. to the direction shown by arrow R. When the oblique rear surface of the hook 7 during this movement then meets a rack 10, the rack 10 presses the hook 7 so that it rotates in a clockwise direction into a position shown in the Figure by the second and fourth hooks 7 from the left. In this position the hook does not move the rack with it, but the hook moves underneath the rack backwards in relation to the rack. When the hook has passed the rack 10, it turns into a vertical position again. As the reverse R movement of the conveyor 5 stops, the conveyor again starts to move forward into direction F during which movement the hooks 7 that are in a vertical position again move the racks 10 forward for the length of the movement of the conveyor 5. The conveyor 5 moves the racks 10 stepwise through the dishwasher 1.

[0024] The movement of the conveyor 5 is caused by a power unit 12, which in the embodiment illustrated in Figure 1 is a spindle motor. The spindle motor comprises a motor and gear part 13 and a spindle 14 making a back and forth linear movement by impact of the motor and the gear. The spindle motor is a power unit known per se and it will not be discussed in greater detail here. The motor and gear part 13 is attached in relation to the body of the dishwasher 1 , whereas the end of the spindle 13 is attached to a fixing point 16 provided in a flange 15 of the body 6 of the conveyor. The direction of movement of the spindle 13 is substantially parallel with the directions of movement F, R of the conveyor 5.

[0025] The spindle motor is associated with a reverser device 17 and a control unit 18. Controlled by the control unit 18, the reverser device 17 converts electric current entering the device to produce the desired direction and speed of movement of the spindle 14.

[0026] The power unit 12 operates such that it moves the conveyor substantially slower forward, i.e. in direction F, than in the reverse direction, i.e. in direction R. The average speed of the conveyor 5 in the forward direction F may be, for example, 150 racks per hour and 250 racks per hour in the reverse direction R, the dishwasher capacity thus obtained being 100 racks per hour. Since in this example the speed of the movement that takes the rack forward is only ³/Λ of the speed corresponding to the dishwasher capacity, the period for which the dishes 11 in the rack 10 remain under the rinsing jets is 33% longer. The rinsing flow acting on the dishes 10 is thus 33% greater than in a prior art machine of the same capacity. In other words, the rinsing of the dishes is significantly more effective.

[0027] A second alternative provided by the invention is to reduce the consumption of rinsing water, because the amount of water flowing through the rinsing nozzle in a time unit can be reduced without impairing the rinsing result. A third alternative is to increase the capacity of the machine as a whole without compromising the rinsing result.

[0028] It is obvious that the speeds of movement and their ratio may differ from those given here. [0029] The power unit 12 providing a linear movement can also be a linear motor, pneumatic actuator, hydraulic actuator, or the like. [0030] The dishwasher can also be implemented as a version in which the hooks 7 are arranged to the guide tracks 9. In this type of dishwasher the conveyor 5 moves the racks 10 forward by impact of the friction between the conveyor 5 and the rack 10. The hooks arranged to the guide tracks prevent the racks from moving backward when the conveyor 5 operates in reverse, whereas during a forward movement the hooks move aside so as not to be in the way of the forward moving racks 10.

[0031] Figure 2 is a schematic, partly sectional side view of a second embodiment of a tunnel dishwasher of the invention. The dishwasher 1 is similar to the embodiment shown in Figure 1 , except for the power unit 12: instead of a linear movement, the power unit 12 produces a rotating motion. In this case the power unit is an electric motor, such as a cage induction motor.

[0032] The rotating motion produced by the power unit 12 is transmitted by power transmission 20 to the conveyor 5, which comprises a first transmission gear 21 and a second transmission gear 22, and, in contact with the latter, a linear power transmission member 23 arranged to the conveyor 5. The operation of the power transmission 20 may be based on gear transmission, for example, in which case the first and the second transmission gears 21 , 22 are gearwheels and the linear transmission member 23 is a gear rack, or it may be based on friction wheels and surfaces, belt or chain drive, or on other similar transmission solutions known per se.

[0033] The power unit 12 rotates both in a first and in a second, opposite direction of rotation. The first direction of rotation moves the conveyor 5 forward in the direction of arrow F. When the conveyor 5 has proceeded for a predetermined distance, the direction of rotation of the power unit 12 is reversed, whereby the direction of movement of the conveyor 5 changes to take place in reverse, i.e. in the direction shown by arrow R. The operation of the conveyor 5 as such is similar to description of Figure 1.

[0034] Controlled by the control unit 18, the reverser device 17 con- verts the electric current entering the device to obtain the desired direction and speed of rotating motion. Limit switches or similar control means known per se can be utilized to control the power unit 12 so as to identify when the conveyor 5 has moved to its extreme position, for example. The speed of the forward movement F is substantially slower than that of the reverse movement R, whereby advantages described already in connection with Figure 1 are obtained. [0035] In addition to an electric motor, the power unit 12 producing a rotating or a revolving motion may be a pneumatic or a hydraulic actuator.

[0036] The drawings and the related specification are only meant to illustrate the idea of the invention. The details of the invention may vary within the scope of the claims. The hooks 7 may therefore be formed otherwise than in the Figures. At least some of the hooks 7 may be arranged into groups of several hooks, the distance between successive hooks being smaller than the distance between the groups. The movement of the hooks 7 from one position to another may be implemented also in other ways known per se, by means of a mechanical control, for example.

Claims

1. A method for controlling a conveyor of a tunnel dishwasher, the method comprising: operating the conveyor (5) forward (F), whereby the dishes to be washed (11) move forward (F) on the conveyor (5) in relation to a wash zone (2, 3, 4); operating the conveyor (5) in reverse (R), whereby the dishes to be washed (11) remain substantially stationary in relation to the wash zone (2, 3,

4), characterized by: operating the conveyor (5) in reverse (R) at a speed that is essentially higher than the speed of the forward (F) movement.

2. A method according to claim 1, characterized by: arranging the dishes to be washed (11) into racks (10) in which they are carried through the tunnel dishwasher (1) by the conveyor (5).

3. A Tunnel dishwasher comprising at least one wash zone (2, 3, 4); a conveyor (5) arranged to move the dishes to be washed (11) through the wash zone (2, 3, 4); a power unit (12) configured to operate the conveyor (5) forward (F), whereby the dishes to be washed (11) move forward (F) on the conveyor (5) in relation to the wash zone (2, 3, 4) and to operated it in reverse (R), whereby the dishes to be washed (11) remain substantially stationary in relation to the wash zone (2, 3, 4), c h a r a c t e r i z e d in that the speed of the reverse (R) movement of the conveyor is substantially higher than the speed of its forward (F) movement.

4. A tunnel dishwasher according to claim 3, characterized in that the power unit (12) is an electric motor.

5. A tunnel dishwasher according to claim 4, characterized in that the electric motor is a spindle motor or a linear motor.

6. A tunnel dishwasher according to claim 3, characterized in that the power unit (12) is a pneumatic actuator.

7. A tunnel dishwasher according to claim 3, characterized in that the power unit (12) is a hydraulic actuator.