Patent Application
20160194845
The invention relates to a gripper device for a trash rake cleaner. Trash rakes are applied at water works, for instance at water treatment plants, pumping plants, hydroelectric power plants and cooling water installations. A trash rake prevents passage of material entrained by the water. Once a great deal of entrained material has accumulated in front of the trash rake, the trash rake has to be cleaned since the throughflow of water would otherwise be blocked. A trash rake cleaner is utilized for this purpose. A trash cleaner comprises, among other parts, a gripper which can grab the accumulated material out of the water.
In conventional trash rake cleaners the gripper must be opened and closed by means of a hydraulic system. A drawback of hydraulics is that the mineral or synthetic oils used as hydraulic fluid are harmful to the environment. Using hydraulics for water supply can result in water contamination. Although hydraulic fluids on the basis of vegetable oils are meanwhile available, these have the drawback that they have to be completely replaced about every four years. This makes such hydraulic systems maintenance-intensive.
GB 761644 describes a gripper which is operated with two groups of cables. The first group of cables serves the purpose of opening and closing the gripper and the second group of cables serves for raising and lowering the gripper.
This has the drawback that a drive must be provided for both the first group of cables and the second group of cables. Particularly in the case of a gripper with a relatively great weight, multiple cables with associated drum and drive will have to be provided for the purpose of raising and lowering the gripper. In addition, a separate drum with drive must be provided for each of the cables for opening and closing the gripper.
A further drawback is that the groups have to be adapted to each other so as to prevent unintentional opening or closing of the gripper. This makes the required control complex.
An object of the invention is to obviate the above stated problems and to provide a gripper device for a trash rake cleaner which does not incorporate any hydraulics and which, even when the gripper has a relatively great weight, needs only a minimum number of drives, and the construction of which is effective and safe.
This object is achieved with the gripper device for a trash rake cleaner according to the invention, comprising:
In the gripper device according to the invention two cables serve for both raising and lowering and for opening and closing of the gripper. It is hereby possible to dispense with a separate cable or cables, or separate hydraulics, for the purpose of opening and closing the gripper.
The construction moreover guarantees that the gripper remains in the desired end position, also when the cables are not displaced wholly synchronously for raising or lowering the gripper. This is because, when the gripper is opened, the force required to rotate the gripper arm to the closed position is greater than the force required to hold the gripper in the open position. So even when the tensioning forces in the cables differ to some extent due to the non-synchronous running of the hoisting means, the gripper will remain in the open end position. A similar consideration applies to the closed end position in which the force for opening the gripper is greater than that for closing thereof.
In other words, the gripper is movable to a selected one of the open end position and the closed end position by respectively taking in and paying out the first cable relative to the second cable, while simultaneous hoisting or lowering of the cables respectively raises or lowers the gripper into the selected end position.
The moment arm of a force relative to a point of rotation is defined by the perpendicular distance of this rotation point to the line of force, i.e. the line in the direction in which the force acts, this line passing through the point of engagement of the force (line of action).
An additional advantage of the gripper device according to the invention is that operation is possible in simple manner at greater depths than with conventional gripper devices for trash rake cleaners. In conventional gripper devices the vertical distance which the gripper can cover is limited to about 15 metres, for instance because at greater distances the hydraulic lines begin to bend because they are carried along by the flow of the water, and are moreover likely to begin leaking. There are situations however in which trash rakes lie at a much deeper level, even up to 100 metres. In current practice these trash rakes are cleaned manually since conventional trash rake cleaners will not suffice for this purpose. With the invention it becomes possible to clean such deeper level trash rakes. This can be realized by applying the correct cable length. Because no hydraulics arc required according to the invention, no additional (complex) provisions need be provided on the gripper or hoisting installation to make them suitable for such great vertical distances. It is also possible to dispense with long hydraulic lines for the purpose of spanning these distances.
It is noted that it is possible to provide a plurality of cables, for instance when the weight of the gripper requires this. In this case a first group and a second group of cables are provided on either side of the rotation axis. Upward movement of the first group of cables relative to the second group of cables will in that case carry the gripper to the open end position, and upward movement of the second group of cables relative to the first group of cables will carry the gripper to the closed end position. Once again a separate cable is in this case not required for the purpose of opening or closing the gripper. This makes the construction according to the invention relatively simple, wherein it can in addition be embodied with relatively few components. This also makes repair simpler.
The points of engagement are provided on either side of the rotation axis, i.e. they are provided on either side of a vertical line through the rotation axis. In other words, the rotation axis is situated on the gripper arm at a position between the points of engagement on this same gripper arm.
According to the invention the gripper device can also be utilized for applications other than a trash rake cleaner.
In a currently preferred embodiment the gripper device complies with the ATEX (ATmosphères EXplosibles) guideline wherein sparking is prevented. This is particularly relevant at water treatment plants because of methanogenesis. The gripper for instance comprises components, such as teeth, which prevents sparking. The gripper is for instance provided with a layer which prevents sparking. The gripper for instance comprises aluminium or bronze or an alloy thereof. The device for instance comprises a motor which complies with the ATEX guideline.
According to the invention each hoisting means is driven by a separate drive, wherein the gripper device further comprises a controller connected to the drives for controlling the drives by transmitting a control signal with the controller, wherein the controller has a hoisting mode in which the controller is configured to transmit the same control signal to both drives for the purpose of raising or lowering the gripper, wherein each drive comprises a slippage coupling or a motor with internal slippage such that synchronous running of the hoisting means is automatically realized in the hoisting mode.
The controller can transmit the control signal in wireless or wired manner to the drive.
The controller for instance comprises a frequency control. The controller preferably comprises only one frequency control for controlling both drives.
According to the invention it is not necessary to synchronize the driving. This is because slippage, also referred to as internal slippage, occurs in many types of motors, such as in the case of electric motors and hydraulic motors. This is also referred to as electromagnetic slippage in the case of electric motors. This slippage is the difference between the rotation frequency of the motor and the drive frequency, often expressed as a percentage of the drive frequency. The load determines the slippage of the motor. If the gripper is displaced and the motors are not synchronized, the motor with the heavier load will decelerate and the motor with the light load will accelerate. A uniform distribution of the load is hereby obtained automatically. It is hereby possible to dispense with a synchronization mechanism.
The motors preferably have substantially the same specifications. This limits the complexity. A balanced construction is moreover hereby obtained. The drives are not coupled and function independently. As a result of the slippage the path covered by the respective cable in the case of an increasing load will be shorter, while the path covered in the case of a decreasing load will be longer. The power supplied by the drives hereby remains substantially constant. If motors of about the same power are applied, this will result in a uniform distribution of the load.
It is noted that conventional gripper devices comprise encoders which measure the rotation and/or rotation speed of the drives, wherein the output of the encoders is used as feedback in the control of the drives. Since synchronization is not necessary according to the invention, it is possible to dispense with encoders or similar sensors, and likewise with a control with feedback.
In a preferred embodiment the controller comprises a switch for switching between the hoisting mode and a gripper mode, in which gripper mode the controller is configured to transmit to at least one of the drives a control signal for the purpose of opening or closing the gripper which is not transmitted to the other drive.
Depending on the desired action, the controller, for instance a frequency control, will control both drives simultaneously (raising and lowering) or one of the drives (opening and closing). The drives preferably have the same orientation so that for raising and lowering purposes both drives produce a rotation in the same rotation direction.
The controller preferably transmits a control signal to only one of the drives in the gripper mode.
Each drive preferably comprises an electric motor, such as an asynchronous electric motor.
In a further preferred embodiment each drive is suitable to bear in any case 50% of the combined load, preferably in any case 75% and more preferably in any case 100%.
The drives are preferably suitable, in the case that one drive fails, to still be able to raise the gripper. The drives preferably have in any case sufficient power to raise the gripper in an empty state, i.e. without scooped-up material. That is, the minimum combined load that each drive can bear is at least equal to the weight of the gripper.
A typical gripper weight is 300-1500 kg. In addition, it is also possible to allow for the additional weight of the material for hoisting. Typical gripper devices are configured to carry 0.8-2.5 times the weight of the gripper in scooped-up material.
In the case of two cables with two drives, each drive is suitable to bear in any case 50% of the weight of the gripper, for instance 60%. In the case of four cables, two on each side of the rotation axis, and four drives, the drives are each suitable to bear in any case 25% of the weight of the gripper, preferably at least 33%. Two drives alternatively each carry two cables, wherein each drive is suitable to bear in any case 50% of the weight of the gripper, preferably at least 100%.
In an alternative embodiment the hoisting device further comprises a slippage coupling. This slippage coupling is configured to generate slippage when the drive used does not itself generate any slippage. The slippage coupling can also be used to enhance the above described effect.
In a preferred embodiment the gripper is mounted on a frame which is also provided with one or more redirecting means for redirecting the cables, wherein each cable is guided from the respective hoisting means along the one or more redirecting means to the gripper arm.
The redirecting means for instance comprises pulleys, sheaves or redirecting rollers.
As a result of the redirecting means the line of action of the force always remains the same even if the centre of gravity of the gripper changes due to opening or closing of the gripper. The line of action of the force is hereby well defined and proper operation of the machine is guaranteed. In addition, the cables are prevented from becoming entangled.
A further effect of the redirecting means is that the difference in moment arm of the moments of force around the rotation axis is increased. The cables run at an angle from the redirecting means to the points of engagement. This angle is greater than the angle which the cables would make without the redirecting means, since the distance between redirecting means and the gripper arm is shorter than the distance between the hoisting means and the gripper arm. This enhances the above described effect of holding the gripper in the selected end position.
The redirecting means are preferably provided relative to the hoisting means such that each cable runs substantially vertically in the area from the respective hoisting means to the redirecting means. The load of the gripper with frame is hereby distributed over the first and second hoisting means, i.e. over the drive thereof.
In a preferred embodiment the gripper comprises at least one stop for bounding the movement of the gripper arm.
The gripper for instance comprises two stops which form a bounding of the movement of the gripper arm in two rotation directions. The closed end position and the open end position are hereby defined.
In a preferred embodiment the rotation axis is provided outside the vertical plane midway between the cables.
Placing the rotation axis out of centre influences the angle which the cables make with the vertical plane. The moment arm of the moments of force are hereby also influenced relative to the rotation axis: the arm on the one side of the rotation point is increased, while the arm on the other side is reduced. A greater force is hereby exerted for the purpose of holding the gripper in the open or closed end position.
In the case the first cable is guided along a first redirecting means and the second cable along a second redirecting means, the rotation axis is not therefore located on the perpendicular bisector between the point at which the first cable is redirected by the first redirecting means and the point at which the second cable is redirected by the second redirecting means.
The rotation axis is preferably situated on the side of the first cable relative to the centre so that the moment arm for holding the gripper arm in the opened position is increased. Although the moment arm for holding the gripper arm in the closed position is hereby reduced, it is noted that in the closed position the gripper arm benefits from the weight of the load for the purpose of keeping the gripper arm closed.
For the same purpose the distance from the rotation axis to the first point of engagement differs in a further preferred embodiment from the distance from the rotation axis to the second point of engagement. Alternatively or additionally, an additional weight is provided for this purpose on the gripper.
In a preferred embodiment the rotation axis is arranged above a line connecting the first point of engagement to the second point of engagement. In other words, when an imaginary line is drawn from the first point of engagement to the second point of engagement, the rotation axis is then located above this line.
In a preferred embodiment each hoisting means comprises a drum, and the drums are arranged above one another. This makes the device according to the invention compact. The drums can moreover have the same rotation direction. Each hoisting means preferably comprises a drum of the same diameter. In another embodiment the drums are arranged adjacency of each other.
The invention can be applied with different cable lengths, for instance between 1 metre and 15 metres. In a preferred embodiment the cables have a length of at least 20 metres, more preferably at least 40 metres, more preferably at least 60 metres, still more preferably at least 80 metres and most preferably at least 100 metres.
The gripper device optionally comprises a detection system for detection of a slack cable. Slack can occur in a cable for instance if the gripper becomes jammed or if one of the cables snaps. If a cable is slack the tension in the other cables can become too great, which results in a hazardous situation. The detection system is preferably coupled to the controller so that this latter can stop movement of the gripper on the basis of detection of a slack cable. The controller is for instance adjusted, when a slack cable is detected, to switch off the drives, to switch on an emergency system, to generate an alarm and/or to move the gripper downward so that it can rest on a ground surface. The detection system for instance comprises redirecting rollers along which the cables of the device are guided and a sensor which is coupled to at least one of the redirecting rollers and which is configured to measure the force which the cables exert on the redirecting rollers and/or changes in this force.
The invention further relates to a gripper device for a trash rake cleaner, comprising
In other words, the cable forms a loop in which the redirecting means, and thereby the gripper, is suspended.
This gripper device can be combined as desired with the features of the above described embodiments. Each hoisting means is for instance driven by a separate drive, wherein a controller is configured to send both drives the same control signal for the purpose of raising or lowering the gripper, each drive comprising a motor with internal slippage or a slippage coupling such that in the hoisting mode a synchronous running of the hoisting means is automatically realized.
The length of the described moment arms are preferably determined by the redirecting means. This length is for instance determined by the form of the redirecting means and/or the position at which the redirecting means is connected to the rotation axis.
The gripper arm in the open end position is preferably rotated through more than 90 degrees relative to the closed end position, preferably more than 120 degrees, more preferably more than 150 degrees and most preferably about 180 degrees.
In a further preferred embodiment the redirecting means has a plurality of substantially straight sides, wherein in any case two sides have an unequal length. Because of the rotation of the redirecting means with the rotation axis of the gripper the path of the cable along the redirecting means changes, whereby the length of the moment arm changes.
The redirecting means has for instance substantially the form of a polygon, such as a triangle. The corners of the polygon are for instance rounded to some extent in order to prevent the redirecting means cutting into the cable.
The invention further relates to a hoisting device for a trash rake cleaner, comprising a first cable and a second cable which are each connected with their one outer end to a load carrier, such as a gripper, and which are each connected with their other outer end to respectively a first and second hoisting means for the purpose of raising and lowering the load carrier with the cables, characterized in that each hoisting means is driven by a separate drive, the hoisting device further comprising a controller connected to the drives for controlling the drives by transmitting a control signal with the controller, wherein the controller has a hoisting mode in which the controller is configured to send the same control signal to both drives for the purpose of raising or lowering the gripper, each drive comprising a motor with internal slippage or a slippage coupling such that in the hoisting mode a synchronous running of the hoisting means is automatically realized.
The same advantages and effects apply for this hoisting device as described above for the gripper device. Features of the above-mentioned gripper device can in particular be selectively combined with the hoisting device according to the invention. In such a combination another load carrier can also be applied instead of a gripper.
The invention also relates to a trash rake cleaner comprising the above described gripper device or hoisting device.
In addition, the invention relates to a method for raising, lowering, opening and closing a gripper for a trash rake cleaner as described above, the method comprising the steps of:
The same advantages and effects apply for the trash rake cleaner and the method according to the invention as described above for the gripper device and the hoisting device.
Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying figures.
Gripper device 2 (
Gripper 6 comprises a movable gripper arm 20 and a fixed gripper arm 22. Movable gripper arm 20 comprises a tilting arm 29 with an opening 24 (
The gripper comprises a frame 32 (
As shown in the figures, the distance between the cables is smaller close to redirecting rollers 34 than the distance between points of engagement 26, 28 of the cables on tilting arm 29.
In the closed end position (
In the opened end position (
When during raising or lowering of gripper arm 20 a greater force is exerted on cable 12 and on cable 18, this will then increase the moment of force so that the gripper arm is held in its open end position. If a greater force is exerted on cable 18 than on cable 12, this difference will then be compensated by the difference in the length of the corresponding moment arm. Before this difference in moment arm can be overcome, the equilibrium of forces will be restored by the slippage in electric motor 14 or a slippage coupling arranged here.
The control of gripper device 2 comprises a frequency control 36 (
The controller is switchable to a mode in which only motor 14 receives the control signal (
An example of the control of device 2 for cleaning a trash rake will be described hereinbelow. Gripper 6 is initially situated a certain distance above the trash rake with the gripper arm in the opened end position. The controller is switched to the mode as according to
The gripper device is preferably situated on a mobile carriage or other displaceable construction so that the whole gripper can be displaced to a waste collection location in order to there unload the scooped-up material by opening the gripper.
Gripper device 2 optionally comprises a detection system 40 for detection of a slack cable (
An alternative gripper device comprises gripper 106 (
Gripper 106 comprises a frame 132. Redirecting rollers 134 are provided (
In the shown embodiment redirecting means 127 takes the form of an isosceles triangle, the corner points which arc rounded. The redirecting means is mounted on the shaft close to one of its equal angles. It is noted that other shapes and/or mounting points are also possible according to the invention. In the shown embodiment the base of the isosceles triangle is shorter than the two sides of equal length.
In an opened end position movable gripper arm 120 and fixed gripper arm 122 are situated at an angle of about 180 degrees relative to each other (
If however the gripper is brought into the closed end position (
The invention is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following claims, within the scope of which many modifications can be envisaged. The invention can thus find application with gripper arms which are moved vertically, but also with gripper arms which operate to some extent at an angle.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011205 | Jul 2013 | NL | national |
| 2011212 | Jul 2013 | NL | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/NL2014/050499 | 7/22/2014 | WO | 00 |
