EP0571343A1

EP0571343A1 - A sanding machine for wood panels

Info

Publication number: EP0571343A1
Application number: EP93830214A
Authority: EP
Inventors: Gino Botteghi
Original assignee: DMC SpA
Current assignee: DMC SpA
Priority date: 1992-05-21
Filing date: 1993-05-19
Publication date: 1993-11-24
Also published as: IT1257801B; ITBO920194A0; ITBO920194A1

Abstract

In a wide belt sander, the sanding head (1) is equipped with a battery of pneumatic actuators (7) supporting and operating a set of corresponding pads (6), each connected to and supplied with air by a pair of independent ducts (11, 12) maintained at different internal operating pressures (P1, P2); the operation of the actuators (7) is interlocked to a programmable controller (10) in such a way that the pressing force (F) applied to the abrasive belt (5) through the individual pads (6) can be adjusted selectively in response to the dimensions, geometry and physical properties of the panel (2) fed through the machine.

Description

The present invention relates to a wide belt sander for wood panels.
Machines of the type in question generally comprise an upright frame supporting a conveyor on which workpieces to be sanded (panels) are fed through in a longitudinal direction, and above the conveyor, sanding means disposed parallel to the conveying surface and consisting in an abrasive belt looped around a set of mutually parallel rollers of which the axes are disposed transversely to the conveyor. During operation, the abrasive belt is tensioned by the action of fluid power cylinders impinging on the rollers (a single machine obviously might be equipped with a number of sets of rollers carrying a succession of sanding belts arranged along the feed axis and supported by the one frame).
The typical machine further comprises a plurality of pressure elements acting on one portion of the abrasive belt loop, normally between two successive rollers positioned immediately above the conveying surface, each individually capable of directing the belt downwards toward the conveyor. The resulting battery of pressure elements compasses at least the full width of the conveyor, and is designed thus to afford a controlled sanding action by ensuring that the abrasive belt engages the entire surface of the work, even in the event that the panel may present rough patches or areas of dissimilar thickness.
Such pressure elements consist generally in a pad operated by an actuator, for example a pneumatic cylinder, and positioned to impinge on the abrasive belt. Naturally, the single machine will comprise several actuators and several pads disposed one alongside the other (the number of the actuator-pad assemblies variable according to the width of the abrasive belt and the transverse dimension of the conveyor) and functioning in the manner of piano keys, with each actuator-pad assembly activated by a relative control medium (for example, a solenoid valve activated in turn by a corresponding feeler installed preceding the pad in the feed direction) and invested with movement between a limit position substantially of operation, in which the pad rides in contact with the belt, and a limit position of deselection, distanced from the belt.
The actuator-pad assemblies are mounted to a cross member positioned above the abrasive belt, located between the tension rollers and in most instances arranged transversely with respect to the conveyor on which the panel is fed through. The cross member is secured in its turn to the frame of the machine. In practice, the sanding operation performed by a machine of this type commences as the panel, moving forward on the conveying surface, engages an array of feelers extending transversely across the feed path (each connected to a relative solenoid valve) and thus able to establish the width and length of the area to be sanded. The signals triggered by the feelers are directed into a central control unit and processed with reference to previously entered parameters, whereupon the unit pilots the descent and/or the ascent of the different actuator-pad assemblies (the pneumatic cylinder is generally a spring-returned single acting type) according to the information received, which as intimated above will reflect the proportions of the panel fed into the machine.
The control unit also measures the distance between the array of feelers and the cross member to which the actuator-pad assemblies are mounted, and thus can calculate the moment when the pad must respond, according to the rate of feed and the length of the panel. With this type of arrangement, the relative positioning of the actuators (hence of the abrasive belt) can be selected, again by way of the control unit, in such a manner as to ensure that panels do not emerge with particular defects, for example, rounded side edges. This is achieved conventionally by programming the control unit to lower (i.e. to activate) the entire battery of pads over the full transverse dimension of the panel, minus one pad or more on each side, and thus impinge on the working width of the abrasive belt according to the grade of finish required, to the dimensions, geometry and physical properties of the panel, naturally also to the experience acquired by the user of the machine in sanding and thicknessing generally, and to the nature of the surface.
The main drawback betrayed by wide belt sanders is precisely the difficulty in achieving a genuinely controlled, or at least selective sanding action, on especially delicate areas of a panel.
It will be clear that the solution outlined above is adversely affected by the intrinsic shortcomings of pneumatic systems, or in practical terms by the difficulty of modulating abrasive force to match a given finishing requirement, and the fact that fast response is not always achieved.
The object of the present invention is to eliminate the aforementioned difficulties by providing a wide belt sander equipped with a pneumatic system such as will allow the application of differentiated pressures through the actuator-and-pad assemblies, bringing the benefit of a selective sanding action commensurate with the finishing requirements for a given panel.
The stated object is realized in a wide belt sander as characterized in the appended claims.
The invention will now be described in detail, by way of example, with the aid of the accompanying drawings, in which:

fig 1 is a schematic representation of the sanding machine according to the invention, viewed in side elevation;
fig 2 is a detail of pneumatic means by which the pressure pads are operated in the machine of fig 1, viewed schematically in a front elevation;
figs 3 to 10 are schematic diagrams, seen in plan, showing certain possible sanding actions obtainable with a machine according to the invention.

Referring to the drawings, a wide belt sander for wood panels according to the invention comprises at least one sanding head 1, consisting in a set of mutually parallel rollers 3 (three rollers in the example of fig 1) positioned above and extending in transverse or longitudinal alignment with a flat conveyor 4 on which the panels 2 are fed through the machine, and a length of abrasive belt 5 looped around and tensioned by the rollers 3, and capable of movement parallel with or transversely to the conveyor 4 according to the finish required.
The sanding head 1 further comprises a plurality of pads 6 located between two of the three rollers 3, and more exactly those nearer to the conveyor 4, disposed one alongside the next along a direction parallel to the axes of the rollers 3 and engaged in sliding contact with the reverse face of the abrasive belt 5, i.e. the face opposite from that by which the panel 2 is sanded. Each such pad 6 is supported and actuated by one of a corresponding plurality of pneumatic elements 7, illustrated in the example of fig 2 as single acting cylinders 13, mounted to a cross member 8 affording a respective plurality of individual seatings and able thus to operate independently of one another. Accordingly, each single pad 6 can be directed by the relative cylinder 13 toward the conveyor 4 (in the activated or ON condition), applying a predetermined pressing force F, or distanced from the conveyor (deselected or OFF).
The single cylinders 13 are interlocked to relative sensing means 9 able to establish the dimensions of the panel 2 and pilot the operation of monitoring and control means 10 by which the air supply to the cylinders 13 is switched on and off.
The sensing means 9 in question might consist, by way of example, in a plurality of transducers 14 such as voltage dividers or potentiometers, arrayed parallel to and preceding the battery of pads 6 in the direction followed by the panel 2. The function of the transducers 14 is to intercept the panel 2 entering the machine and generate voltage signals proportional to the thickness and the horizontal dimensions encountered.
The outputs of the transducers 14 are connected to an analog-digital converter 15, connected in turn to one input of an electronic processor 16 of which the outputs control the air supply to the pneumatic cylinders 13. A second input of the processor 16 is connected to further transducers 17 (for example, analog or digital sensors) capable of measuring the distance travelled by the panel 2; accordingly, the cylinders 13 and the pads 6 can be operated both in response to the signals generated by the dimension transducers 14, and allowing for the difference in position between these same transducers 14 and the line of cylinders 13 as calculated by the distance transducers 17.
As discernible from fig 2, each of the cylinders 13 is connected to and able to receive compressed air from two independent ducts 11 and 12 of which the internal pressures, denoted respectively P1 and P2, are dissimilar. The ducts 11 and 12 are controlled by the electronic processor 10 in such a way as to allow of regulating the pressing force F applied by way of the cylinders 13 and pads 6 according to the dimensions, geometry and physical properties of the panel 2, on the basis of preset values programmed into the processor 16.
Each cylinder 13 is connected pneumatically to the ducts 11 and 12 by way of a pair of conventional valves 18a and 18b (illustrated by graphic symbols in fig 2) interposed between the ducts 11 and 12 and the cylinder 13 and constituting a part of the monitoring and control means 10. The valves 18a and 18b are also connected electrically to the output of the processor 16, which is programmed to respond to the input data received from the transducers by generating an activating signal P1 ON or P2 ON to connect the cylinder 13 to the relative duct 11 or 12, or a deactivating signal OFF which closes the valve 18a or 18b. A third signal might obviously be one that closes both valves 18a and 18b, leaving the cylinder 13 disconnected from the air supply altogether and vented to the atmosphere (as shown in fig 2).
To rationalize the construction of the machine and achieve greater compactness in design, one of the two ducts 11 and 12 might be incorporated directly into the cross member 8 (as indicated schematically in fig 1).
For certain types of sanding, one of the ducts 11 or 12 might also be depressurized completely (zero pressure denoted P0 in the drawings).
A machine structured in the manner thus described is able to produce a variety of sanding actions on panels 2 exhibiting particular types of surface, as illustrated by way of example in figs 3 to 10 where the arrow denoted F1 is the feed direction followed by the panel 2, and the arrow denoted F2 indicates the direction of movement of the abrasive belt 5; P1 denotes a pressure value lower than P2, whilst E denotes that the cylinder 13 is deselected, that is to say, not activated at all during the passage of the panel 2.
More exactly, figs 3 to 7 show an abrasive belt 5 running transversely to the feed direction of the panel 2 carried forward by the conveyor 4 (in such a way as to follow the grain of a natural wood, for example), whereas in fig 8 the abrasive belt 5 runs parallel with and against the feed direction.
In the case of figs 9 and 10 more particularly, the respective panels 2 exhibit edges B bearing traces of a hard bonding adhesive, and edges B1 projecting above the remaining surface area.
The machine disclosed operates thus: as a panel 2 fed in on the conveyor 4 is intercepted by the transducers 14, the signals generated are received by the electronic processor 16, which analyzes and compares the values with stored parameters (shape and dimensions, type of wood, special geometries if any), before applying the appropriate activating signal P1 ON or P2 ON to the valves 18a and 18b of the individual cylinders 13. Any cylinders 13 not required for the panel 2 in hand are deselected (E) by the processor 16, needless to say. Similarly, a cylinder 13 can be deactivated (P0) temporarily or momentarily during the pass by depressurizing the relative duct 11 or 12.
By virtue of the fact that two different pressures can be applied selectively via each of the single cylinders operating the pads, panels can be sanded with greater precision and a quality finish to the edges (clearly illustrated in figs 3...10), though without unduly upsetting either the architecture of the machine or its essential mode of operation.

Claims

1) A wide belt sanding machine for wood panels (2), comprising at least one sanding head (1) consisting in a plurality of mutually parallel rollers (3) disposed transversely to or parallel with and above a conveyor (4) on which panels (2) are fed through the machine, and an abrasive belt (5) looped around and tensioned by the rollers (3) and set in motion parallel with or transversely to the conveyor (4), also a plurality of pads (6) positioned between at least two adjacent rollers (3) located in close proximity to the conveyor (4), arranged one beside another along an axis parallel to the longitudinal axes of the rollers (3) and engaged in sliding contact with the face of the abrasive belt (5) opposite from the face offered to the panels (2), each associated with and actuated by one of a corresponding plurality of pneumatic elements (7) mounted to a cross member (8) and capable thus of mutually independent operation in such a way that the respective pads (6) can be directed closer (ON) to the conveyor (4), with a predetermined pressing force (F), and away (OFF) from the conveyor (4), wherein each pneumatic element (7) is interlocked to one of a corresponding plurality of means (9) capable of sensing the dimensions of the panel and piloting the operation of monitoring and control means (10) governing the compressed air supply to the pneumatic elements (7),
characterized
-in that the pneumatic elements (7) are connected individually to and supplied with compressed air from at least one pair of independent ducts (11, 12), each maintained at an internal pressure (P1, P2) different from that of the other, and operated by the monitoring and control means (10) in such a manner that the pressing force (F) applied by way of the pads (6) can be adjusted selectively and programmably in response to the dimensions, geometry and physical properties of the panel (2).

2) A machine as in claim 1, wherein one of the two ducts (11, 12) is incorporated directly into the cross member (8).

3) A machine as in claim 1, wherein each pneumatic element (7) is connected to the two ducts (11, 12) by way of valve means (18a, 18b) constituting a part of the monitoring and control means (10) and selectable in operation in such a way as to allow the activation (P1 ON, P2 ON) of the respective pneumatic element (7), resulting in movement of the pad (6) closer to the conveyor, or the deactivation or deselection (OFF) of the pneumatic element.

4) A machine as in claim 1, wherein sensing means (9) consist in a plurality of single transducers (14) corresponding in number to the pneumatic elements (7), arrayed parallel to and preceding the pads (6) in the feed direction followed by the panel (2) in such a manner as to intercept the incoming panel and generate respective output signals proportional in value to the thickness and the dimensions of the panel (2), for use by the monitoring and control means (10).

5) A machine as in claim 1, wherein monitoring and control means (10) consist substantially in an electronic processor (16) comprising first inputs connected to the sensing means (9) and outputs controlling the air supply to the ducts (11, 12), hence to the pneumatic elements, and second inputs connected to means (17) capable of measuring the distance travelled by the panel (2), in such a way that the pneumatic elements (7) can be activated both in response to the signals generated by the sensing means (9) and allowing for the difference in position between the sensing means (9) and the pads (6).

6) A machine as in claim 1, wherein the value of the pressure (P1, P2) registering internally of one of the ducts (11, 12) is equal to zero.