The present invention relates to plant for feeding timber boards to and through a single-board feeder in accordance with the preamble of Claim 1. The invention relates in particular to high-speed production plants, i.e. plants in which the boards are fed to different stations at high speeds.

The timber boards are normally transported in sawmills with their longitudinal axes transversal to the direction of conveyor belt movement. The boards are not distributed uniformly on the belts and the spacings between the boards can vary widely. However, it is desirable to be able to convey the boards in a uniform and regular array, for instance in conjunction with sorting and cross-laying the boards. The boards are advanced with the aid of so-called single-board feeders which grip boards stored temporarily in a buffer region and advance the boards one by one for further handling.

Because the general aim is to increase the rate of production and therewith the speed at which boards are transported through the plant, it is endeavoured to keep the buffer region upstream of the individual board feeder under control, so that the buffer region will neither be too large nor too small. An excessively large buffer region will result in various kinds of disturbances in operation. For instance, the boards will not remain in contact with the conveyor, but will be pressed up and lifted in the buffer region. If the buffer region is too small or when no boards are present in said region, the feeder will stop. Both instances will immediately result in an interruption in production. Because a high production rate is contingent on the continuous outfeed of boards downstream of the board feeder, the buffer region must be kept constantly full of boards above a given lowest level, wherein the feeder output rate V_ut, i.e. the number of boards that are fed out per unit of time multiplied by the width of the board, must be lower than the board feeding speed V_in upstream of the individual board feeder. The buffer region upstream of the board feeder can be said to form a magazine or storage facility and is thus necessary for single-board feeding.

By utilizing the irregular advancement pattern of the boards on the conveyor to the single-board feeder, with which single-board dispensing of up to three boards per second is possible in single-board feeding operations, the problem presented by the buffer region at high production rates has been solved by the invention, which prevents the buffer region from expanding or decreasing to a lowest level in an uncontrolled manner. This is achieved by virtue of the invention having the characteristic features set forth in the following Claims.

The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawing, in which the Figure is a schematic side view of a conveyor path on which timber boards are placed cross-wise in the vicinity of a single-board feeder.

The conveyor belt of the embodiment illustrated in Fig. 1 has the form of a belt conveyor 1 whose board-feeding rate is referenced V_in. The reference numeral 2 identifies a single-board feeder whose board-feeding rate is referenced V_ut. Thus, the conveyor 1 moves the boards 4 at the speed V_in, said boards lying cross-wise to the conveying direction. The boards 4 will not normally be distributed regularly on the conveyor 1, but may be spaced unevenly therealong. This is indicated on the left of the Figure. Since the single-board feeder 2 is intended to feed the boards one by one on a forwarding conveyor provided with dogging means, as indicated on the right of the Figure, it is necessary to obtain a given temporary storage or buffer 3 upstream of the single-board feeder. This buffer is obtained by ensuring that V_in is greater than V_ut, as earlier indicated. The aforedescribed forms part of the known technology and a more detailed description is thereof unnecessary.

The invention enables the buffer region 3 upstream of the single-board feeder 2 to be maintained within a controlled size. There is provided upstream of the single-board feeder 2 a regulator which includes endless belts 5 disposed across the width of the conveyor 1, each of said belts being guided over respective guide wheels or rollers 6, of which one is driven. The upper run of the endless belt 5 is located above the upper transporting plane of the conveyor 1 and will thus engage the timber boards 4. As indicated in the drawings, the upper run of the belt 5 shall move in the transporting direction of the conveyor 1. The speed of the belt 5 is V_reg, which is lower than the speed V_in of the conveyor 1. The unevenly distributed boards 4 transported on the conveyor 1 will either be gripped or retarded by the belt 5 as a result of the difference between the speeds V_in and V_reg. Thus, a pre-buffer 3' will be built-up with boards on the upper run of the belt 5 at the same time as the regulator device will deliver the boards that collect thereon in a delayed rate to the conveyor 1 upstream of the single-board feeder 2 when so required by the feeder buffer 3. The pre-buffer 3' can be allowed to grow or expand to a given extent upstream of the regulator. Thus, despite the boards being forwarded to the single-board feeder 2 on the conveyor 1 at the speed V_in, enlargement of the buffer region 3 upstream of the single-board feeder 2 will be equalized in accordance with the timing of the conveyor 1, i.e. an enlargement which keeps within largets and smallest permitted limits. Retardation of the boards and feeding of the boards to the single-board feeder 2 is made possible by utilizing the gaps between the boards on the conveyor 1 upstream of the regulator device. The invention thus enables building-up of the pre-buffer 3' and of the buffer 3 upstream of the single-board feeder 2 to be continued for given shorter periods, even if the feeder 2 is stopped due to a halt in production of the feeder, for instance. The regulator can be constructed to adapt to different speeds of the conveyor 1, and also to different board dimensions and feeder capacities. The regulator speed V_reg will normally lie between V_in and V_ut. The invention thus provides a highly flexible arrangement which can be installed in existing plants to solve an existing serious problem, particularly in the case of high-production plants. In principle, the conveyor belts may be of any appropriate kind and made from any suitable material, including high friction chains, provided that they will lower the rate of feed of the boards the speed V_reg.