This invention relates generally to planers and infeed tables. More specifically, this invention relates to position and pressure control of planer and infeed table press rolls.
A planer provides a smooth finish on up to four sides of rough lumber that has been produced by a saw mill. Referring to FIG. 1, a typical high speed, high production planer 10 includes multiple press rolls 20. The press rolls 20 drive the wood through high speed blades, called xe2x80x9ccutter heads,xe2x80x9d which cut a smooth surface on the wood. These press rolls 20 must be accurately positioned in order to appropriately engage wood being fed into the planer 10. The press rolls 20 must also apply a significant amount of downward force on the wood passing underneath them to create the traction required to push the wood through the planer""s cutting heads.
A common way to provide positional and pressure control over the press rolls 20 is to use either a stacked hydraulic cylinder 30 or a jack screw and spring (not shown). These methods, however, do not provide position or force indication and require manual intervention when the roll 20 position or tension forces need to be adjusted. As a result, using these methods, the force exerted on the wood is difficult to accurately control and adjusting the pressure settings during operation is unreliable. In addition, these prior designs allow excessive forces to be experienced by the components in the press roll tower assembly 21 during operation, resulting in undue wear and premature failure of the roll tower 21 components.
The ideal function of an infeed table is to present a continuous ribbon (end to end) of wood into the planer 10. Referring to FIG. 2, a typical infeed table 110 also includes multiple press rolls 120. The center press rolls are arranged in a powered hold down 124. Referring to FIGS. 1 and 2, in operation, wood transitions horizontally into the deck area 126 of the infeed table 110, where it is grabbed by the first set of press rolls 122, called xe2x80x9cpineapple rolls,xe2x80x9d and directed lengthwise towards a planer entrance 12 (see FIG. 1). The feed rolls 120 on the table run faster than the press rolls 20 in the planer 10 to allow the wood to xe2x80x9cbutt upxe2x80x9d end to end before entering into the planer 10 through its entrance 12. Unfortunately, conventional infeed tables, such as infeed table 110, require operator intervention to adapt to various board thicknesses. Conventional infeed tables also lack a reliable way to control the position and pressure of the press rolls.
Referring to FIG. 3, a conventional hydraulic actuation system for modifying the position and pressure of the press roll 20 of FIG. 1 includes a double hydraulic cylinder 30 and various control components. Four way directional control valves 34 are provided for each cylinder. A flow control valve 37 and a dual pilot operated check valve 33 are mounted inline with the four way directional control valve 34 for the bottom cylinder. A pressure reducing valve 35 is mounted inline with the four way directional control valve for the top cylinder. An accumulator 32 and pump 39 are also provided. Fluid flow is directed between the bottom 38 and top 36 of each cylinder to control actuation of the press roll 20.
One aspect of the present invention is to enable a press roll assembly that provides reliable control over press roll position and pressure.
Another aspect of the present invention is to enable a press roll assembly that automatically adapts to various board thicknesses.
According to the foregoing aspects of the present invention, a press roll assembly includes a press roll adapted to exert a pressure on wood passing through a device, such as a planer or an infeed table. A controller is configured to control a position of the press roll and the pressure exerted by the press roll. A position sensor senses the position of the press roll and transmits a signal corresponding to that position to the controller. A pressure sensor measures the pressure being exerted by the press roll and transmits a signal corresponding to that pressure to the controller. A press roll actuator, preferably comprising a single hydraulic cylinder and hydraulic servo valve, can also be provided to move the press roll based on electrical signals from the controller. The press roll assembly of this invention can be automated to automatically adjust the position of the press roll and the pressure exerted by the press roll on wood. A planer or infeed table preferably comprises a plurality of these press roll assemblies, wherein each of the press roll assemblies can be independently controllable.
A method of automatically controlling a position and pressure of a press roll is provided by another aspect of this invention. The position of the press roll is sensed and the position can then be automatically and dynamically adjusted toward a desired position. The desired position can be based on user-defined set points. The desired position can also be automatically determined based on sensed board thickness. Similarly, the pressure being exerted by the press roll is sensed and the pressure can then be automatically and dynamically adjusted toward a desired pressure.
Upgrading an existing device, such as a planer or infeed table, to provide automatic control of press roll position and pressure is accomplished by retrofitting the existing device with a force and position controller. A position sensor is also provided to measure the position of the press roll and to communicate the position of the press roll to the controller. A pressure sensor is provided to measure the pressure exerted by the press roll on wood travelling through the device and to communicate the measured pressure to the controller. A communications interface is provided to permit communication between the controller and existing circuitry. The existing circuitry, for example, could be a Programmable Logic Controller (PLC) and an Operator Interface, including both a Human Machine Interface (HMI) and switches.
Once configured, the force and position controller can control the position and pressure of the press roll based on signals received from the position and pressure sensors. Pressure and position adjustment of the press rolls can be accomplished, for instance, through use of an actuator that adjusts the position and pressure of the press roll based on controller signals. In a preferred embodiment, the actuator comprises a single hydraulic cylinder and a servo valve, wherein the servo valve is arranged in electrical communication with the controller. dr
The foregoing objects, features, and advantages of the present invention will become more readily apparent from the following detailed descriptions of various preferred embodiments, made with reference to the following figures, in which:
FIG. 1 is a side elevation view, with cutaways, of a planer according to the prior art.
FIG. 1A is a side elevation view, with cutaways, of a planer according to one aspect of the invention.
FIG. 1B is an enlarged perspective view of a hydraulic cylinder attached to a press roll for adjusting the position and pressure of the press roll.
FIG. 2 is a side elevation view of an infeed table according to the prior art.
FIG. 2A is a side elevation view of an infeed table according to another aspect of this invention.
FIG. 3 is a somewhat schematic illustration of an actuation system for adjusting a position of and pressure exerted by a press roll according to the prior art.
FIG. 3A is a somewhat schematic illustration of an actuation system for adjusting a position and pressure exerted by a press roll according to yet another aspect of this invention.
FIG. 4 is a block diagram of an electrical control system for the planer of FIG. 1A according to a further aspect of this invention.
FIG. 5 is a block diagram of an electrical control system for the infeed table of FIG. 2A according to a still further aspect of this invention.