Control arrangements for hydraulically-operated wood particle or fiber board press

A device for use in hydraulically-operated press having a movable press table and at least one hydraulic cylinder for moving the press table, for controlling both the position and the speed of travel of the press table during at least part of the pressing cycle, said device comprising

• at least one actual-value transmitter that delivers a signal representing the actual position of the press table relative to a reference point,
• a set point transmitter that, at each point of time of said part of the pressing cycle, delivers a signal representing a desired position of the press table at the point of time in question,
• a first summation point connected to said at least one actual-value transmitter and to said set point transmitter to produce from the two signals a variance signal that represents the deviation of the actual value from the set point value, and
• a control means for the hydraulic cylinder responsive to the variance signal for correcting the deviation,
• said set point transmitter having means for setting a plurality of predetermined, arbitrary positions of the press table relative to the reference point,
• means for determining the length of travel of the press table from any one of said set positions to a subsequent one,
• means for settling a predetermined, arbitrary period of time, in which the press table is to be moved said length of travel,
• means for determining the speed of travel of the press table required for moving the press table said length of travel in said set period of time, and
• a ramp generator responsive to the speed of travel of the press table for delivering to said first summation point a signal indicative of the desired position of the press table at any moment during said period of time.

A device for use in a hydraulically-operated press having a movable press table and at least one hydraulic cylinder for moving the press table, for controlling the position and the speed of travel of the press table during a part of the pressing cycle and the hydraulic pressure in the cylinder as a function of press time during an other part of the pressing cycle, said device comprising

• at least one actual-value position transmitter that delivers a singnal representing the actual position of the press table relative to a reference point,
• an actual-value pressure transmitter that delivers a signal representing the actual hydraulic pressure in said one cylinder,
• a set point transmitter that on one hand, at each point of time of the first mentioned part of the pressing cycle, delivers a signal representing a desired position of the press table at the point of time in question and on the other hand, at each point of time of said other part of the pressing cycle, delivers a signal representing a desired hydraulic pressure at the point of time in question,
• at least one summation point connected to said at least one actual-value position transmitter, to said actual-value pressure transmitter and to said set point transmitter to produce from either of the actual-value signals and its associated set point signal a variance signal that represents the deviation of the actual value from the set point value, and
• a control means for the hydraulic cylinder responsive to the variance signal for correcting the deviation,
• said set point transmitter having a plurality of means, each one for setting a predetermined, arbitrary position of the press table relative to the reference point,
• means for determining the length of travel of the press table from any one of said set positions to a subsequent one,
• a plurality of means, each one for setting a predetermined, arbitrary period of time in which the press table is to be moved said length of travel,
• means for determining the speed of travel of the press table required for moving the press table said length of travel in said set period of time,
• a plurality of means, each one for setting a predetermined, arbitrary hydraullic pressure,
• means for determining the pressure change required for going from any one of said set pressures to a subsequent one,
• a plurality of means, each one for setting a predetermined, arbitrary, other period of time, in which the hydraulic pressure is to change from said one set pressure to said subsequent pressure,
• means for determining the pressure change rate required for going from said one set pressure to said subsequent pressure in said other set period of time, and
• a ramp generator on one hand responsive to the speed of travel of the press table for delivering to the summation point a signal indicative of the desired position of the press table at any moment during the first mentioned set period of time, and on the other hand responsive to the hydraulic pressure change rate for delivering to the summation point a signal indicative of the desired hydraulic pressure at any moment during the other set period of time, whereby the set point transmitter is programmable with a substantially arbitrary control curve.

A device for use in a hydraulically-operated press having a movable press table and at least one hydraulic cylinder for moving the press table, for controlling the hydraulic pressure in the cylinder as a function of press time during at least part of the pressing cycle, said device comprising at least one pressure transmitter that delivers a signal representing the actual hydraulic pressure in the hydraulic cylinder,

• a set point transmitter that, at each point of time of said part of the pressing cycle, delivers a signal representing a desired hydraulic pressure at the point of time in question,
• a summation point connected to said at least one pressure transmitter and to said set point transmitter to produce from the two signals a variance signal that represents the deviation of the actual value from the set point value, and
• a control means for the hydraulic cylinder responsive to the variance signal for correcting the deviation,
• said set point transmitter having means for setting a plurality of predetermined, arbitrary hydraulic pressures,
• means for determining the pressure change required for going from any one of said set pressures to a subsequent one,
• means for setting a predetermined, arbitrary period of time, in which the hydraulic pressure is to change from said one set pressure to said subsequent pressure,
• means for determining the pressure change rate required for going from said one set pressure to said subsequent pressure in said set period of time, and
• a ramp generator responsive to the hydraulic pressure change rate for delivering to the summation point a signal indicative of the desired hydraulic pressure at any moment during said period of time.