Method and apparatus for regulating mold clamping force in an injection molding machine
First Claim
1. A method for regulating the clamping force in an hydraulic clamp cylinder of an injection molding machine, wherein a flow control valve is provided to control the flow of pressurized hydraulic fluid from a pump to the clamp cylinder, said method comprising:
- (a) providing a clamping force set point value corresponding with a desired clamping force to be provided by a clamp hydraulic cylinder during a clamp force maintenance portion of a clamp operating cycle;
(b) determining a desired clamp cylinder hydraulic pressure value corresponding with the desired clamping force value;
(c) sensing actual hydraulic pressure in the hydraulic clamp cylinder during a first clamp operating cycle to provide an actual clamp cylinder hydraulic pressure during the clamp force maintenance portion of the clamp operating cycle;
(d) comparing the actual clamp cylinder hydraulic pressure with the desired clamp cylinder hydraulic pressure to provide a signal representative of the actual pressure difference between the actual and the desired pressures; and
(e) during the next succeeding clamp operating cycle, controlling the time of closing of the flow control valve connected with the clamp hydraulic cylinder, relative to the time of closing of the flow control valve during the preceding clamp operating cycle, by adding at least a part of the actual pressure difference in the preceding cycle to the pressure value sensed during the preceding cycle while the clamp was in the clamp force maintenance portion of the clamp operating cycle to provide a control signal to close the flow control valve at a time in the clamp operating cycle to provide a clamping force that is closer to the desired clamping force.
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Accused Products
Abstract
A method and apparatus for controlling the hydraulic pressure in an hydraulic clamping cylinder to correspond with a desired clamping force and to compensate for overshoot of the hydraulic pressure caused by time delays in operating the components in the hydraulic circuit. The control arrangement involves the sensing of the actual hydraulic pressure during the clamp force maintenance portion of a clamping cycle and comparing the actual pressure with a desired pressure to provide a correction signal to be utilized to control the operation of the hydraulic system during the next succeeding cycle so that the actual hydraulic pressure during the clamp maintenance portion of the clamping cycle during the next succeeding cycle results in a clamping force that is closer to the desired clamping force.
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Citations
10 Claims
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1. A method for regulating the clamping force in an hydraulic clamp cylinder of an injection molding machine, wherein a flow control valve is provided to control the flow of pressurized hydraulic fluid from a pump to the clamp cylinder, said method comprising:
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(a) providing a clamping force set point value corresponding with a desired clamping force to be provided by a clamp hydraulic cylinder during a clamp force maintenance portion of a clamp operating cycle; (b) determining a desired clamp cylinder hydraulic pressure value corresponding with the desired clamping force value; (c) sensing actual hydraulic pressure in the hydraulic clamp cylinder during a first clamp operating cycle to provide an actual clamp cylinder hydraulic pressure during the clamp force maintenance portion of the clamp operating cycle; (d) comparing the actual clamp cylinder hydraulic pressure with the desired clamp cylinder hydraulic pressure to provide a signal representative of the actual pressure difference between the actual and the desired pressures; and (e) during the next succeeding clamp operating cycle, controlling the time of closing of the flow control valve connected with the clamp hydraulic cylinder, relative to the time of closing of the flow control valve during the preceding clamp operating cycle, by adding at least a part of the actual pressure difference in the preceding cycle to the pressure value sensed during the preceding cycle while the clamp was in the clamp force maintenance portion of the clamp operating cycle to provide a control signal to close the flow control valve at a time in the clamp operating cycle to provide a clamping force that is closer to the desired clamping force. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An injection molding machine including an hydraulic clamp cylinder and piston for applying and maintaining a clamping force on a separable mold to maintain the mold in a closed condition, said apparatus comprising:
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(a) pressurizing means for providing hydraulic fluid under pressure to a clamp cylinder; (b) valve means positioned between the pressurizing means and the clamp cylinder, the valve means operable selectively between an open position to permit flow of pressurized hydraulic fluid from the pressurizing means to the clamp cylinder and a closed position to prevent flow of hydraulic fluid from the clamp cylinder to maintain hydraulic fluid under pressure within the clamp cylinder; (c) set point setting means for selecting and providing a predetermined set point clamping force value; (d) pressure transducer means in communication with the clamp cylinder for providing an output signal representative of the hydraulic fluid pressure within the clamp cylinder; (e) comparator means connected with the pressure transducer means and with the set point setting means for comparing the output signal of the pressure transducer means during a clamp force maintenance portion of a clamp operating cycle with the selected set point clamping force value to provide a correction signal representative of the actual pressure difference between the clamping force corresponding with the transducer output signal and the set point clamping force value; and (f) control means connected with the comparator means and with the valve means to provide a control signal for regulating the opening and closing of the valve means during a next succeeding clamp operating cycle to provide a clamping force during the clamp force maintenance portion of that next succeeding cycle that is closer to the set point clamping force value than was the clamping force in the immediately preceding clamp operating cycle. - View Dependent Claims (9, 10)
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Specification