US3845269A

US3845269A - Adjustable timing device

Info

Publication number: US3845269A
Application number: US00363364A
Authority: US
Inventors: R Bradley
Original assignee: USM Corp
Current assignee: USM Corp
Priority date: 1973-05-24
Filing date: 1973-05-24
Publication date: 1974-10-29
Anticipated expiration: 1991-10-29
Also published as: CA1012231A

Abstract

In a device for adjustably timing a machine function, a preset time for the machine function is continually adjusted in response to the machine function and the time preset. A preferred embodiment has means for varying the preset time and a successively initiated but independently operated additional timing device. The preferred embodiment also has means protecting the device from an overload of the machine-function-responsive adjustment to the preset time. The preferred embodiment is intended to time the operating cycle of an integrated cavity, high frequency machine.

Description

United States Patent 11 1 1111 3,845,269 Bradley Oct. 29, 1974 [54] ADJUSTABLE TIMING DEVICE 3,745,293 7 1973 Seyfried 219 1075 Inventor: Robert w y Marblehead 3,746,825 7/1973 Pfaffman 219/10.77

Mass Primary ExaminerBruce A. Reynolds [73] Assignee: USM Corporation, Boston, Mass. At ney, Ag or FirmRa|Ph g; Vincent [22] Filed: y 1973 A. White, Richard B. Megley [21] Appl. No.: 363,364 [57] ABSTRACT In a device for adjustably timing a machine function, a [52] Cl 219/1057, 219/1057 219/1031 preset time for the machine function is continually ad- 51 Int. Cl. H05b 5/04 iusted Fesponse the machine function and the [58] Field of Search 219/1057 10.61 10.75 time Preset A Preferred embdimem has means for 219/1O 77 1081 1055 varying the preset time and a successively initiated but independently operated additional timing device. The [56] References Cited preferred embodiment also has means protecting the device from an overload of the machine-function- UNITED STATES PATENTS responsive adjustment to the preset time. The pre- 2,429,819 10/1947 Jordan 219/10.77 ferred embodiment is intended to i the Operating cycle of an integrated cavity, high frequency machine. 3,742I180 4/1973 Bradley 219/10.8l 2 Claims, 2 Drawing Figures sum 3.845269 PATENYEUBUZ SHEET 1 a: 2 i

BACKGROUND OF THE INVENTION This invention relates to a device for adjustably timing a machine function.

Modern machines include many devices for automatically controlling machine operation. Such automatic controls increase the quality of machine operation by eliminating the variable response of an operator and the productivity of machine operation by freeing an operator for other duties. In addition, the operating times of some machine functions are so short as to make manual control of these machine functions difficult or impossible.

One of the many such modern machines is a high frequency heating machine. These machines apply high frequency electric energy to a workpiece to heat the workpiece material throughout the material. Such machines find utility, for example, in the heat drying of newly manufactured paper as well as the processing of many elastomeric materials. In the former example, the paper changes only in moisture content but not necessarily in appearance, making manual adjustment of such a heating device difficult as well as requiring the continual attention of an operator In addition, the speed at which a web of paper progresses from paper manufacturing machines leaves a particular portion of the web in the drying machine for such a short time as to make adjustment of the heating of that portion difficult. In the latter example, a process generally known as flow molding may be carried out by high frequency heat softening the elastomers while pressing the elastomers with a die to mold the elastomers into conformity with the die. Because the elastomer is engaged with a die during the high frequency process, it is difficult for an operator to observe the processing of the material. Variations in the size or composition of the workpiece material may additionally require adjustment of the high frequency machine. All these adjustments are required within a molding time which typically ranges from to seconds. Such short operating times again inhibit manual adjustment of the machine.

A machine particularly useful for performing the high frequency flow molding process on elastomeric workpieces is described in copending US. Pat. application Ser. No. 147,083, filed May 26, I971, and which issued as US Pat. No. 3,742,180 on June 26, 1973 in the name of R. W. Bradley. This machine has means defining a cavity for containing an electric field which means also enclose platens for applying the electric field and pressure to a workpiece placed between the platens. The cavity defining means also forms an electrically resonant circuit cooperative with a high frequency power supply to form a generator of the high frequency energy. Since the cavity defining means serves both as part of the electric field containing and applying means and as part of the electric field generating means, such a machine may be described as an integrated cavity, high frequency machine.

One property of the machine described in the above recited patent application is to supply a substantially constant electric field power per unit area of workpiece material for workpieces of various areas. While this property of the machine extends for changes in workpiece area in excess of 200 percent, for very large changes in workpiece area, the machine exhibits a slightly nonlinear relationship of field power per unit area to the area of a workpiece. For this and other reasons it has been empirically determined that the time for a flow molding process of a small workpiece of material otherwise similar to a larger workpiece should be reduced slightly from that for the larger workpiece.

SUMMARY OF THE INVENTION Accordingly it is an object of the invention to provide a device for adjustably timing a machine function responsive to the functioning of the machine and to a time preset into the-device.

To this end the invention provides a device for adjustably timing a machine function. The device is preset to time a machine function from its inception to the end of the present time; preferably, the time preset is variable. Means responsive to the expiration of the present time preferably terminates the machine function. The preset time period is adjusted in response to the machine function and the preset time. In a preferred embodiment a successively initiated but independently operating timing device is also provided. The preferred embodiment also has means protecting the device from an overload of the machine-functionresponsive adjustment to the preset time. The preferred embodiment is particularly useful with a high frequency, integrated cavity machine.

DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an operative portion of an integrated cavity, high frequency machine of the type described in further detail in the above recited patent application. The machine has means defining a cavity comprising a box-like structure 10 having an open side and a cover 12 cooperatively engageable with the structure for closing the open side of the structure. The cover is mounted on a double acting linear motor 14 for movement toward and away from the structure. Means (not shown) within the structure 10 support a platen 16 while another platen 18 is connected to the cover for movement therewith. A workpiece 20 disposed between the platens is pressed between the platens when the cover closingly engages the structure. The structure l0 and cover 12 cooperate to form a cavity electrically resonant at a desired high frequency. Appropriate electric connections are made from the platens, structure and cover to a high frequency power supply (not shown) by electrical leads 22. The cavity electrically cooperates with the high frequency power supply to form a high frequency generator. The structure 10 and cover 12 additionally cooperate to contain the generated high frequency electric energy in the machine.

FIG. 2 shows a schematic of a control for the machine shown in FIG. 1 including a preferred embodiment of the adjustable timing device. A switch 24 is closed to complete a path across the power supply through relay 100. Relay 100 closes contacts 101 to supply power from a transformer generally at 26 to the adjustable timing device portion of the schematic generally at 28 through the bus 30. Relay 100 also closes contacts 102 to complete a circuit across the power supply through relay 200. Relay 200 closes contacts 201 to apply an operating voltage to a high frequency power supply tube 32. The tube 32 communicates with the electrically resonant cavity shown in FIG. 1 through leads 22. Accordingly, the tube begins to oscillate to provide high frequency energy simultaneously with the supply of power to the adjustable timing device through bus 30.

Current from the bus 30 begins to charge capacitor 34 through some later described intermediate resistors. When the charge on capacitor 34 produces a particular voltage relative to the voltage between resistors 35, a connected programmable unijunction transistor 36 (PUT) is caused to conduct. PUT 36 then produces a voltage at its base determined by grounding resistor 38; this voltage is provided to a connected siliconcontrolled rectifier 40 (SCR). The SCR 40 then begins to carry current from the bus 30 through relay 300 to ground. Current through relay 300 opens normally closed contacts 301 to open the circuit through relay 200. The contacts 201 of relay 200 then open to terminate operation of tube 32. As thus described, the timing device generally at 28 functions as a timer for operation of the high frequency generator from its inception to the end of a timed period, the timed period of operation being determined by charge accumulation on capacitor 34.

Charge accumulation on capacitor 34 is determined by current limiting

resistors

42, 44 and 46 between capacitor 34 and the supply bus 30. Resistor 42 is of fixed value series added to resistor 44 which is adjustable to variably preset a timing charge rate for the capacitor 34. Adjustment of resistor 44 thus permits presetting of a time period during which capacitor 34 will reach a voltage sufficient to trigger PUT 36.

A portion of the resistor 46 between an adjustable center tap 48 which is connected to the resistor 44 and the bus 30 further limits the current. However, the resistor 46 is connected across another resistor 50 which is connected between a cathode of tube 32 and ground. The cathode current of the tube 32 then produces a voltage across the resistor 50 opposed to that on the bus 30 and proportional to the cathode current of the tube. The voltage across the resistor 46 is thus also reduced in proportion to the cathode current of the tube. For any particular voltage applied to a plate of the tube 32, the plate to cathode current is proportional to the power of the tube. Leads 22 provide the high frequency power of tube 32 to the machine shown in FIG. 1. As further described above with particular reference to the recited patent application, the high frequency power provided by an integrated cavity machine of the type shown in FIG. 1 and described in the patent application is substantially proportional to the area of a workpiece in the machine. Accordingly, the current through the tube 32 varies in relation to the area of a workpiece in the machine. The voltage across resistor 46 is then also changed by the workpiece-arearesponsive functioning of the machine. Since the resistor 46 in part controls the charge accumulation on ca pacitor 34, the time for appropriate charge accumulation on the capacitor, already variably preset by resistor 44, is continually further adjusted by the high frequency machine function. Even without tube current, current through the resistor 46 to the center tap 48 additionally determines, in part, the time for appropriate charge accumulation on the capacitor 34 as preset by resistor 44. Thus, the time for charge accumulation on the capacitor 34 preset by resistor 44 is also further adjusted in response to the preset time.

In a specific example, the resistor 44 is first adjusted to a value which presets a time for accumulation of sufficient charge on the capacitor 34 to provide a voltage sufficient to trigger conduction of PUT 36. Activation of switch 24 begins charge accumulation on the capacitor 34 and the simultaneously activated high frequency machine function from their inception to the end of the present time determined by discharge of capacitor 34 through the PUT. The time preset by adjustment of resistor 44 is further adjusted or compensated by the high frequency function of the machine with resistor 46; the voltage drop across and hence the current through this resistor being responsive to the high frequency power provided in the machine. For example, if the machine provides to a larger workpiece a high frequency power producing a tube current providing 2 volts d.c. between the bus 30 and center tap 48 of resistor 46, a smaller workpiece producing a smaller high frequency power in the machine produces a smaller dc. voltage between the bus and center tap. The smaller the tube induced back voltage across the resistor 46, the greater the voltage drop from the bus to the center tap and the greater the current to capacitor 34. The greater the current to t the capacitor, the faster the charge buildup and the shorter the time to a voltage sufficient to trigger PUT 36. Also in example, if the adjustment or compensation from resistor 46 to a time preset at 15 seconds by the resistor 44 is 2.5 seconds, adjustment of resistor 44 to provide a preset 7.5 second time will reduce the adjustment or compensation to the preset time to 1.2 seconds; a linear relationship of this further adjustment exists. The preset time is thus also further adjusted by the time preset.

To facilitate operation of the timing device generally at 28, a capacitor 52 is provided between the PUT 36 and SCR 40. Capacitor 52 removes any transients from the voltage to the SCR which might prematurely trigger the SCR; it also sustains the triggering voltage to maintain conduction of the SCR for a time sufficient to permit operation of the relay 300. Relay 300 additionally closes normally open contacts 302 to insure complete discharge of capacitor 34 after each time it triggers PUT 36. Completely discharging the capacitor 34 assures accurate timing by starting the capacitor 34 from ground potential for each timing operation.

Convenient determination of the operation of the circuit may be made across checking ports 54. If the high frequency machine is operated otherwise than by the control shown in FIG. 2, the voltage measured across the ports 54 will be that which reduces the voltage from the bus 30 to the center tap 48 during operation of the timing device. On the other hand, if the ports 54 are shorted and the schematically shown circuit activated without operation of the high frequency machine the time preset by resistor 44 may be adjusted without further adjustment or compensation from the machine function or the time preset. For such testing and setup, separate means (not shown) for independently closing

contacts

101 and 201 may be provided.

A further portion generally at 56 of schematic FIG. 2 is a successively initiated but independently operated additional timing device. Conduction of the SCR 40 closes a circuit through this portion from the bus 30 to ground. Accordingly, operation of the portion generally at 56 is successive to that of the timing device generally at 28. Of course, continued operation of the portion generally at 56 is also dependent upon continued conduction of the SCR 40. Capacitor 52 maintains conduction of SCR 40 for this additional purpose.

The timing device of the schematic portion generally at 56 is generally similar to the timing device already described but without the further adjustment functions. Conduction by the SCR 40 permits current flow from the bus 30 through an adjustable resistor 58 to charge a capacitor 60. When the charge on the capacitor 60 produces a sufficient voltage, a PUT 62 connected to the capacitor is triggered into conduction. Conduction of PUT 62 through a resistor 64 provides a voltage which triggers an SCR 66 into conduction. Conduction through the SCR 66 carries current through a relay 400. Relay 400 then opens normally closed contacts 401 to terminate operation of the machine. Relay 400 also closes normally open contacts 402 to assure complete discharge of timing capacitor 60 for accurate timing. Adjustment of the resistor 58 adjusts the current flow to capacitor 60 to adjust the timing of the device. Since resistor 58 is independent of other portions of the schematic, operation of the timing device is independent of other portions of the schematic.

In the preferred operation of the device with the high frequency machine of FIG. 1, the high frequency power supply voltage required by the tube 32 is substantially in excess of the voltages required for the operation of other normal components of the type illustrated in schematic FIG. 2. To protect an operator and the device from an unexpected shorting of this higher voltage or other unexpectedly high voltages across the tube 32, an overload protection device generally at 68 is also provided. For this purpose a portion of the voltage from the cathode 32 is sampled by a potential dividing resistor 70. The sample voltage is applied to a zenner diode 72. In normal operation, the zenner diode 72 blocks this voltage from remaining portions of the schematic. However, should the voltage applied to the zenner 72 exceed its breakdown voltage, zenner 72 will then conduct to apply the voltage to SCR 40. The SCR 40 will then conduct to produce current through relay 300 opening normally closed contacts 301. Relay 200 is then disabled to open contacts 201 to immediately cut off the high frequency portion of the machine. A further zenner diode 74 is provided between the zenner diode 72 and ground. If the voltage carried through the diode 72 exceeds the breakdown voltage of the zenner diode 74, the zenner diode 74 will break down to immediately conduct the voltage to ground. To insure conduction of the SC R 40 to terminate high frequency operation, the breakdown voltage of zenner 74 should somewhat exceed that of zenner 72.

To complete description of schematic FIG. 2, certain additional components will be briefly described. Normally open contacts 103 are closed by initiation of current through relay 100 by switch 24 to latch relay 100 into current carrying condition. Thus, switch 24 need be only momentarily closed to initiate-automatic operation of the machine. Relay 100 additionally closes normally open contacts 104 to close a current path through relay 500. Relay 500 closes contacts (not shown) which operate the linear motor 14 to close the cavity defining means and to press a workpiece between the platens. Should the pressure applied by the linear motor 14 exceed that desired, a pressure overload switch (not shown) may open normally closed contacts 76; the path through relay 500 is then opened to terminate operation of the motor 14. Similarly, an emergency stop switch (not shown) may open normally closed contacts 78 to similarly terminate operation of the motor 14. Finally, the power supply for the bus 30 may be provided with rectifying diodes generally at 80 and a smoothing filter generally at 82.

Although the preferred embodiment has been described with reference to a high frequency machine, it should be understood that the preferred and other embodiments are operable with other machines. A current responsive to a function of such other machines may be introduced to resistor 50 or a voltage responsive to such machine functions introduced in place of resistor 50. As but one of many possible examples, a device responsive to the position of a movable member to provide a position-responsive current or voltage may be introduced.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. In a system for applying a high frequency electric field in an integrated cavity machine, for heating dielectric materials in which the intensity of the electric field is responsive to the size of the workpiece, a timing circuit comprising;

A. a high frequency electrical power source;

B. switching means connected to the power source to de-energize said source after a predetermined time;

C. capacitor timing means connected to the switching means to activate said switching means after said capacitor is charged to a predetermined voltage;

D. at least one variable resistor connected to the capacitor timing means for adjusting the charging current thereof to provide a predetermined charging period; and

E. Means connected to the variable resistor for adjusting the current flowing therein in response to the intensity of the electric field.

2. In a system for applying a high frequency electric field to a workpiece in which the intensity of the electric field varies with the size of the workpiece, a timing circuit as described in claim 1 wherein the power source is comprised of a high frequency vacuum tube excited by a rectified alternating current supply and the means for adjusting the current through the variable resistor comprises at least one dropping resistor connected to the cathode of the power supply tube such that the voltage drop across said dropping resistor is proportional to the current flowing in said cathode.

Claims

1. In a system for applying a high frequency electric field in an integrated cavity machine, for heating dielectric matErials in which the intensity of the electric field is responsive to the size of the workpiece, a timing circuit comprising; A. a high frequency electrical power source; B. switching means connected to the power source to de-energize said source after a predetermined time; C. capacitor timing means connected to the switching means to activate said switching means after said capacitor is charged to a predetermined voltage; D. at least one variable resistor connected to the capacitor timing means for adjusting the charging current thereof to provide a predetermined charging period; and E. Means connected to the variable resistor for adjusting the current flowing therein in response to the intensity of the electric field.