US3552184A - Post shock control system - Google Patents

Abstract

THE PRESENT INVENTION IS AN IMPROVEMENT IN SHOCK TESTING MACHINES OF THE TYPE THAT INCLUDE A CARRIAGE, AN ANVIL, AND MEANS FOR RAISING, HOLDING, AND RELEASING THE CARRIAGE AND BRAKING IT ON REBOUND. IN THE MACHINE DISCLOSED THE CARRIAGE IS FIRST RAISED TO AN ELEVATED POSITION, THEN CHARGED IN SUCH MANNER AS TO DETERMINE THE DEGREE OF IMPACT ON A FIXED ANVIL, THE CARRIAGE BEHIND HELD BY A PNEUMATIC BRAKE AS IT IS CHARGED. FINALLY THE CARRIAGE IS RELEASED SO THAT IT IMPACTS THE ANVIL, DEVELOPING A SHOCK PULSE, AND REBOUNDS, THE REBOUNDING BEING TERMINATED BY REAPPLICATION OF THE BRAKE. THE PRESENT INVENTION PROVIDES AN IMPROVEMENT COMPRISING VALVING AND CIRCUITRY SO ARRANGED THAT THE CARRIAGE IS HELD IN FULLY ELEVATED POSITION BY THE APPLICATION OF PNEUMATIC LINE PRESSURE TO THE BRAKE, BUT REBOUND IS TERMINATED BY THE APPLICATION OF A LESSER AND REGULATED PRESSURE TO THE BRAKE.

Description

Jan. 5, 1971 c. F. BREESE ETAL 3,552,184

' POST snocK CONTROL SYSTEM Filed Sept. 5, 1968 4 '2 Sheets-Sheet 1 7O 7 l4 IO HIGH PRESSURE I 1; 4 INVENTORS.

CHARLES E BREESE BY J. R. LEACH In 7Y1.

ATTORNEYS.

CARROLL R. ROBERTS- Jan. 5, 1971 Q BREESE EI'AL 3,552,184

POST SHOCK CONTROL SYSTEM Filed Sept. 5, 1968 2 Sheets-Sheet 2 ||ov A.C.

KIT

INVENTORS. CHARLES E BREESE J. R. LEACH CARROLL RI ROBERTS ATTORNEYS.

United States Patent 3,552,184 POST SHOCK CONTROL SYSTEM Charles F. Breese, Owasso, and J. R. Leach and Carroll R. Roberts, Tulsa, Okla., assignors to Avco Corporation, Tulsa, Okla., a corporation of Delaware Filed Sept. 3, 1968, Ser. No. 756,980

Int. Cl. G01n 3/08 US. CI. 73-12 6 Claims ABSTRACT OF THE DISCLOSURE The present invention is an improvement in shock testing machines of the type that include a carriage, an anvil, and means for raising, holding, and releasing the carriage and braking it on rebound. In the machine disclosed the carriage is first raised to an elevated position, then charged in such manner as to determine the degree of impact on a fixed anvil, the carriage being held by a pneumatic brake as it is charged. Finally the carriage is released so that it impacts the anvil, developing a shock pulse, and rebounds, the rebounding being terminated by reapplication of the brake. The present invention provides an improvement comprising valving and circuitry so arranged that the carriage is held in fully elevated position by the application of pneumatic line pressure to the brake, but rebound is terminated by the application of a lesser and regulated pressure to the brake.

BRIEF SUMMARY OF THE INVENTION The present invention comprises a brake control system for shock testing machines. The invention is an improvement over those shown in the following United States patents: 2,955,456, Jensen et al., Oct. 11, 1960'; 3,103,116, Kohli, Sept. 10, 1963.

The above patents describe a free fall shock testing machine in which a shock pulse is produced by impacting a free falling carriage, bearing a test specimen, against a fixed anvil. A shock absorbing element which is disposed on the anvil determines the shape of the resultant shock pulse. As indicated in the Kohli patent, a half sine wave pulse is ideally produced through the use of a resilient rubber pad.

The Kohli invention represents an improvement in reducing the tendency of the carriage to rebound one or more times after the initial impact and to produce multiple shock pulses. However, the Kohli solution involves the instantaneous application of full braking force to the rebounding carriage element. This is accomplished by the introduction of air into a chamber containing a braking sleeve or core. A pneumatic delay element is interposed between the air supply means and this chamber, for the purpose of delaying the braking action until after impact. While this delay means inherently provides a gradual build-up of air pressure in the aforesaid chamber, the gradation is sharp and uncontrolled. That is to say, the Kohli patent is largely concerned with the instant application of braking force to the bra-king element.

It should be noted that in the Kohli patent the same air pressure is utilized for holding the carriage in an elevated position, before the testing occurs, and for the prevention of multiple rebounding, after testing. The significance of this is that the full air supply pressure is there applied to the braking element for the prevention of multiple rebounding. As a consequence, the shape of the shock wave is improved but its oscillating characteristics are not entirely eliminated. The gradual buildup of air pressure referred to above tends to enhance the improvement. Nonetheless, the braking action is so abrupt as to indicate the need for further improvement.

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This is readily demonstrated by reference to the curve in FIG. 2 below, this curve being a graph of shock wave amplitude versus time on a framework of Cartesian coordinates, amplitudes of the shock wave being shown as ordinates and time instants as abscissae. FIG. 3 illustrates the corresponding form which characterizes the present invention. The elimination of the hunting is selfapparent.

The principal object of the present invention is to provide a post shock control system which automatically utilizes full pneumatic braking force for pre-test suspension and less than full pneumatic braking force for posttest arrest.

Another object of the invention is to provide a post shock control system in which the rebound braking force is relatively independent of the supply pressure and may be adjusted at the will of an operator.

DETAILED DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following description of the accompanying drawings, in which:

FIG. 1 is a schematic drawing showing an improved braking system for a shock testing machine in accordance with the present invention, this braking system including the pneumatic circuitry and valving and regulating arrangements;

FIGS. 2 and 3 are performance curves showing respectively the amplitude versus time characteristic of the prior art and the improved characteristic of the present invention;

FIG. 4 is an elevational sectional view, generally schematic, showing the details of the valve immediately associated with the brake of the FIG. 1 embodiment; and

FIG. 5 is a diagram of a preferred form of electrical circuit used in the FIG. 1 embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now specifically to FIG. 1, there is represented, in gross outline, a shock testing machine embodying a brake control mechanism in accordance with the invention. This shock testing machine comprises a carriage 6, secured to the upper end of a piston rod 7. A piston 8 is secured to the lower end of rod 7. The piston is reciprocally movable Within a suitably formed housing 9, shown generally in outline form. The housing is cylindrical, centrally apertured to receive the piston rod 7 and suitably shaped in its upper portion to define a cylindrical compartment 60, which contains a brake core 61. Additionally, said upper portion is formed to define an annular compartment 62 which is in communication with an air inlet 14. A brake per se is shown in detail in the above referenced Kohli patent, so that further detailed description of the brake per se is not required, the brake per se being Well known to the art. Suflice it to say that washers 63 and 64 are secured to the upper and lower surfaces of the braking core, the arrangement being such that the rubber core 61 surrounds the piston rod 7, so that when air under pressure is introduced into the annular chamber 62 via line 14 the core 61 is deflected or compressed to exert frictional forces against the piston rod and to hold or terminate the movement of the carriage.

The housing is further formed with an upper air chamber 65 and a lower air chamber 66. It will be obvious to those of skill in the art that air is introduced into upper chamber 65 for the purpose of depressing the carriage and it is introduced into the lower chamber 66 to elevate the carriage. Means and methods by which these functions are performed are well 'known to those of skill in the art so that it is sufficient for purposes of the present invention simply to say, where appropriate, that such functions are performed.

As in the case of the Kohli invention referred to above, the brake system has three principal functions: 1) to hold the carriage 6 in an elevated position; (2) to release the carriage, permitting it to impact an anvil 13; and (3) to prevent multiple rebounding of the carriage 6.

The general operation of the invention is such that the carriage is first raised by the thrust of air pressure in chamber 66 on piston 8. In its fully raised position the carriage is held by the brake 61, full air pressure being applied through line 14. The carriage is held as air under pressure is introduced into the upper chamber 65 and the carriage is released and it falls and impacts the anvil 13, producing the shock wave, which is measured by means and methods well known to those of skill in the art. As the carriage rebounds it is arrested by the application of a lower and controlled air pressure to the brake via the regulator 69 and valve 70.

Referring now specifically to FIG. 1, there are shown the pneumatic lines and associated elements which function in such a manner that as the carriage is held in its position, preparatory to and during charging, full line air pressure is applied to the braking system, but so that, when the carriage is arrested on rebound after it has impacted the anvil 13, a controlled and regulated pneumatic pressure, less than full line pressure, is utilized for braking purposes, thus accomplishing the improvement in performance indicated by comparisons of FIGS. 2 and 3.

Specifically, there is a high pressure air source 67 in communication with pneumatic line 14 via solenoid valve 52, check valve 68, pneumatic line and solenoid valve 40, all in series. That portion of the high pressure line which comprises the check valve 68 and the solenoid valve 52 is paralleled by elements provided in accordance with the invention and comprising a regulator 69 and check valve 70. The regulator is provided with a suitable meter or gauge 71.

The operation of the FIG. 1 system is such that, when the carriage is in its fully raised position preparatory and during charge, full line air pressure is applied to the brake via the following elements: high pressure source 67, solenoid valve 52, check valve 68, line 10, solenoid valve 40 and line 14. On the other hand, when the rebound of the carriage is arrested, after the carriage impacts the anvil 13, a lower controlled and regulated pressure is applied to the brake via the following elements: source 67, regulator 69, valve 70, line 10, valve 40 and line 14. Under the last-mentioned conditions valve 52 is closed, thereby precluding the application of full line pressure to the brake.

The details of solenoid valve 40 are illustrated in FIG. 4, which shows the solenoid coil 11 in schematic form and a cross-sectional view of the valve per se. The valve per se comprises a housing 12 formed with a line 15 exhausting to atmosphere, the line 14 communicating with chamber 62, and the inlet pneumatic line 10. Reciprocally mounted within the housing is a double ended piston 16, which is so arranged that when coil 11 is energized the valve is in its closed position, against stops 79 as shown in FIG. 4, establishing communication from chamber 62 to the atmosphere via line 14, housing 12 of solenoid valve 40, and finally line 15. On the other hand, when the coil 11 is deenergized, the piston 16 moves to its open position, being compelled to do so by bias spring 72, establishing communication between the inlet line 10 and the outlet line 14 so that air pressure is applied to the brake, via elements 10, 40 and 14.

CYCLE OF OPERATION A typical cycle of operation of the invention is described in connection with the description of FIG. 5. FIG. 5 shows supply terminals 73 and 74, connected to a conventional 110 volt alternating current power supply.

Across the terminals and in series with a power switch is a solenoid valve 29, which is not a part of the invention and simply functions to open the high pressure source 67 and to make air available to the pneumatic system of the shock testing machine.

When switch 25 is closed, by encircuiting contacts 26 and 28, then terminals 75 and 76 are effectively the supply terminals and are hereinafter understood to be such.

Across the terminals 75 and 76 is a timer motor 34, in series with a switch 30, which is referred to as the cycle initiator switch. It is single-pole, double-throw switch comprising arm 31, an open contact 32 and contact 33. The switch is closed by encircuiting contacts 31 and 33, thereby starting the timer motor 34. The timer motor controls certain subsequent events in the cycle as will hereinafter appear. At this phase of operation switch is closed on contact 33 and switch 54 is closed on contact 57 and switch 44 is closed on contact 46.

In order to cause the carriage 6 to be raised, the timer motor 34 rotates arm 37 of switch 36 to the closed position at which contact 37 touches contact 38, energizing coil 11. Valve 40 closes and exhausts the air from the annular space 62, so that the carriage is freed. Arm 80 of switch 81 is also moved to the closed position, opening valve 35. Valve 35 remains open and it functions in such a way as to cause pressurized air to be admitted to chamber 66 from a suitable source (not shown), thereby raising the carriage 6. Valve 52 is closed by the application of power through switch 44 and remains closed at all times except when the carriage is in fully raised position. Parenthetical- 1y, valves 35 and 53 are similar in construction to valve 40, detailed in FIG. 4, in that they vent chambers 66 and 65, respectively, when closed.

The carriage continues to raise until it engages an upper limit switch 44, moving contact 45 into circuit with contact 47, so that coil 48 of the relay 43 is energized, via contacts 49 and 50. Relay arm 42 is thus switched from contact 41 to contact 51, with the following results: solenoid valve 35 closes so that piston 8 is no longer thrust upwardly and chamber 66 is vented; solenoid valve 53 is opened, causing high pressure air to be admitted to upper chamber 65, and power is removed from solenoid valve 40, opening it. Additionally, as contacts 45 and 47 touch, valve 52 is deenergized and opens, so that full line air pressure is applied to brake 61.

Referring now specifically to relay 43, it comprises a coil 48 in circuit, across the supply terminals, with the upper limit switch 44. The coil 48 becomes energized in response to the closing of this circuit to switch its moving contact 42 from contact 41 to contact 51.

Under the assumed conditions contact 51 is hot, valve 53 is open, valve 52 is open, and valve 40 is open. Valves 40 and 52 being open, full line pressure is applied to the brake via the elements 52, 68, 10, 40 and 14, so that the carriage is held in elevated position. Valve 53 being open, charging air is admitted to the upper chamber at whatever pressure is desired by the operator.

The next phase of the cycle is the shock test phase, at the initiation of which the carriage 6 descends. The timer motor rotates switches 36 and to the second position, contacts 37 and 38 touching, so that valve 40 is closed, exhausting the brake air and permitting the carriage to descend. Valve 35 is also closed, as switch 80 is opened.

The carriage descends at a rate determined by gravity and by the charge air pressure until it impacts against the machine anvil 13. As the carriage withdraws downwardly from switch 44, the switch 44 is operated, contacts 45 and 46 closing, so that valve 52 is closed, the 6611 of relay 43 is deenergized and contact 42 of the relay 43 then moves into the position of engagement with contact 41.

Near the bottom of the descent, at a predetermined point above the anvil 13 which is determined by the operator, the carriage engages the rebound control switch 54, rotating arm 55 to the open position in contact 'with contact 56, so that power is removed from valve 40 whereby valve 40 opens and admits the regulated air pressure into the annular space 62.

Air is supplied to the annular space 62 through the regulator 69 and check valve 70 and valve 40. The regulator 69 permits the air pressure introduced to the annular space via valve 40 to be the minimum pressure required to prevent secondary impact after rebound.

The air pressure within the brake space 62 rises to the pressure previously selected by the operator and gradually deflects the elastic core 61 against the piston rod 7 as the carriage rebounds from the machine anvil 13. The carriage is thus gradually brought to rest with a minimum braking force and a corresponding minimum carriage deceleration. The switch 55 is positioned, and the regulated air pressure is selected, so that the carriage braking will begin just after rebound in a manner that will prevent secondary impact against the anvil 13.

The upper limit switch 44 corresponds generally to the switch 103 of the above-mentioned Jensen et al. Pat. 2,955,456 and the rebound switch 54 corresponds generally to the rebound switch S shown in the Kohli Pat. 3,103,116 referred to above.

While there has been shown and described what is at present considered to be the preferred embodiment of the invention, it will be understood by those skilled in the art that various modifications and changes may be made therein without departing from the true scope ,of the invention as defined in the appended claims.

Having described our invention, we claim:

1. In a shock testing machine of the type comprising a reciprocally movable carriage, an anvil adapted to be impacted by the carriage, said carriage being mounted to be raised, depressed and arrested after rebound'with said anvil, and a braking system responsive to the application of air pressure to hold the carriage in a raised position or to arrest the carriage after rebound, a braking system control comprising:

a first means for applying air to the braking system at a first relatively high predetermined level of pneumatic pressure for holding the carriage in raised position;

a second means for applying air to the braking system at a second and lower predetermined level of pneumatic pressure to arrest the carriage after rebound; and

means responsive to displacement of said carriage to raised position for selectively actuating said first means and responsive to approach of said carriage to rebound for selectively actuating said second means.

2. Apparatus as in claim 1 wherein:

said shock testing machine further comprises means for forcibly urging said carriage from said raised position towards said rebound position;

said braking system is responsive to said first air applying means for applying a sufficient braking force on the carriage in the raised position to resist said forcible urging means and prevent movement of said carriage; and 1 said braking system is responsive to said second air applying means for applying a sufiicient braking force to said carriage after rebound of said carriage to gradually terminate its movement and prevent a second rebound thereby minimizing secondary shock pulses applied to said carriage by said braking system.

3. Apparatus as in claim 2 wherein said firstjand second means for applying air to said braking system comuse:

p a source of air at said relatively high predetermined level of said pneumatic pressure;

a first flow path extending from said source of air to said braking system;

a means for providing a second flow path from said source of air to said braking system; valve means interposed in said second flow path for providing in said second path a lower predetermined level of pneumatic pressure to said braking system; and valve means interposed in said first flow path means for selectively permitting relatively unrestricted flow of air from said source'to said braking system and for terminating flow through said first flow path means, said valve means in said first flow path being re sponsive to displacement of said carriage to said raised position for permitting flow to said braking system through the first path and responsive to approach of said carriage to said rebound position for terminating flow through said first flow path thereby causing flow of air through said second flow path. 4. Apparatus as in claim 3 wherein: the valve means in said second flow path means comprises a pressure regulating valve and a downstream check valve only permitting flow to said braking system; the valve means in said first flow path comprises a twoposition valve for selectively permitting flow through said second flow path and a check valve downstream of said two-position valve and only permitting flow to said braking system. 5v Apparatus as in claim 4 wherein said pressure regulating valve is adjustable to vary the lower predetermined level of pneumatic pressure applied to said braking system.

6'. In a shock testing machine of the type comprising a vertically reciprocally movable carriage, an air-operated piston assembly for'raising and depressing said carriage, an anvil adapted to be impacted by the carriage, and braking means releasable to permit the carriage to fall and responsive to the application of air pressure to hold the carriage in elevated position or to arrest the carriage after rebound, as desired, the improvement comprising:

cycling means having a first state for issuing a first electrical order for the carriage to be raised and having a second state for issuing a second electrical order for the carriage to fall and to be held on rebound,

a selector having first and second states indicative that the carriage is not or is, respectively, in raised position,

a first source of high pressure air,

a first solenoid valve means in a flow path with said braking means for controlling admission of air to said braking means,

means for electrically encircuiting the first solenoid valve means with the cycling means and the selector so that the first solenoid valve means is disabled and the carriage is not braked when the selector and cycling means are in their first states,

a second solenoid valve means for controlling air to said piston assembly for raising said carriage,

means for electrically encircuiting the second solenoid valve means with the selector so that'the second solenoid valve means is enabled when the cycling means is in its first state,

a third solenoid valve means in a flow path with said first valve means and said source,

means for normally disabling the third valve means but electrically enabling the third valve means when the carriage is in raised position and also for activating the selector into its second state, so that both the first and third valve means are open to apply high pressure air to said brake and to hold the carriage in elevate position,

means including a fourth solenoid valve means and responsive to the second state of the selector for charging said piston assembly with compressed air,

thereby causing the piston assembly to urge said carriage in a direction towards said anvil,

said cycling means issuing the second order after charging whereby the carriage falls and the first, second and third valve means are disabled,

a second source of air at a pressure lower than that of the first source,

said first valve means being also in a flow path with said second source, and

means responsive to the approach of the carriage to 10 rebound for enabling said first valve means whereby air at said lower pressure is applied to the brake to terminate rebound.

References Cited UNITED STATES PATENTS 2,955,456 10/1960 Jensen et a1. 73-12 2,967,590 1/1961 Ottestad 73l2UX 3,064,464 11/1962 Black et al. 73l2 3,103,111 9/1963 Kohli 7312 CHARLES A. RUEHL, Primary Examiner

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