Application of Oelrich

• Decision Date: 15 June 1978
• Docket Number: Appeal No. 78-502.
• Parties: Application of John A. OELRICH and Albert J. Divigard.
• Court: U.S. Court of Customs and Patent Appeals (CCPA)

579 F.2d 86

Application of John A. OELRICH and Albert J. Divigard.

Appeal No. 78-502.

United States Court of Customs and Patent Appeals.

June 15, 1978.

Roger A. Van Kirk, Fishman & Van Kirk, East Hartford, Conn., atty. of record, for appellants.

Joseph F. Nakamura, Washington, D. C., for the Commissioner of Patents, Thomas E. Lynch, Washington, D. C., of counsel.

Before MARKEY, Chief Judge, and RICH, BALDWIN, LANE and MILLER, Judges.

RICH, Judge.

This appeal is from the decision of the Patent and Trademark Office (PTO) Board of Appeals (board) affirming the rejection of claims 1-5 in appellants' application serial No. 452,050, filed March 18, 1974, for "Sub-Critical Time Modulated Control Mechanism," under 35 USC 103 as obvious from U. S. Patent No. 3,430,536 for "Time Modulated Pneumatically Actuated Control Mechanism," issued March 4, 1969, to John A. Oelrich, one of the present joint applicants. We reverse.

The invention relates generally to control mechanisms used, inter alia, to move steering fins on guided missiles. The device responds to an electrical signal from the missile guidance system, variously described as the "command," "input," or "error" signal, the magnitude of which is proportional to the desired amount of course-correcting fin movement, and converts this signal into a pneumatic pressure of appropriate magnitude which acts on a piston to move the fin. Before describing the particulars of the claimed invention, we will briefly describe the prior art control devices cited by the PTO which appellants concede to have been the starting point of their invention.

An exemplary embodiment of the prior-art actuator described in the Oelrich patent is illustrated below:

Cyclic energization of solenoid 6 by a periodic carrier signal (illustrated) alternately pressurizes and exhausts piston working area 18. The cycle is so fast that time delays resulting from the size of inlet port 10(Au) and exhaust port 11(Ad) cause a steady-state pressure to be approximated in area 18 which is balanced by constant pressure on piston surface 20 when the control is in the neutral or "null" position. When a command signal (illustrated) is superimposed on the carrier signal in summing amplifier 14, switch 29 responds to the altered signal to alter the relative durations of solenoid energization and solenoid de-energization within each cycle.

For example, a command signal increasing the magnitude of the signal which reaches switch 29 will cause the solenoid to be energized for a greater portion of each cycle than it is de-energized. Accordingly, pressurization time is greater than exhaust time, the approximate steady-state pressure in area 18 is increased, and piston 28 moves to the right, thereby moving the steering fin (not shown). If the command signal decreases the magnitude of the signal reaching switch 29, the solenoid will be de-energized for a greater portion of each cycle than it is energized, exhaust time will be greater than pressurization time, the steady-state pressure in area 18 is reduced, and piston 28 moves to the left. Such operation of the actuator is said to be "time modulated."

At any given time, the pressure in area 18 will fluctuate somewhat in accordance with the frequency of the bursts of pressurized gas received therein, which, in turn, depends on the carrier signal frequency. These pressure variations cause slight load (fin) movements attributable to the carrier signal rather than the command signal, and such movement is termed "dither." Some dither is desirable in overcoming friction, often termed "coulomb friction," which might otherwise cause the control to stick in its neutral position. Such a desirable degree of dither is manifested as a slight vibration of the device. Excessive dither, sufficient to cause significant load (fin) movement, is obviously undesirable. The pressure fluctuations that cause dither are known to depend, inter alia, on the impedance or responsiveness of the load and the carrier signal frequency.

A second factor governing operation of the Oelrich control systems is that each such system has a natural resonant frequency, sometimes termed "critical frequency." When excited by a carrier signal at the critical frequency, system response is out of proportion to input; that is to say, uncontrolled oscillation of the steering fin occurs.

The parties seem to agree that the device disclosed in the Oelrich patent was employed only with the then available steering fins which they characterize as "high inertia" loads. According to Fig. 7 of the Oelrich patent, dither amplitude, expressed in terms of "dither amplitude ratio,"¹ and carrier frequency in systems employing such loads were known to be related generally as follows (increasing spring rate connotes increasing load, and resonant peaks (broken lines) are shown as moving to the right with increases):

The Oelrich patent states that it is preferred to operate the control using carrier frequencies above the critical frequency in order to obtain the desired low dither amplitudes in the area where the curves converge. The control there described, however, is subsequently characterized as "adapted to receive a carrier frequency substantially in excess of the particular system critical or resonant frequency * * *."

The Invention

With the advent of light-weight missile steering fins, it became desirable to employ the Oelrich control with low inertia loads. It was found, however, that the critical frequency of such a system was so high that super-critical operation exceeded the practical capabilities of available solenoids, which are stated to have an upper frequency limit of about 175 Hz. Appellants discovered that the Oelrich control, coupled to a low inertia load, can be operated with a sub-critical carrier frequency without incurring unacceptably large dither which, they allege, would have been expected by those of ordinary skill in the art based on the known frequency-response characteristics of high inertia systems. Claims 1 and 2 are illustrative and read (emphasis ours):

1. A time modulated fluid actuated control apparatus comprising:

housing means, said housing means defining a cylinder; actuator piston means disposed in said housing means cylinder; said piston means including an output member adapted to be connected to a movable load, said load and control apparatus defining a system having a range of resonant frequencies;

solenoid operated valve means mounted on said housing means, said valve means being selectively operable to deliver pressurized fluid to and to vent fluid from said housing means cylinder at one side of said piston means;

means for generating variable input command signals commensurate with the desired position of the load, said command signals being characterized by a dynamic frequency range below said range of said resonant frequencies;

means for generating a signal at a carrier frequency, said carrier frequency being greater than the maximum dynamic command signal frequency and less than the minimum system resonant frequency;

means for modulating said carrier frequency signal by said command signals; and

means responsive to said modulated carrier frequency signal for controlling energization of said solenoid operated valve means.

2. The method for the control of a pneumatic position control mechanism employing an expansible chamber motor having an output shaft couple sic to a movable load, said method comprising the steps of

generating a command signal commensurate with the desired position of the movable load coupled to the control mechanism motor output shaft, the frequency of the command signals being within a range determined by the primary band width of the actuator system including the control mechanism and the load;

generating a carrier signal at a frequency less than the minimum resonant frequency of the actuator system and greater than the maximum command signal frequency;

modulating the carrier frequency signal with a command signal; and

controlling the delivery of pressurized gas to the position control mechanism expansible chamber motor in accordance with the magnitude of the modulated carrier frequency signal.

The Rejection

The examiner rejected claims 1-5 under 35 U.S.C. § 103 as obvious from the Oelrich patent, noting the reference's specific teachings that carrier frequencies yielding "a degree of dither" were desirable and that super-critical operation was merely preferred.² The general teachings of Oelrich that carrier frequency should be selected to optimize system performance indicated to the examiner that selection of a particular carrier frequency was "a mere choice in design" and that optimization of a low-inertia system...