Abstract:
A tester responsive to repetitive impact blows. A brake is interposed between an impact target and a base to exert a frictional braking force on the target so the effectiveness of repetitive blows on the target can be assessed.

Description:
FIELD OF THE INVENTION 
     A tester to test the ability of a subject to apply sufficient percussive blows to achieve a defined result within a specified time. 
     BACKGROUND OF THE INVENTION 
     In fields which require its personnel to have strength and stamina sufficient to perform certain vigorous tasks, it is not suitable to wait until the moment arrives to learn whether the person has the ability or not. Instead, tests must be devised for use during the hiring and selection process to eliminate the unqualified, as well as to be certain that the ability is retained by those who are hired. 
     Such tests, especially when hiring for publicly paid and competitive openings, and for retention and promotion, must be subject to standardization. This is required not only for fairness and adequacy of the test, but often by contract requirements which specify these requirements. Certainly they should be repeatable from test to test and from person to person. 
     An example of such a requirement is the ability of a fireman to knock a hole in a wall. The fireman must use a sledge or an axe, and in action he or she must strongly swing it with sufficient force and momentum as to break through the structure. In action, a single blow rarely accomplishes this, although it might. Instead, repeated blows are nearly always required. 
     Importantly, every one of the blows must be strong enough to damage the structure. Merely bouncing an axe off of a wall would be an exercise in futility. Thus, the person must have the strength to deliver sufficiently strong blows and the endurance to pound them repeatedly on the structure, each time with a damaging effect and finally with a cumulative effect. While a stronger blow is obviously better than a weaker blow, the force of each blow is not the answer. It is the accumulation of blows of damaging energy, and importantly how long it takes to get into the structure, which is in turn a function of how many blows by that person are needed. A too-long succession of lesser blows will not serve in fighting a fire. Thus, the test must measure the ability to achieve a given test result, and the time it takes to do it. 
     It is an object of this invention to provide a test device which can measure the person&#39;s capacity to create a given result with successive blows, and how long it takes for it. 
     Also, the test must be consistent from test to test and from person to person. 
     It is another object of this invention to provide a tester which can be calibrated before each test is started. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A tester according to this invention includes a base to which a target is slidably mounted. A brake is interposed between the target and the base to resist movement of the target when it is percussively stuck. The brake is adjustable to enable its resistance to be calibrated. 
     A calibrator that includes a removable yoke and piston/cylinder assembly are temporarily mounted to the base so as to exert a selected static force on the target. The brake is adjusted to allow the target just to move when the calibration force is exerted, thereby to standardize the test from user to user. 
    
    
     The above and other features of this invention will be fully understood from the following detailed description and the accompanying drawing, in which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front elevation of the preferred embodiment of the invention. 
     FIG. 2 is a right had side view of FIG. 1 taken at line  2 — 2  therein; 
     FIG. 3 is a view principally in cross-section taken at line  3 — 3  in FIG.  1  and 
     FIG. 4 is a more detailed cross-section of a portion of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The tester  20  includes a base  21   a  which in use will be mounted to a vertically-supporting structure (not shown) such as a wall or a very rigid and stable stand. A target  21  is mounted to four guides  22 , which are aligned with a central axis  23 . The target has an impact surface  24  that is normal to the axis. Circular strike pad  25  at the center of the exposed surface  26  of the target is where the tested person is expected to direct his blows. 
     The structure is generally rectangular. The base has four guide passages  30  that slidingly receive the guides  22 . They are parallel to the axis. The objective is for the tested person to drive the target axially so the guides  22  will slide in the guide passages as the target is driven along the axis. 
     The axial movement of the target is resisted by a brake  35 . The target itself is comprised of an impact resistant material, such as a stack of individual sheets  36  of fabric-reinforced tire material held in a tight pack by a basket-like enclosure  37 . The stack is tightly compressed and is conveniently formed of layers of the material, whose upper edge is exposed to the blows. The impact surface  24  is the upper face of this stack. The bottom  38  of the basket, and the rest of the basket itself are made of strong metal so as not to be substantially deformed by the blows which are to be received. 
     The object of the invention is to provide means to resist the movement of the target toward the base in such a way as to reflect the capacity (ability) of the tested person to exert sufficient blows in a sufficiently limited period of time to do the work required for this movement. If he has that capacity, it will follow that he inherently has the capability to deliver blows under active conditions that would be sufficient for the purpose. In addition, as a competitive matter, the test must be consistent from person to person and to provide relative ratings. 
     For this purpose, a brake blade  50  is fixed, perhaps by a weldment, to the bottom of enclosure  37 . It passes through a slot  51  in the base. The blade has a pair of opposite braking surfaces  52 ,  53 . These are smooth, and are abutted by a pair of brake pads  54 ,  55  which bear against surfaces  52  and  53 , respectively (see FIG.  4 ). The objective is to resist the axial movement of the target as it is driven by blows exerted on the target. This is a typical friction braking arrangement, in which the resistance is a function of applied braking pressure and the coefficient of friction. 
     In order to exert restraining pressure by the brake pad on the brake blades, four sets of two opposing spring bias elements  60 ,  61 ,  62 ,  63  are provided. These are all identical, so only element  60  and will be described in detail. 
     As best shown in FIG. 4, brake blade  50  passes through a gap  65  between brake pads  54  and  55 . These pads are held in recesses  68 ,  69  in mounts  70 ,  71  respectively. The blade has an axially extending central slot  72  for a reason to be disclosed. In use, the mounts bear downwardly on the base. 
     The pads are backed by steel plates  73 ,  74 . The mounts have holes  75  therethrough to pass bolts  76 , these bolts being threaded on both ends. Compression springs  80 ,  81  surround these bolts, one on each side of the mount. 
     An adjustment nut  82 ,  83  is threaded to each end. Tightening the two nuts will compress the spring and adjustably set the pressure of the brake pads on the blade. In FIG. 4 the assembly is set in a blade-release mode, as will be seen. Thus, when the pads bear against the blade, their applied force can be adjusted by turning the nuts. 
     After the blade has been driven into the brake during a test, it will be tightly gripped by the brake and will be difficult to raise for the nest test. To attend to this situation, a brake release  90  is provided. A nut  91  is fixed to mount  71 , and a release bolt  92  is threaded into it. It freely passes through the pads, steel plate  74 , and the slot  72  in the blade, and can bear against steel plate  73 . It has a suitably large hand wheel  93  to turn it. Turning the wheel will press against plate  73  and thereby push mount  70  away from mount  71  so as to release the brake. The target can then easily be raised for the next test, after which the wheel is turned the other way so as to release plate  73  from abutting contact, and the brake will then again be pressed against the blade by the springs. Stops  94  on the ends of the guides prevents the target from being lifted off the base until they are removed. 
     Adjusting the spring&#39;s compression will determine the braking force applied to the blade to resist axial movement of the blade and of the target. 
     It is desirable, but not necessary, for there to be a small angle, perhaps no more than about 5 degrees between the faces of the brake blade which preferably will be planar. This prevents a too-free passage of the blade along the brake pads. As a consequence, the driving force needed may be somewhat greater as the target is driven further. 
     It will be appreciated that unless there is a sufficient braking force, the target would supply slip downwardly and nothing could be learned. The object is to set the braking force at such a level that a suitable test subject would be able to drive the target to its destination in a given time. 
     There is no definitive way to adjust this device. Instead it must be calibrated to reflect the needs felt by senior and experienced men, such as fire captains who have had years of experience and know “in their bones” what it takes. This device can be set (calibrated) to recognize their opinion as to sufficiency. Then all similar devices can be set the same. 
     For this purpose, a calibrator  100  with removable yoke  101  can be hooked to attachments  102 ,  103  on the base, with a bight  104  that overhangs the target when in place. A hydraulic (or pneumatic) cylinder  105  is fixed to the bight. A piston rod  106  attached to a piston (not shown) extends from the cylinder and bears against a foot  107  which in turns bears against the target. 
     A source  110  of fluid pressure such as a gas bottle or a pump provides fluid through a pressure regulator  111  and gauge  112  to the cylinder. Next the brake is tightened with the target raised. A selected pressure is applied, leading to an applied force on the target from the foot. At some pressure and setting of the brake, the target will begin slowly to move. The calibration will, of course, be removed when the target is to be struck. 
     Now the person calibrating the device has a place to start. With the brake setting and the known pressure, he removes the yoke and beats on the target with a selected implement. If it is too easy, he will know. Also he will know if it is too difficult. There will follow a few more adjustments of tightening or loosening the bias and of changing the pressure. Best procedure will be to select some fluid pressure, perhaps 700 psi, and adjust the brake pad bias. 
     Soon the device will feel right to an experienced man who is pounding on the target. The fluid pressure setting can be agreed on. Then from device to device, and from test to test, the brake bias will be set so as just to start moving at that pressure when the foot is in place. Now there exists a readily repeatable and reliable tester that reflects the needs of a suitable person such as a fire fighter. Notice that with an agreed pressure, there is only the need to adjust the spring forces on the brake. 
     Because completion of the test involves applying sufficient blows of sufficient strength within a specified time period, a limit switch  115  or other type of sensor is mounted where it will be contacted by a target driven through a sufficient distance. A timer  116  can be coupled to the limit switch to indicate how long it took for the switch to be closed. There results a tester useful to determine whether a person can, within a stated time, achiever a desired result with repeated precussive blows. 
     While measuring the ability to knock a hole in a wall is the presently-known best use for this device, it is also useful for testing the capacity to perform other functions which include percussive blows. 
     This invention is not to be limited by the embodiment shown in the drawings and described in the description, which is given by way of example and not of limitation, but only in accordance with the scope of the appended claims.