US1768718A - Percussive device - Google Patents

Description

y 1930- c. R. SODERBERG 1,768,718

PERCUSSIVE DEVICE Filed July 2'7, 1927 2 Sheets-Sheet l F/Lg, Z

INVENTOR (ZYI/ 1?. Sow/leg? A'TTORNEY July 1, 1930. c. SODQERBERG Psncuss'Ivs DEVICE Filed July 27, 192T 2 Sheets-Shget 2 6 5,0 ec/f/c fipee h fis u mgxow INVENTOR [57/ A? Sade/day ATTORNEY Patented July 1, 1930 UNITED STATES PATENT OFFICE CARL RICHARD SODERBERG, OF EDGEWOOD, PENNSYLVANIA, ASSIGNOR TO WEST- INGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA PERCUSSIVE DEVICE Application filed July 27,

My invention relates to percussive devices and particularly to such devices wherein a peripdic force is utilized to actuate a hammer hea One object of my invention is to provide a percussive device wherein the several parts and the forces utilized for actuating the parts are so related to each other as to secure stable operation of the deviceand produce impacts of maximum intensity in an efficient manner.

Another object of my invention is to make devices of the above-described character wherein the frequency of the blows of the percussive device will be a fraction of the frequency of the periodic force acting upon the hammer head.

A further object of my invention is to provide percussive devices that will operate in a stable manner, notwithstanding slight variations of the conditions of operation and the constants determining the operating characteristics.

I have found that a very efiicient and simple percussive tool for chipping, riveting, etc., may be constructed by combining a hammer head adapted for reciprocal motion with a suitable energy-storing means, such as a spring, for biasing the same towards an anvil or tool holder, and electro-magnetic means for periodically lifting the hammer;v head from the anvil, provided that the several elements constituting the mechanical oscillating system so obtained have certain definite relations to each other and to the periodic,

externally-impressed force acting thereon.

The foregoing and other objects of my invention will be best understood by reference to the accompanying drawings, wherein Figure 1 is a view, partially in section and partially in elevation, illustrating a hammer of the single-solenoid type to which my invention is applied,

Fig. 2 is a view, similar to Fig. 1, illustrating a hammer of the double-solenoid type,

embodying my invention, a v

Fig. 3 is a circuit diagram'illustrating the conne tions of the solenoid coils employed in the evice shown in Fi 2,

Fig.- lis a diagrammatic view of the elements constituting the mechanical oscillat- 1927. Serial No. 208,811.

ing system of the devices shown in Figs. 1

mer head 1, of magnetic material, is mounted a for reciprocal movement within a non-magnetic cylindrical guide member 2 that is held within a hollow cylindrical casing 3 of magnetic material. The hammer casing 3 is provided, at its top portion, with a suitable handle 4 which may be gripped by the operator. At its lower end, opposite the handle, the easing is provided with a constricted cylindrical chamber 6 having movably disposed therein a tool holder or anvil 7 that has an impact surface 17 which projects toward a similar surface 18 on the hammer head 1. In order that the anvil 7 may not bear rigidly against the end of the casing 3, a spring 5 is interposed therebetween within the cham- The anvil 7 carries a suitable impact tool,

such as a chisel 8, that projects through an opening 9 in the bottom of the hammer casing 3 toward the work piece 10 to which it is to be applied.

The hammer head is held, under pressure, against the anvil 7 by means of a compression spring 11 which reacts against a spring rest 12 that is held by the upper end wall of the casing 3. 'The spring rest 12 is adjustable in an axial direction by means of an adjusting screw 13 to permit variation of the compressive forces that may be applied to the spring 11 to change the force which biases the hammer head 1 against the impact surface 17 of the anvil 7 when the hammer is at rest.

The hammer is supplied with power by means of a solenoid 14 that is disposed around the non-magnetic guiding member 2 for the magnetizable hammer headl. It may readily be seen that the hammer head 1 operates as an armature or plunger for the solenoid 14. When the solenoid is energized, the plunger or hammer head 1 is withdrawn from the anvil 7, thereby compressing the spring 11 and storing potential energy therein which is subsequently transmitted to the hammer head 1 as kinetic energy and released in an impact upon the anvil 7 Energization of the solenoid 14 is usually effected by means of an alternating current, although the hammer may be operated by means of any periodi-' cally interrupted electric current. In the embodiment of the invention illustrated, conductors 15 are provided for connecting the solenoid 14 to a suitable power source.

When the hammer shown in Fig. 1 is energized from a source of alternating electric current, such as a GO-cycle current, the magnetic flux induced by the solenoid 14 exerts a periodic force upon the plunger or hammer head 1 tending to pull it toward the center of the solenoiod twice during every cycle of the current. Thus, it is evident that the solenoid 14 exerts 120 force impulses per second, upon the hammer head 1 in a direction away from the anvil 7 and against the action of the spring 11. The magnetic and spring forces so acting upon the plunger may be considered as being equivalent to an alternating force pulling the hammer head away from the anvil and subsequently projecting it toward the same.

In analyzing the operation of the hammer device, it is desirable to deal with an alternating force rather than with a pulsatory force acting upon the movable hammer head. Accordingly, I shall hereinafter consider the initial spring pressure as a resultant of the actual initial sprin compression and the average value of t e unidirectional component of the pulsating force acting upon the hammer head. The force acting upon the hammer head or plunger may then be considered as being an alternating force, and, in the idealized conditions, the alternating force may be assumed to be a pure harmonic force. Such assumption will not, in any way, disturb the results and the conclusions derived from the analysis, since, for practical purposes, it is sutficient to consider only the major harmonic component of the force acting upon the hammer head and to neglect the in uence of the minor harmonic components.

In the hammer device shown in Fig. 2, the essential elements of the mechanical hammer system are the same as those in Fig. 1, except that the magnetic force exerted upon the hammer head 1 is of an alternating character instead of a. unidirectional pulsatory character. The alternating force is obtained by means of two solenoids 21 and 22 placed at different positions with respect to the length of the hammer casing and alternately energized, by means of two rectifiers 24 and 25 (Fig. 3) from an alternating-current source 26. liy utilizing the construction shown in Figs. 2 and 3, the frequency of the force acting upon the hammer head 1 is made equal to the frequency of the alternatingcurrent.

Referring now to Fig. 4 the mechanical oscillating system, which is diagrammatically represented therein, comprises a hammer head 1 that is assumed to embody the entire mass of the system and a substantially weightless spring 11 that constitutes the resilient member. The hammer head 1 is assumed to be mounted for reciprocal motion without friction along a hammer axis X-X that is inclined at an angle b to the horizontal. The angle 6 represents the inclination of the hammer with the earths surface when it is in actual use.

At the upper end of the hammer axis X-X, a spring rest 12, that is assumed to be perfectly rigid, is provided for resisting the reaction of the spring 11.

The motion of the hammer head 1 is limited, in the downward direction, by an anvil 7 that is also assumed to be perfectly rigid but is supposed to be able to absorb a certain amount of energy from each impact of the hammer head 1.

It will readily be seen that this mechanical system constitutes an oscillating or vibrating system of one degree of freedom that has a definite natural period of vibration which depends upon the mass of the hammer head 1, the resilience of the spring 11 and the. manner in which they are mounted.

It will be further assumed that the resultant of the forces imparted to the hammer head 1 by the solenoid 14 or the solenoids 21 and 22 shown in Figs. 1 and 2 or b other means is a simple harmonic vibratory orce that may be represented by the project-ion on the hammer axis of a force vector F that rotates at a uniform angular velocit in a plane containing the hammer axis The hammer may be adjusted to deliver blows at a frequency which is a certain fraction of the frequency of the applied force.

For example, if the hammer shown in Fig. 1 is utilized with standard 60 cycle current, the solenoid 14 will exert 120 force impulses per second upon the hammer head, as explained hereinbefore. Under these circumstances, it is possible to make the hammer head strike against the anvil 120, 60, 40, etc., times per second, corresponding to 1, 2, 3, etc., force cycles per blow. The mode of operation then may be said to be 1, 2, 3, etc.

The natural frequency of oscillation of the hammer head, when its motion is not obstructed by the anvil, and the initial compression of the spring determine the mode of operation.

The energy that is imparted totlie hammer head 1 by the impressed magnetic force is head, suflicient energy is stored in the spring 11 to insure that the re uired impinging velocity will be developed uring the downward stroke.

The particular condition under which a hammer embodying the invention will operate most effectively andthe method of proportioning the various parts thereof to obtain the exact relationship between the natural frequency of oscillation of the hammer head, the initial compression of'the spring and the mode of operation, will be more fully set forth in the following mathematical consideration. In expressing the 'mathematical relations leading up to the principle of operation of my device I shall 'use the following notations Weight of the hammer head W Mass of the hammer head M Scale of the spring or the resisting force per unit deformation lc Angular velocity of rotation of the force vector u Angular velocity corresponding to the natural frequency of the hammer head when its motion is not obstructed by the anvil u Amplitude of forced oscillations of the hammer head when its motion is not obstructed Initial compression of the spring m Compression of the spring corresponding to the component of gravity and the constant part of the pulsating force w Equivalent initial compression of the spring w Spring function ..8 Speed function R Referring to Fig. 4, the alternating force acting upon the hammer head 1 may be represented by a force vector F that rotates at a uniform angular velocity u and exerts a harmonic component in the direction of the hammer axis XX. This harmonic component may be expressed as a sine function of the force F having a periodicity of u.

The condition of equilibrium, for the forces acting upon the hammer head at the time t after the force vector points in the negative w-direction, when the head has moved a distancew, from the anvil, is given by the equation The efl'ect of the weight of the hammer head 1 may be expressed by the corresponding displlacement or compression m 0 the spring, t us v W elicm b (2) Thus if ca is introduced as representing an equivalent spring compression, where The equation of motion may be written 2 M%+k(z +x)= F cos at (4) Als ointed out hereinbefore, where the app 1e stead of an oscillatory character, the unidirectional component of such force may also be represented by a corresponding spring compression, and it may be embodied in the equivalent initial spring compression w of equation (3).

The solution of equation (4) is The quantity u represents the angular velocity corresponding to the natural frequency of oscillation of the hammer head 1, when its motion is not obstructed by the anvil 7 and has the value The specific speed 9 is defined as the ratio of the actual angular velocity of the force vector to u thus also ' i" L a q flcMu Mu 9 -1 (7) The quantity (1 represents the amplitude of oscillation of the hammer head 1 under influence of the force F when its motion is not obstructed by the anvil 7. With the introduction of and a the solution may be written in the 0 lowing form r Thus w=o ut==G (9) z+z =A cos -l-B em -5+0 cos at (8) force is of a pulsating character iii-- The hammer head is leaving the anvil with a certain velocity 'v that is,

w=o ut=21rn+6 (11) By introducing the conditions (9), (l0) and (11) into equation (8) and its derivations we obtain the following equations x =A cos gi-B sin gi-a cos (12) g%= A sin g+B cos g-wtg sin G (13) x =A cos +acosG (14) These equations give the following values for the integration constants A and B.

=2 q B g+ag sm 9 and, for the determination of the angle G ze -a, cos G=(Zlq+aq sin G) cot (17) The displacement and the velocity of the hammer head are now The velocity with which the head strikes the anvil is now obtained from equation (19) by putting ut== 21rn+ G. This velocity will be denoted by o being directed in.the negative direction of m. We obtain o o =2 au sin G (20) The first requirement for sustained and efficient operation is that the increase in the velocity of the hammer head between blows, o 'v shall be positive. Now, the quantity a, equation (7), is positive if q is greater than 1, that is, if the hammer operates above the natural frequency of the hammer head, but it is negative if Q is less than 1, that is, when the hammer operates below the natural frequency of the hammer head. Consequently, the angle G must not vary beyond the following limits At each impact of the hammer head upon the anvil, a certain amount of energy is dissipated in the form of work done by the tool. The impact reduces the impinging velocity c of the hammer, and, if this dissipation is complete, there will be no rebound, that is, 22 will be equal to zero. Usually, all the energy latent in the blow is not dissipated, so that the return velocity 42 will have a small value which is expressed The constant 6 being a coefficient of restitution dependent upon the efiiciency with which the tool is working. It is evident that e depends not only upon the tool itself, but also upon the support of the working piece and other factors. lVith the introduction of the coefficient of restitution, I can express o, and Q2 separately and find that au sin G (24) au sin G Consequently the energy E dissipated in one blow may be expressed as if 2 0, 11, sin G (26) 1rn+G-u (x+a: (x a cos G) q +a cos at (18) cos sin vrn-l-G-ut g= (v au sin G) i au sin at (19) that is,

The determination of the impact angle G from equation (17) gives Z'R sin G-i-cos a=s 27 when 1 e n A 5' sm G fig whereupon equation (27) becomes sin (G+G )=sin G a (31) This equation in G has two roots G za-ca and G=1rG G 32 A sustamed sequence o OPeIatmg cycles 15 i t possible only if the quantities S andR are so ad'usted that these two roots are identical.

This is possible only if |S'= ;t 1+R (33) and then the angle G assumes the value Gr denotes the special positive or negative value that G assumes when R is positive,

G =cot- R 34 Equation (33) expresses the second reuirement for sustained operation, and I s all now'deduce from thisrrequirement, and the one previously found, in equations (21) and (22) the physical design proportions of the hammer, to which they correspond.

The values of the angle G, which are obtained from equation (32) depend upon the sign of the spring function S and of the speed function R. I

The quantity S derives its sign from both w and a. Theoretically, both of these may be either positive or negative,'but, since there are certain practical difiiculties in arranging springs of this kind for alternating tension and compression, I disregard the possibility of negative values of m so that the sign of S will be the same as that of a. Consequentl o n e and negative when 9 is less than one.

The quantity B may be assumed tempora- The quantity S is de- S will be positive when 9 is greater than rily to have both positive and negative values, depending upon the value of 001:

Four possible combinations are thus obtamed, to each of which correspond a certain value of the angle G. These combinations are (a) R 0 and S O, g 1

a= "-G. (35) (b) R 0 and S 0, 9 1

1r (5%) (0) R o and a o, g 1

0= g-0..) (37) (d) R 0 and S 0, g 1

Now referring to the conditions alread established in e nations (21) and (22), find that cases (a and (0!) do not represent possible operating conditions, because they conflict with this requirement. For this reason, operation of the hammer is restricted to positive values of the speed function R, that If must always remain positive, so that there i are two ranges of val ass for the argument of the specific speed q c etc.

Sustained operation is always possible for values of the specific speed above 2n. No

operation can take place between n and 217 but below 1 there is a series of narrow strips within which sustained operationis theoretically possible. These are restricted to spe- 3 n=2 g=4 to co, to when S o n=1 9 to 1, gto etc., when S 0 geto, when S 0 It may be seen from this that the narrow speed ranges are only partially useful. WVith this fact in view the first range g=2n to 00 denotes the main speed range.

This relationship is shown in Fig. 5 wherein the ordinate represents the specific speed g and the abscissa represents the mode of operation n. The upper speed range, extending upward to infinite values of q, is bounded by the line 31. The next speed range is bounded by the lines 32 and 33. the next by the lines 34 and 35, and so on.

The main speed range represents only the possible values that g and 12 may assume. To determine for any specific case, the correct value of g for a certain mode and for certain proportions of the hammer, resort may be had to equation (33). This can be written in the following form.

The equation represents the relation between all design variables of the device, expressed more or less directly through the quantities S, 02 a and g, which must hold if sustained operation is to be obtained.

Referring to Fig. 6, the graph shown is of some of the characteristic curves of the percussive device for various conditions of operation within the main s ed range.

In this graph, the speci 0 speed 9 is represented by the abscissa and the spring function S and phase angle G are represented by the ordinates. Line 36 shows the ratio between the equivalent initial compression of the spring :0 and the amplitude of free vibration of the hammer head, which must exist in order to attain a sustained sequence of blows in the first mode, when the coefficient of rebound is zero. Line 37 shows the same relation when the coefiicient of rebound e is 20. Lines 38 and 39 show the same relations for the second mode, that is, when the force completes two cycles for each blow and lines 40 and 41 show the same relations for the third mode. Similar curves can be drawn for other modes.

To obtain the actual relations of the masses and the springs to attain these conditions it n=2 9 to 1, %to

is merely necessary to introduce the values of m and a, from equations (2) and The values of the impact or phase angle G that are obtained for the first mode of operation and for values of the coefficient of rebound of zero and two tenths are shown by the lines 42 and 43, respectively. The lines 44 and 45 show the values of G for the second mode of operation when the coefficient of rei bound is equal to zero and two tenths, and the lines 46 and 47 show these values for the third mode of operation.

The effectiveness of performance of the device is greatly dependent upon this impact angle, because the impact velocity 11 varies with the sine of this angle.

It is evident to those skilled in the art that the foregoing conclusions will hold for mechanical arrangements different from those illustrated. For example, the force F may be a function of the speed and may be produced by means other than electromagnetic coils, in which case, it is merely necessary to change the expression for (1, equation (7 The curves in Fig. 6 will remain unchanged, except for the units in which they are expressed. The particular arrangement and proportions of the various cooperating parts of the percussive device embodying the invention may be materially changed without departing from the spirit and scope of the invention as defined in the appended claims.

I claim as my invention:

1. In a percussive device, the combination with a tool-supporting anvil, of a hammer head disposed to impinge against the anvil, means for applying a periodic force to actuate the hammer head, and a member ofi'ering elastic resistance tothe motion of the hammer head away from the anvil, said elastic member and the hammer head being so pro ortioned that the hammer will 0 erate wit a stroke frequency which is a su -multiple of the periodic force. M

2. In a percussive device, the combination with a tool-supporting anvil, of a hammer head disposed to impinge against the anvil, means for applying a periodic force to actuate the hammer head, and a member offering elastic resistance to the motion of the hammer head away from the anvil, the natural frequency of the hammer head and the minimum pressure of the elastic member being proportioned in such manner that the hammer will operate when there are two or more cycles of the periodic force for each blow of the hammer head.

3. In a percussive device, the combination with a tool-supporting anvil, of an oscillating system comprising a hammer headdisposed to strike said anvil and a resilient member, and means for applying a periodic force to said hammer head to operate it, said oscillating system being so proportioned that the device will operate at a frequency difl'erent from that ofthe applied periodic force.

a. In a percussive device, the combination with a tool-supporting anvil, of an oscillating system comprising a hammer head disposed to impinge upon said anvil and a resilient member, and. means for applying a periodic force to said hammer head to cause it to oscillate. said anvil, hammer head and resilient member being so proportioned that a periodic torce having a frequency that is a harmonic of the frequency at which the oscillating system is adjusted to operate will cause the percussive device to function. v

In an electrically driven percussive device. the combination with an anvil for supporting a tool, of a solenoid for exerting periodic magnetic impulses and a mechanical oscillating system comprising a hammer head of magnctizable material that is disposed to in'ipinge upon the anvil and to constitute an armature tor the solenoid and a resilient ele ment, said oscillating system bein so proportioned that it will vibrate at the frequency of one harmonic of the impressed magnetic impulses.

6. In an electrically driven percussive de vice, the combination with a tool-supporting anvil, of an oscillating system comprising a resilient member and a hammer head of mag netizable material disposed to impinge upon the anvil and a solenoid for impressing periodic magnetic impulses upon the hammer head. said oscillating system being so proportioned that the devicewill operate when the frequency of said impulses is a multiple of the resulting frequency of vibration of the oscillating system.

7. In a percussive device, a reciprocatory hammer mass, yielding energystoring means constituting, with said mass, a. mechanical oscillating system and tending to cause said mass to strike in one direction of the reciprocal movement thereof, and means for exercising upon said mass, a cyclic force producing such reciprocal movement, the several elements of said device being so related that the device will operate when there are two or more force cycles for each hammer stroke.

8. A percussive device comprising a hammer body, a relatively stationary guide permitting motion of said body toward an ob ject to be struck and away. therefrom, yielding energy-storing means supported by said guide and pressing said body toward said object, space-energizing means producing an intermittent force causing said body to cyclically move away from said object and strikethe same, the body, the energy-storing means and the force being so related to each other that the hammer will operate when there are at least two force cycles for each hammer stroke.

' 9. A percussive device comprising a hammer body, a relatively stationary guide permitting motion of said body toward an object to be struck and away therefrom, yieldlng energy-storing means supported by said guide and pressing said body toward said object, electrical space energizing means supported by said guide and impressing upon said body a cyclical force causing the device to operate with a cyclical striking action of said body, said hammer body and energystoring means being so proportioned that the frequency of said striking action is a fraction of the force frequency.

10. In a reciprocating device, a mechanical oscillating system comprising a resilient member and a plunger of predetermined mass, a solenoid disposed to exert magnetic impulses upon the plunger and a source of alternating electric current of standard fre quency for energizing the solenoid, said oscillating system being so designed that the device will operate at a frequency of oscillation which is a sub-multiple of the frequency of the energizing alternating current.

11. In a percussive device, in combination, a tool supporting anvil, a hammer disposed to impinge upon the anvil, a resilient element disposed to exert force upon the hammer in the direction of the anvil, said hammer and resilient element comprising a mechanicaloscillating system, and means for impressing a substantially harmonic oscillating force upon the hammer, the mass of said hammer and the characteristic of said resilient element being so chosen that the hammer will operate at a frequency which is a sub-multiple of the frequency of the impressed oscillating force.

In testimony whereof, I have hereunto subscribed my name this 20th day of July, 1927 @ARL RICHARD SODERBEEG.

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