US3176962A - Jack - Google Patents

Description

R. S. BAKER A ril 6, 1965 JACK 4 Sheets-Sheet 1 Filed Sept. 30, 1965 R. S. BAKER A ril 6, 1965 JACK 4 Sheets-Sheet 2 Filed Sept. 30, 1963 INVENTOR P05 52 7 62 .Bfl/(EB Er W ATTORNEYS April 6, 1965 R. s. BAKER JACK Filed Sept. 30, 1963 4 Sheets-Sheet 2 INVENTOR fad-file r 62 BAKE-B R. S. BAKER A ril 6,. 1965 JACK 4 Sheets-$heet 2 Filed Sept I50, 1963 INVENTOR F05 5e 7- 63 34x52.

ATTORNEYS April 6, 1965 R. s. BAKER 3,176,962

JACK

Filed Sept. 30, 1963 4 Sheets-Sheet 3 ATTORNEYS a INVENTOR Q Poms-1e7- 6. 314K516 5 I United States Patent 3,176,?62 JACK Robert S. Baker, R0. Box 11476, Tampa, Fla. Filed Sept. 30, 1963, Ser. No. $12,749 it) Claims. ((11. 254-67) This invention relates to jacking devices, and more particularly to such devices of electro-mechanical nature.

While the jacking device of the present invention is suitable for use in any jacking operation, and can be utilized as a substitute mechanism wherever fluid operated cylinder jacks are called for, it is specially adapted for use as a portable jack for tightening, or tensioning, strands, cables, and like members. It is in this embodiment that the present disclosure will be made.

At the present time in this country, all jacking in connection with tensioning cables, such as required for making prestressed concrete members for example, is done by means of hydraulics. Much of this work has been done by simultaneous tensioning of a plurality of cables. Where the member to be formed was a large one, very heavy equipment was required, including motor, pumps, hydraulic lines, by-passes, high and low pressure systems, etc. Even when smaller members are made and lighter equipment is used, the many components listed above are required. Single-strand jacking is becoming increasingly popular, but in this case, also, the hydraulic equipment is cumbersome, expensive and relatively ineiiicient.

The general object of the present invention is to provide an electro-mechanical jack which is simple, economical, light weight and of highly increased efiiciency.

A more specific object is the provision of a jack of this kind which is adapted to engage, and exert a pulling force upon, strands, cables and like members to pull, remove the slack from, and/ or tension them.

Another object is to provide a jack suitable for cable tensioning which is portable and can be moved from strand to strand.

A further object is the provision of a jack which operates upon a motor-driven ball screw principle.

Still another object of the invention is to provide a jack which will give visual indication of the pulling force imposed upon a strand, or cable, so that predetermined tension may be applied to the strand irrespective of the length of the pull or the amount of slack in the strand at the outset.

Other objects of the invention will become apparent from the following description of one practical embodiment thereof, when taken with the drawings which 'accompany, and form part of, this specification.

In the drawings:

FIGURE 1 is a side view of a portable electro-mechanical jack embodying the principles of the present invention;

FIGURE 2 is a top plan view of the jack, parts being broken away to show the interior;

FIGURES 3 and 3 together constitute a vertical section through the jack;

FIGURE 4 is a vertical transverse section through the pulling head and guide tube, taken on the line l4 of FIGURE 3 FIGURE 5 is a vertical transverse section through the jack at the load indicator position, and is taken on the line 55 of FIGURE 1 FIGURE 6 is a fragmentary section taken on the line s-s of FIGURE 1, illustrating the position of a limit switch;

FIGURE 7 is a fragmentary section through the gear casing, taken on the line 7-7 of FKGURE 3 and FIGURE 8 is a fragmentary section taken on the line 8-8 of FIGURE 4, showing the means employed to ob- 3,.l'i6,%2 Patented Apr. 6, 1965 tain a visual indication of the pulling force applied to a strand engaged by the jack.

In general, the jack is a unitary tool, in which a motor is used to cause a ball screw to move axially and draw a pulling head linearly of the device relative to a head guide which acts as an abutment member. The guide is made in two sections with compressible members between the sections, to provide for relative movement between the sections under load and actuation of a load indicator. Means are also provided to show the extent of relative movement between the head and head guide.

Referring to the drawings in detail, the jack is shown as including an elongated body 1, a gear casing 2, an electric motor 3, and a combination stand and handling frame 4.

The body 1 is composed for the greater part of its length of a guide 5, having a forward section 6 and a rear section '7. The two sections have annular flanges 8 and 9 at their adjacent ends, and are coupled in long'tudinal alignment by bolts 10. Belleville spring units 11 are mounted on the shanks of bolts 10, and seat in recesses 12 and 13 in the respective flanges 8 and 9. The bolts are drawn up evenly to place the Belleville units under a desired predetermined compression. The purpose of the springs and their action will be described later.

Guide 5 is substantially U-shaped in cross-section, being open along the full extent of its top. The open top provides a slot 14 along which an indicator (to be described) may move. It also allows free access to the pulling head for engaging and disengaging cable. The outer end of the guide, that is the end farthest trom the gear casing 2, is bridged by an abutment plate 15, welded around its edges to the sides and bottom of the guide 5. The plate is notched from its top edge to below the center of the guide to provide an entrance notch 16 for cable to be tensioned. The guide is strengthened along its upper edges at the side of slot 14 by means of rods 17 extending throughout the length of each of the sections of the guide. The rods are welded to the guide walls along their full lengths.

The back end of section 7 of the guide fits within a recessed seat 18 in a cap assembly 19 and is welded in place. The opposite side of the cap has an annular projection 20 about which a cylindrical housing member 21 fits. The cap and housing member have matching flanges 22 and 23 and are bolted together. Cap 19 ha another recessed seat 24 in its face opposite seat 18 to receive a bearing 25. The cylindrical housing member is also recessed in its end, as at 26, to seat a bearing 27. Bearing 25 serves as an end thrust bearing under load, while hearing 27 receives the hub of a gear 28. The gear hub fits over the end of a ball-bearing nut 29 which has its other end mounted in a ring 3! seated in a bearing 31 carried by the housing member 21.

Gear 28 is fixed to the nut 29 and is driven by a spur gear 32 mounted on shaft 33 of motor 3. The motor is bolted to a motor platform 34 carried by the cap 19. The gears 28 and 32 are enclosed within casing 2 for protection of the gears and operators of the jack.

The gear casing has a rearwardly projecting sleeve 35 which supports a ring 36. This ring has a collar 37 to which is attached one end of a collapsible boot 38.

Mounted within the nut 29 is a ball-bearing screw 39. The screw extends through the nut and along guide 5 in a forward direction. It projects to the rear into boot 38, and has a projection 40 at its rear end to which the outer end of the boot is connected. As the screw moves to the rear, boot 38 will extend, and when the screw moves in an opposite direction the boot contracts, or collapses.

Screw 39 and nut 23 are a ball-bearing unit of well known type. The nut has thread-like grooves 41 on its inner face, and a plurality of balls 42 run in the threads and 27.

At the forward end of the screw 39 there is a pulling head 45, which is threaded onto a forwardly projecting threaded stud 46 of the screw 39. The head is U-shaped in cross-section, being open at the top, and carriesa plate 47 at its forward end. The plate is notched from its upper edge to provide a cable slot 48. Spaced'from the end plate 47, a baffle 49 inclines from the head bottom rearwardly. The area from the end plate 47 to the baffie forms a seat for cable anchors fitted about the ends of cables to be tensioned.

At the back end of the pulling head, there is a pointer 50 which is screwed to the head. The pointer moves over a scale 51 marked along the top edge of guide 5, adjacent one edge of slot 14.. As the head moves along the guide, the distance travelled will be indicated by the position of the pointer on the scale.

In order to protect the screw 39, and other internal 'parts of the device, from dirt, and yet permit free movement of the pointer over the guide upper edge, a flexible cover 52 extends over the slot. The flexible cover also permits exit and entry of cable and anchor at any convenient position. The cover is attached to the opposite side of the guide from that carrying scale 51 by means of angle brackets 53.

The jack stand, or handling frame, 4 is composed essentially of a U-shaped main frame 54 having its bridge underlying the guide tube of the jack body, and the ends of its legs secured to the forward face of the gear casing 2. A leg 55 projects downwardly from the center of the bridge directly below the guide 5. 'Leg 55 together with a flattened base 56 on the gear casing 2 provide surface I contacting members to support the jack. The jack can be lifted and transported, or otherwise handled by means of this stand. If desired, a lifting device can be connected toeyes 57 attached to the frame.

It is desired that the pulling force exerted on a a cable be known at all times, and, to this end, the jack carries a pressure indicator 58, mounted on a bracket 59', secured to the rear section 7 of the guide 5. An operating rod 60 extends forwardly from the indicator through openings 61 and 62 in the guide flanges 9 and 8, respectively. A set screw 63 fixedly connects the operating rod in the flange 8 of the forward section 6 of guide 5. With this arrangement, any force which causes. compression of the Belleville units between flanges 8 and 9 will cause the op' erating rod 60 to move relative to the indicator 53, with the result that the indicator will show the force requiredto cause the movement. The indicator will have its face ex- A posed through an opening 64in a'housing member 65 connected to an extension 66 at the top of the guide section 7 adjacent the flange 9. The bottom edge of the housing will be hooked under the adjacent leg of'the U-frame 54 of the stand.

The motor 3 will be a reversible one and will be controlled by a switch 67 located on the motor. If desired, limits switches 68 and 69 may be used to prevent travel of the screw 39 beyond predetermined limits. Switch ss can be mounted on a gusset plate 75) beneath the motor platform 34, and have its trip arm 71 contacted, and actuated, by the pointer 50 when the pulling head has reached its limit of movement in a pulling direction. Switch 65 is shown mounted in the sleeve projecting from the gear casing. Its trip arm 72 may be contacted by the screw extension 40, or any other convenient part of the screw assembly to stop reverse movement of the screw whenthe 4 pulling head is in proper position for engaging a cable for tensioning.

In operating the device, the jack will be positioned with its outer end in abutment with a bolster plate of a form in which a prestressed concrete member is to be made. The jackwill be set in alignment with a cable strung along the form bed and through the bolster plate. The extended end of the cable will lie in the notch 16 of the abutment plate 15, and project through the cable slot 48 at the end of pulling head 45 with its end lying within the pulling head. A suitable anchor is positioned on the cable end.

Motor 3 will be started, and this will rotate gears 32 and 28, and through them ball-bearing nut 29, to cause screw 3? to move through the nut and the pulling headto move away from the forward'end of the jack body. The

anchor on the cable end will contact the plate 47 of the pulling head so that the pulling head will draw the cable with it, first removing the slack from the cable and then tensioning the cable.

It will be apparent that the pulling force of the head is applied through the screw to the ball-bearing nut, and from the nut through the jack body against the member with which the body end is in abutment. Thus, the two points of pressure are the nut and the body end which are on opposite sides of the body coupling at the flanges 8 and 9 with the result that all of the force is applied through the Belleville spring units.

There will be relatively little pressure applied during the initial taking up of slack, and the strength and the initial compression of the springs through tightening of bolts 10, will be such that there will be no movement of the springs and no pressure indication on the indicator 58. During the period of slack take up, the pointer 50 will have travelled a distance over the scale 51 equal to the travel of the pulling head. This point should be noted, as specifications for prestressed concrete members frequently require that cables be tensioned by a predetermined degree of elongation. Having noted the reading on'scale 51 at the end of slack take up, the cable elongation can be accurately made.

After removing slack, continued movement of the pulling head first places the cable under tension, then progressively increases that tension. The extent of elongation can be precisely checked by scale 51, and indicator 58 will provide continuous visual indication of the pull being applied to the cable. When the required cable elongation and pulling force have been achieved, the motor will be stopped. An anchor on the cable can be brought up close to the bolster plate against which the jack abuts to hold the cable fast in the head under desired tension. The motor can then be reversed to run the pulling head back to its starting position.' As the head starts back, the cable end will contact the inclined bafile 49 and ride up it to be released from the head. When the pulling head reaches its position of rest, switch 69 will be actuated to break the motor circuit. The jack is then free for movement to the next cable position.

The jack disclosed herein is readily moved from place to place, and is a single unitary tool. The use of a ballbearing screw as the power transmission member permits extremely heavy pulls with low power output. Forming the body in two parts with Belleville spring units intervening, so that the springs become a part of the thrust column, permits a single continuous pulling operation to first take up slack, then tension, yet allows for measurement of only the force applied during tensioning. This is accomplished by connecting the indicator and its operating rod to members opposite sides of the Belleville units. At the same time, the linear movement of each pulling operation is indicated automatically.

While in the above one practical embodiment of the invention has been disclosed, it will be apparent that the particular structure shown and described is only for purposes of illustration, and the invention may take other forms within the scope of the appended claims.

What is claimed is:

1. A jacking device comprising, a body, a portion of the body forming an elongated guide having a free end forming an abutment, a pulling head slidable in the guide, a screw attached to the pulling head, a nut rotatably mounted in the body and threaded upon the screw, the nut being fixed against bodily movement relative to the body in the direction in which the pulling head is slidable, and means to rotate the nut including a motor mounted on the body and interconnecting the motor and nut to move the pulling head along the guide, the frame having side rails by which the jacking device can be handled and a leg to support the jacking device on the ground.

2. A jacking device as claimed in claim 1, wherein the pulling head carries a pointer, and there is a scale along the guide over which the pointer moves when the pulling head is advanced along the guide to indicate the distance travelled by the pulling head.

3. A jacking device comprising, a body including an elongated guide, the body being of two sections arranged end to end, compressible means positioned intermediate the body sections to yieldingly separate the sections, means connecting the sections in alignment, one body section having a free end forming an abutment, the other body section having a nut rotatable therein and held against bodily movement, a pulling head slidable in the guide and having means to engage a member to be tensioned, a screw connected to the pulling head and threaded through the nut, means to rotate the nut to draw the pulling head from the abutment end of the said one body section, a pressure gauge mounted on one of the body sections and having an operating rod attached to the other of said body sections, whereby rotation of the nut will draw the pulling head having a member to be tensioned connected thereby away from the abutment end and impose a pressure upon the abutment end through the compressible means and thereby actuate the pressure gauge to provide visual indication of the tension applied to the member to be tensioned.

4. A jacking device as claimed in claim 3, wherein there is a pointer carried by the pulling head and a scale on the guide over which the pointer moves as the pulling head is drawn from the abutment end to indicate the distance the pulling head is moved.

5. A jacking device as claimed in claim 3, wherein the means to rotate the nut includes a motor mounted on the section of the body carrying the nut, and power transmitting means between the motor and the nut.

6. A jacking device as claimed in claim 5, wherein there is a frame connected to that section of the body carrying the nut, the frame including side rails by means of which the device can be handled and a leg to support the device on the ground.

7. A jacking device as claimed in claim 3, wherein there is means to adjust the initial pressure on the compressible means.

8. A jacking device as claimed in claim 3, wherein the compressible means are Belleville springs.

9. A jacking device as claimed in claim 8, wherein the means connecting the body sections in alignment includes means for adjusting the initial pressure on the Belleville springs.

10. A jacking device comprising, a body of two sections arranged end to end, compressible means positioned intermediate the body sections to yieldingly separate the sections, means connecting the sections in alignment, one body section having a free end forming an abutment, the other body section having a nut rotatable therein and held against bodily movement, a screw connected to the pulling head and threaded through the nut and having means carried thereby to engage a member to be tensioned, means to rotate the nut to draw the screw from the abutment end of said one body section, a pressure gauge mounted on one of the body sections and having an operating means attached to the other of said body sections, whereby rotation of the nut will draw the screw having a member to be tensioned connected thereto away from the abutment end and impose a pressure upon the abutment end through the compressible means and thereby actuate the pressure gauge to provide visual indication of the tension applied to the member to be tensioned.

' WILLIAM FELDMAN, Primary Examiner.

MILTON S. MEHR, Examiner.

Claims (1)

1. A JACKING DEVICE COMPRISING, A BODY, A PORTION OF THE BODY FORMING AN ELONGATED GUIDE HAVING A FREE END FORMING AN ABUTMENT, A PULLING HEAD SLIDABLE IN THE GUIDE, A SCREW ATTACHED TO THE PULLING HEAD, A NUT ROTATABLY MOUNTED IN THE BODY AND THREADED UPON THE SCREW, THE NUT BEING FIXED AGAINST BODILY MOVEMENT RELATIVE TO THE BODY IN THE DIRECTION IN WHICH THE PULLING HEAD IS SLIDABLE, AND MEANS TO ROTATE THE NUT INCLUDING A MOTOR MOUNTED ON THE BODY AND INTERCONNECTING THE MOTOR AND NUT TO MOVE THE PULLING HEAD ALONG THE GUIDE, THE FRAME HAVING SIDE RAILS BY WHICH THE JACKING DEVICE CAN BE HANDLED AND A LEG TO SUPPORT THE JACKING DEVICE ON THE GROUND.

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