POWER NUTRUNNER WITH SHUT-OFF

Abstract: A power nutrunner comprising a planetary reduction gearing (12) and a torque limiting release clutch (13) disposed between a ring gear (25) and the tool housing (11), wherein the ring gear (25) is tubular in shape and having an outer annular shoulder (41) at its one end carrying cam teeth (42) for cooperation with a spring biassed thrust element (45) via balls (43) and cam surface (44). The thrust element (45) encircles the ring gear (25) and is rotationally locked relative to the housing (11) via a ball spline connection (47-49). A clutch release and signal producing Reed relay (58) is coupled to the ring gear (25) by means of a pivoting lever (59) carrying one of a pair of permanent magnets (71, 72) for activating the Reed relay.

Description: Power nutrunner with shut-off. This invention relates to a power nutrunner with an electrically operated power supply means for accomplishing an automatic power shut-off. In particular, the invention concerns a power nutrunner comprising a planetary reduction gearing, a torque responsive release clutch with a movable element for displacement at release of the clutch, and a release detecting and signal producing means connected to the movable clutch element and communicating with the power supply means. A power nutrunner of this type is described in British Patent No. 2 002 665. This prior art power nutrunner comprises a rotation motor, a planetary reduction gearing, a torque responsive release clutch associated with the reduction gearing, and a release detecting and signal producing means connected to the clutch and communicating with the power supply means. See Fig. 7. A signal produced at release of the clutch initiates shut-off of the nutrunner motor. In this known tool, there is used a mechanically activated micro switch for accomplishing the release responsive signals. This arrangement is found to be less satisfactory in that micro switches are not able to withstand that great number of very fast and abrupt activations which result from the clutch releases at hundred thousend tightening processes or more for which the tool is intended. For heavy-duty tools used in industry, there is required an extremely high reliability and accuracy. This could not be satisfied by this known tool comprising the illustrated release and signal producing means. In more general terms, it is to be observed that micro switches with their internal "flip-flop"-type bistable mechanism are very sensitive to at least three kinds of external influence, namely I) mechanical shock, II) too fast activation, and III) contamination by for instance oil, grease, wear particles etc. Mechanical shock is mainly caused by the return strokes. A fast activation and a very quick response to the clutch release is required. At a normal rotation speed of the clutcn of about 600 rp and with a distance of 1/3 revolution to the next impact of the clutch, there is about 0,03 seconds available for accomplishing initiation of a shut-off signal. One can not afford to loose more than 5% to get the signal, i.e. 0,0015 seconds. This is very difficult for a micro switch to cope with. There has been a problem for a long time to find good and durable enough switches or signal producing means to be used n power nutrunners. Touch-free inductive displacement detectors, for example, are not exposed to mecnanical wear in the same way as micro switches, but they require relative long activation movements and are not accurate and fast enough to be suitable for the tool shut-off purpose. The problem solved by the invention is to provide a power nutrunner of the above related type with a durable, accurate and compact release detecting and signal producing means such that an accurate and fast enough power shut-off of the tool could be guaranteed for a great number of tightening processes. Other obiects and advantages of the invention will appear from the following specification and claims. A preferred embodiment of the invention is below described in detail with reference to the accompanying drawing. On the drawing: Fig 1 shows a longitudinal section through the front part of a power nutrunner according to the invention. Fig 2 shows a fractional section through the power nutrunner shown in Fig 1, but located in a different plane. Fig 3 shows a side elevation of the release clutch included in the power nutrunner shown in Fig 1. Fig 4 shows, on a larger scale, a detail view of the release detecting and signal producing device. Fig 5 shows a section taken along line V-V in Fig 4. The nutrunner illustrated in tne drawing figures comprises a motor unit 10 the forward end portion only of which is shown in Fig 1. Since the motor unit 10 does not form any part of the invention a detailed description thereof is not needed and is, therefore, left out of this specification. To the motor unit 10 there is bolted a housing 11 for a reduction gearing 12 and a torque limiting release clutch 13. An output spindle 14 is connected to the motor unit 10 via the reduction gearing 12 and is provided with a chuck 15 for attachment of a screw joint engaging tool implement. At its forward end, the housing 11 is provided with an end wall 16 in which the output spindle 14 is rotationally journalled. The end wall 16 is formed with an internal neck portion 17 for providing a proper guidance for the output spindle 14. A bushing 18 at the front end of the end wall 16 forms a bearing for the output spindle 14 and is formed with an annular shoulder for transferring axial forces from the spindle 14 to the housing 11. A lock ring 19 and a shock absorbing resilient ring 20 are mounted on the spindle 14 for engagement with the shoulder of the bushing 18. In the opposite direction, the spindle 14 is axially locked by a lock ring 21 cooperating with the inner end of the end wall neck portion 17. The rear end of the housing 11 comprises an end wall 22 which is secured to the motor unit 10 by means of screws 23. The end wall 22 is formed with a ball race 24 for rotational support of a tubular ring gear 25 via a number of balls 26 in cooperation with a ball race 27 on the ring gear 25. The reduction gearing 12 comprises two consecutive planetary gearings for which the ring gear 25 is a common member. The planetary gearings comprise a sun gear 28 attached to the motor unit output shaft 29, a first set of planet wheels 30, a planet wheel carrier 31 formed integrally with a second sun gear 32, a second set of planet wheels 33, and a second planet wheel carrier 34 connected to the output spindle 14. The planetary gearings are axially confined between two end washers 35, 36 supported by two lock rings 37, 38 secured to the ring gear 25. The ring gear 25 is substantially tubular in shape and has an outer cylindrical surface 40 and an annular shoulder 41. See Fig 3. This shoulder 41 is provided with three axially directed and equally spaced cam teeth 42 which together with three balls 43 and three corresponding cam surfaces 44 on an annular thrust element 45 form the torque transferring clutch 13. These cam surfaces 44 are formed by three indentations 46 in the rear annular end surface of the thrust element 45. See Fig 3. The thrust element 45 is axially movable in the housing 11 but locked against rotation by means of a ball spline connection. The latter comprises three axially directed grooves 47 disposed on the outside of the thrust element 45, three slots 48 in the housing 11, and three balls 49 engaging the grooves 47 and the slots 48. A circular band 50 on the outside of the housing 11 retained by a lock ring 51 covers the slots 48, thereby preventing the balls 48 from falling out. The balls 49 are inserted from the outside of the housing 11 after removal of the lock ring 51 and sliding aside the band 50. As illustrated in the drawing figures, the thrust element 45 has a larger diameter than the outer cylindrical surface 40 and encircles the latter. Accordingly, the thrust element 45 is located outside the ring gear 25 as is the rear end portion of a compression spring 53 which acts between the thrust element 45 and an adjustable support member 52 at the front end of the housing 11. The force developed by the spring 53 on the thrust element 45 exerts a bias load on the release clutch 13. This adjustable bias load together with the very shapes of the cam surfaces 44 and cam teeth 42 are determining for the torque level where the clutch releases. At its rear periphery, the ring gear 25 is provided with three radially extending pins 55 disposes at equal angular distances from each other. In . an aperture 56 in the housing 11 there is movably supported a ball 57, and on the outside of the housing 11 there is mounted a release detecting and signal producing Reed relay 58. A leaf metal lever 59 is provided with a central opening 54 which together with a fixed stud 60 forms a fulcrum for the lever 59. The lever 59 is pivoted on the stud 60 to transfer an activation movement from the ball 57 to the Reed relay 58. A spring 61 exerts a bias force on the lever 59. The Reed relay comprises a contact unit 62 and an activator 63. The contact unit 62 consists of two leaf metal contact tongues 64, 65 which are rigidly mounted in a hollow body 66 of an insulating material, for instance glass, and having their inner ends overlapping each other. The glass body 66 is rigidly attached by gluing to a mounting plate 67 which is secured to the housing 10. At their outer ends, the contact tongues 64, 65 are connected to wires 68, 69 for communication with an electronic power supply and control means by which the operation of the nutrunner is controlled. This control means do not form any part of this invention and is, therefore, not described any further in this specification. The activator 63 of the Reed relay comprises two permanent magnets 71, 72, one of which 71 is rigidly attached to the body 66, whereas the other one 72 is mounted on the outer end of the lever 59. This movable magnet 72 is received in a through opening 73 in the plate 67. In its unactivated condition, the Reed relay 58 is influenced by both of its two activator magnets 71, 72, such that the contact tongues 64, 65 are balanced relative to each other in an open condition, as illustrated in Fig 5. However, as the clutch 13 releases and one of the pins 55 engages the ball 57, the lever 59 is pivoted about the fulcrum stud 60 lifting the magnet 72 away from the contact unit 62. Then, the balance between the magnetic forces acting on the contact tongues 64, 65 is changed and the tongues 64, 65 are shifted to a closed contact condition. Thereby, a clutch release detecting signal is created. In operation of the nutrunner, the output spindle 14 is connected to a screw joint to be tightened via the chuck 15 and a tool implement attached thereto. Rotation power is supplied from the motor unit 10 via the shaft 29, and a speed reduction is obtained by the two consecutive planetary gearings before the rotation power reaches the output spindle 14. As the torque resistance from the screw joint increases, the reaction torque from the planetary gearings increases on the ring gear 25. This means that the ring gear 25 tends to start rotating, but is prevented from that by the clutch 13. The ring gear 25 remains stationary and the clutch continues to transfer the reaction torque from the ring gear 25 to the housing 11 as long as the bias load of the spring 53 is able to prevent the thrust element 45 from moving axially as a result of the interaction of the cam teeth 42, the balls 43 and cam surfaces 44. As the intended release torque level of the clutch 13 is reached, however, the spring 53 yields to a point where the cam teeth 42 are able to pass over the balls 43 and the ring gear 25 is free to rotate relative to the thrust element 45 and the housing 11. The balls 43 remain in the indentations 46 in the thrust element 45 during the relative rotation between the ring gear 25 and the thrust element 45. At rotation of the ring gear 25, at release point of the clutch 13, one of the pins 55 comes into engagement with the ball 57 to move the latter outwardly. This activation movement is transferred via the lever 59 to the Reed relay 58 which delivers an electric signal to a control means for accomplishing shut-off of the nutrunner motor. Each of the pins 55 is so located in relation to the cam teeth 42 that an activation of the Reed relay 58 via the ball 57 and the lever 59 does not take place until the teeth 42 have reached or just passed the top of the balls 43, i.e. when the torque transfer through the clutch has just ceased. Depending on the actual rotational speed of the nutrunner motor and the other rotating parts of the tool at the shut- off point, the ring gear 20 continues to rotate some distance before coming to stand still. If the speed is high at the release point of the clutch 13, which is the case at tightening so called stiff screw joints, the ring gear cam teeth 42 will reach and even pass over the next ball engaging position before stopping. Since the motor is shut off at the first release position of the clutch, there is no driving torque to be transferred in the second ball engaging position of the gear ring 20, also is the kinetic energy of the rotating parts substantially decreased, which means that the second clutch engagement, if any, does not cause any torque overshoot. The above described nutrunner is intended to be powered by an electric motor with the Reed relay connected to a motor voltage controlling means of any suitable kind. In particular, the invention is suitable for application on a battery powered nutrunner. In such a case, the motor control means is located on-board the tool. However, the invention is not limited to a nutrunner having an electric motor, but could as well be applied on a nutrunner having a pneumatic motor. In such a case, the Reed relay is connected to an external electric control unit by which a pressure air supply valve is controlled so as to obtain a timely shut-off of the motor at release of the clutch 13.

Claims: Claims . 1. Power nut runner, comprising a housing (11), a rotation motor (10), an output spindle (14), an electrically operated power supply means connected to said motor (11), a planetary type reduction gearing (12) and a torque responsive release clutch (13) disposed between said motor (11) and said output spindle (14) and including a movable element (25) which is subjected to a certain displacement at release of said clutch (13), and a release detecting and signal producing means (58) connected to said movable clutch element (25) and communicating with said power supply means, c h a r a c t e r i z e d by an activating means ( 55-59 ) supported in said housing (11) and engageable with said movable clutch element (25), said release detecting and signal producing means (58) comprises a Reed relay including a contact unit (62) rigidly attached to said housing (11) and a shiftable magnetic activator (63), said contact unit (62) being ≤witchable between a first condition and a second condition, said activator (63) being operably associated with said activating means (55-59) so as to accomplish a switching of said contact unit (62) from said first condition to said second condition to, thereby, produce an electric signal at release of said clutch (13) . 2. Power nut runner according to claim 1, wherein said magnetic activator (63) comprises two oppositely disposed permanent magnets (71,72) arranged to balance said contact unit (62) in said first condition, whereby one of said magnets (71) is rigidly attached to said housing (11), whereas the other one of said magnets (72) is attached to said activation means (55-59), whereby, at release of said clutch (13), said other one of said magnets (72) is displaced in relation to said contact unit (62), thereby causing said contact unit (62) to switch to said second condition. 3. Power nut runner according to claim 2, wherein said activating means (55-59) comprises a double-armed lever (59) pivotably supported on a fulcrum (54,60) on said housing (11) and carrying at its one end said one of said magnets (72) and being connected by its other end to said movable clutch element (25) . 4. Power nut runner according to claim 3, said lever (59) comprises a metal leaf having a central opening (54) intended to receive with a loose fit a fixed stud (60), whereby said opening (54) and said stud (60) form said fulcrum. 5. Power nut runner according to anyone of claims 1- 4, wherein said movable clutch element (25) is formed by a ring gear of said planetary reduction gearing (12), said ring gear (25) is rotationally supported in said housing (11) • 6. Power nut runner according to anyone of claims 1-5, wherein said motor (10) is an electric motor.

Inventors: HANSSON CHRISTER GUNNAR, RAHM ROLAND ERIK, HANSSON, CHRISTER, GUNNAR, RAHM, ROLAND, ERIK
Applicants: ATLAS COPCO TOOLS AB, HANSSON CHRISTER GUNNAR, RAHM ROLAND ERIK, HANSSON, CHRISTER, GUNNAR, RAHM, ROLAND, ERIK
Application year: 1997
Main classification: B25B23
IPC codes: B25B23, F16D43