WO1994013979A1

WO1994013979A1 - Power gear assembly

Info

Publication number: WO1994013979A1
Application number: PCT/CZ1993/000029
Authority: WO
Inventors: Jirí TRBUSEK
Original assignee: Licexia, Spolecnost S Rucením Omezenym
Priority date: 1992-12-08
Filing date: 1993-12-06
Publication date: 1994-06-23
Also published as: CN1092347A; AU6653294A

Abstract

For a control of machine-tool feeds, in particular reciprocating feeds, there is designed a power gear assembly comprising a first driving member, which is coupled with basic drive means and a second driving member, which is coupled with second drive means for producing a rotation of the second driving member with respect to the first driving member. The first and the second driving members comprise a motion screw (1) and a nut (2). The nut (2) is coupled with the second drive means by a gearing having one wheel engaged with a guiding rod (12) which is coupled to the second drive means, the wheel being seated on the guiding rod (12) displaceably. The second drive means engages with the basic drive means by means of at least one pair of non-slip gears, the gears of the said pair being intercoupled by a releasable clutch (25, 35, 45).

Description

POVER GEAR ASSEMBLY

Technical Field

The invention relates to a power qear assembly producing motion of a mass element, preferably a reclprocating movement, the assembly being equipped with at least two mutually rotatably arranged members, the one of which, as a driving member, being coupled with basic drive means generating its rotation with respect to the other members

Background of the Invention

There exists a wide range of equipments and devices for producing a reciprocating motion of a mass element e.g. a movement of a table or a traversing saddle of a machine-tool, including a standard crank mechanism, oscillating link mechanism, screw-and-nut steering dear, planet gearing, friction gears of various types and constructions and their combinations, various pneumatic and hydraulic systems working on a principle of a "cylinder-plunger" unit, rotating electric, pneumatic hydraulic systems completed with a "rack-and-pinion" type gear, further linear electric motors, or electromagnetic systems based on the principle of a coil and a core and a variety of combinations of such systems

All these systems manifest several disadvantages including coarse regulation of displacement and feed rate, pre-given relationship between the backward and the forward movement Pneumatic and hydraulic systems present problems due to a leakage of presure piping and valves. heating-up and sensitivity for contaminants, especially in controlled gates. Nevertheless the maior disadvantage of all the present systems is obviously the necessary reversing of a driving power unit for achieving a change of the current sense of the created motion. Each reveising is accompanied by a significant mechanical stress and a great loss of energy resulting from braking and conseguent run-up of inertia mass of all rotating parts of the power unit and coupled driven mechanisms or engaging machine components upon the requested speed. The greater the output and operational speed and the shorter the desired reversation speed, the greater are resulting stress and losses.

Disclosure and Object of the Invention

The foregoing problems are solved by a power gear assembly in accordance with the present invention comprising at least two mutually rotatably arranged members. including a first driving member, which is coupled with basic drive means generating its rotation with respect to the other members, and a second driving member, which is coupled with second drive means for producing a rotation of the second driving member with respect to the first driving member. Further in accordance with the present invention both the first and the second driving members, each of them individually, engage with the appropriate drive means through a non-slip gear. Still further in accordance with the invention the second drive means comprises an output shaft engaging with an output shaft of the basic drive means by means of at least one pair of non-slip gears, the gears of the said pair being intercoupled by a releaseable clutch. In a preferred embodiment the first driving member and the second driving member comprise a motion screw and a nut respectively. In this embodiment the nut is preferably coupled with the second drive means by a gearing, having one toothed wheel engaged with a guide rod which is coupled to an output shaft of the second drive means, the toothed wheel being seated on the guide rod displaceably. Another preferred embodiment comprise a planetary gearing with a central wheel providing for the first driving member and a crown wheel serving as the second driving member, while a carrier provides for a driven member. Still further in accordance with the invention both the basic and the second drive means are connected to the same supply and control unit to which there is also connected at least one of the releasable clutches.

It is an obiect of the invention to eliminate speed reversal of the power gear assembly, comprising the first and the second driving members and their drive means, and to simplify the control of forward and back- ward movements of a mass element. The two independent driving power units provide for independent control of rotation speeds of both driving members. Their speeds being equal give a standstill of the mass element, any difference in both speeds results in a motion the sense or direction of which depends upon the fact, which speed is higher and which one is lower. The feed rate is directly proportional to a difference between the rotation speed of the first and the second driving members respectively. In any case, both these members rotate in the same direction, the sense of which remains the same and the direction and the speed of the mass element feed change with respect to a relative change of rotation speeds of both driving members. This feature reduces the load of drive means by inertia moments which is a remarkable feature especially in reference to applications of high outputs with high operational feed rate. It is a further object of this invention to reduce mechanical impacts during reversals undesirably influencing wear of machines. It is still a further object of the invention to minimize the load of power units, decrease starting current of applied electric motors and so simultaneously decrease the heat, load of the motors and the power consumption. According to a further aspect of the invention there is increased a control range of the governed mass element motion, especially with fine feeds as the mass element moves only when speeds of the first and the second driving members are not equal, regardless of the absolute value of their respective speeds of rotation. Driving devices, especially electric motors can be thus performed in the range of an optimal operation speed at which they display the highest efficiency, just to the contrary to prior systems by which the feed rate in the final period has to go down so far that the driving motors operate outside their optimal performance range. All the above mentioned features of the assembly in accordance with the present invention improve dynamic characteristics of the drives and decrease their power consumption. Mechanical linkage of both driving members by means of non-slip gears with various speed ratios provides for higher operational reliability, particularly in a setting and holding of the mass element standstill and safe fine feed to the preset possition. The said assembly equipped with a suitable feed sensor, e.g incremental linear sensor, is at a defined fine feed speed able to stop the mass element motion at the pre-programmed point on the feed track. According this aspect of the invention there is provided a power gear assembly comparable with costly complicated drives although it is furnished only with simple drives such as a standard asynchronous squirrelcage motor supplied from a converter with a variable output frequency. The said power gear assembly in one of the prefered embodimments maintains all properties and advantages of the screw-and-nut device, especially the power transfer capability in the axial direction of the screw shaft. Rigid mechanical linkage of the screw and the nut defining their relative movement enables to place the appropriate drive means outside the area of the mass element feed. It makes possible to utilise even belt drives. Both the first and the second driving members, either the screw and the nut, or the central and the crown wheels, can engage with the relevant drive means also by means of systems operating on the principle of an electric or elertromagnetic linkage, e.g. a synchronous induction clutch. Both preferred embodiments can be furnished with devices devices, anahling them to perform either a straight-line 5 in a rotational motion of a mass element

Brief Description of the Drawings

By way of examples the invention will be now described with reference to the accompanying drawing Fig 1 schematic-ally illustrates the principle of the invention by means of the first preferred embodiment comprising a motion screw and a nut, where the nut and its drive means are designed as a single unit. Fig. 2 represents an alternative arrangement of the first preferred embodiment with drive means of both the screw and the nut mounted unmobile. Fig. 3 shows the same embodiment of the invention as presented in Fig. 2, but completed with disengageable coupling of both rotating driving members, Fig. 4 offers, speed characteristics of the first and the second driving members. Fιg. 5 schematically illustrates another preferred embodiment comprising a planetary gearing. Fig 6 presents the embodiment with the planetary gearing having different coupling of the crown wheel with appropriate driving means and Fig 7 presents the embodiment with the planetary gearing furnished with the same coupling means as shown in Fig 3.

Description of Preferred Embodiments

Referring to Fig 1, there is shown an embodiment of the power gear assembly with the first and the second driving members comprising a motion screw 1 and a nut 2 respectively The said motion screw 1 is coupled with basic drive means including a first electric motor 3 and a supply and control unit 4. An output shaft 5 of the first electric motor 3 is arranged co-axially with the motion screw 1. The nut 2 is directly coupled with second drive means including a second electric motor 7 and the supply and control unit 4 . However each of the electric motors 3.7 is connected to a separate output of the supply and control unit 4. An output shaft 6 of the second electric motor 7 is co-axial with the nut 2 and thus with the output shaft 5 of the first electric motor 3 as well. The nut 2 together with the second electric motor 7 are supported on ball bearings mounted in a housing 8, which is slidably seated in guiding means 9 and rigidly jointed with the mass element 10. The motion screw 1 is stationary and only the nut 2 carrying the mass element 10 executes a motion in space. The mass element 10 represents e.g. a saddle of a machine tool, carying table of a planning machine etc. The assembly works principaly in the same way even in a so called kinematic reverse embodiment, when the mass element 10 is carried by the motion screw 1 and the nut 2 is stationary. The said supply and control unit 4 includes two controlled frequency converters, independent of each other, supplying their respective electric motors 3.7.

When starting both electric motors 3.7 at the same speed, the difference of the rotation speed of the motion screw 1 and the nut 2 respectively, equals zero and the mass element 10 is in a standstill. Any change in the supply and control unit 4 output freguencies results in a difference between rotation speeds of both rotating devices, i.e. the motion screw 1 rotation speed ns and the nut 2 rotation speed n_m, and the mass element 10 starts to move in either of the directions, depending to the speed, which is higher. The speed with which the mass element 10 displacemnt is performed is directly proportional to the difference between both rotation speeds n_s, n_m- Generally speeking the speed of the moving mass element 10 equals to a product of a difference of the motion screw 1 rotation speed n_s and the nut 2 rotation speed iim and the motion screw 1 thread lead. The effect of changes in both rotation speeds n_s, n_m follows from Fig. 4 . Within the first time interval T0 - T1 the motion screw 1 rotation speed unequal s the nut 2 rotation speed iim and the mass element 10 stands still. In the time interval T1 - T2 the motion screw 1 rotation speed n_s gradually goes up and the nut 2 rotation speed iini decreases and the mass element 10 starts to move left. Its final steady straight-motion speed in the time interval T2 - T3 shall be directly proportional to the. sum of changes of both rotation speeds. In the next time interval T3 - T4 the mass element 10 speed gradually slows down and equals zero at the moment T4, when the motion screw 1 rotation speed n_s and the nut 2 rotation speed n_m are equal. During the following time interval T4 - T5 the motion screw 1 rotation speed its, further decreases and on the contrary the nut 2 rotation speed nm goes up and the mass element 10 now moves right. This steady straight-motion speed in the time interval T5 - T6 shall be again directly proportional to the sum of changes of rotation speeds n_s, n_m of both rotating devices. In the next time interval T6 - T7 the mass element10 straight-motion speed decelerates because the difference between the rotation speeds n_s, n_m of the motion screw 1 and the nut 2 decreases. In the time interval T7 - T8 the mass element 10 continues its; movement in the same direction, i.e. to the right, at a slow speed, in a so called fine finishing speed At the time point T9 the motion screw 1 rotation speed n_s and the nut 2 rotation speed n_m are equal and therefore the mass element 10 is again in a standstill. The control of the movement of the nut 2 and together engaging mass element 10, including reversals, can be thus easily performed by a simple change of respective rotation speed, in the described case executed through changes of supply freguencies for both drives, no matter if there are changed both speeds simultaneously or lust any of them, as described above. Nevertheless the simultaneous change of the speeds of both electric motors 3,7 results in a feed rate which doubles the rate achived by a change of only one of the speeds.

Similarly to the above presented arrangement this preferred embodiment can be also designed with both driving means in a stationary arrangement as shown in Fig. 2. The motion screw 1 carrying the nut 2 is on one end co-axially coupled with the output shaft 5 of the first electric motor 3 and on the other end it seats in a first bearing 11. The second electric motor 7 is coupled with the nut 2 by means of a non-slip gear. The output shaft 6 of the second electric motor 7 is co-axially coupled with a guide rod 12 having its free end seated in a second bearing 13. The guide rod 12 engages with a first gear wheel 14, which by means of a second gear wheel 15 links with a third gear wheel 16 The third gear wheel 16 is co-axial and rigidly jointed with the nut 2. The third gear wheel 16 could be replaced by a gearing located directly on the nut 2 periphery. The first gear wheel 14 seats on the guide rod 12 slidably and engages with the guide rod 12 by means of a key 17. which matches with a longitudinal groove 18 in the guide rod 12. The first, second and third gear wheels 14,15,16, including the nut 2, are seated in a frame 19, to which there is fixed the mass element 10.

The operation of this arrangement is the same as described above. With equal rotation speeds ns.nm of the motion screw 1 and the nut 2 the mass element 10 stands still, when these speeds are different the nut 2 moves along the motion screw 1 in one or the other direction and its movement is transferred by the frame 19 upon the mass element 10. In this design the second gear wheel 15 could be omitted, but in such arrangement the output shaft 6 of the second drive means has to rotate contrarywise to the output shaft of the basic drive means This arrangement also complies with the principle of the invention, as it manifests the same sense of rotation of the motion screw 1 and the nut 2 Such solution with both drive means rigidly mounted allows for mounting of the drive means outside a controlled mechanisms, thus providing for transfer of driving force to the powei assembly through appropriate gears The construction also results in an increased operational area and improved design of a machine-tool To improve control features of the power gear assembly according the disclosed invention, it could be further equipped with some options, the solution of which can be seen from Fig 3 The arrangement of driving members, the motion screw 1 and the nut 2. and their engagement with driving means, the electric motors 3.7, and the connection with the supply and control unit 4 is the same as presented in Fig. 2 According to another aspect of the invention this embodiment is furnished with three pairs of non-slip gears The first pair of gears consists of fourth and fifth gear wheels 21,22. the first one seating on the motion screw 1, and further on of a sixth gear wheel 23, which is seated on the guide rod 12 and engages with a seventh gear wheel 24 This seventh gear wheel 24 is through a releaseable first clutch 25 coupled with the fifth gear wheel 22 The first clutch 25 actuator 26 is connected to a first control output 27 of the supply and control unit 4 The output gear ratio n of the first pair of gears equals one. If the first clutch 25 is in an engaged state it provides for exactly the same speed of the motion screw 1 and the nut 2, and thus for standstill of the mass element 10 The second pair of gears is designed similarly An eighth gears wheel 31 is seated on the motion screw 1 and engages with a nineth gear wheel 32 A tenth gear wheel 33 being rigidly jointed with the guide rod 12 engages with an eleventh gear wheel 34 which is through a releaseable second clutch 35 coupled with the nineth gear wheel 32. A second clutch 35 actuator 36 is connected to a second control output 37 of the supply and control unit 4. The output gear ratio i₂ of the second pair of gears exceeds one, preferahly is close to one. And the third pair of non-slip gears shows similar design. A twelveth gear wheel 41, seating on the motion screw 1, engages with a thirteenth gear wheel 42. A fourteenth gear wheel 43, seating on the guide rod 12, engages with a fifteenth gear wheel 44, which is through a releaseable third clutch 45 coupled with the thirteenth gearwheel 42. A third clutch 45 actuator 46 is connected to a third control output 27 of the supply and control unit 4 . The output ratio i₂ value of the third pair of gears is lower than one, preferably close to one. The second and the third clutches 35,455 while in an engaged state provide for a fine finishing feed of the mass element 10 in one. or the other direction respectively. Nevertheless in one moment only one of the clutches can be activated, the other two ones are inoperative and therefore only one pair of gears is in operation. This three. pairs of non-slip gears precisely define the relative movement of the motion screw 1 and the nut 2. These options further decrese a demand upon the supply and control unit 4 and enable to swith off one of the driving electric motors 3,7 during the fine finishing feed or when the mass element 10 is in a standstill.

Another preferred embodiment, presented in Fig. 5, comprises a planetary gearing. The central wheel 101, providing for the first driving member, is directly coupled with the first drive means consisting of a first electric machine 105 and the supply and control unit 4 . An output shaft 111 of the central wheel 101 is directly and co-axially coupled to an output shaft 151 of the first electric machine 105. The crown wheel 102, as the second driving member, is coupled with second drive means, comprising a second electric machine 106 and the same supply and control unit 4 as applies for the first drive means. Here the coupling is pertormed by the first gear wheel 14, having an output shaft 114 directly coupled to a co-axially arranged output shaft 161 of the second electric motor 106. A carrier 103 is couppled with the output, shaft 141 of at least one satellite or a planet gear 104. Usually a planetary gearing includes three or five such planet gears 104, evenly displaced along the periphery of the centraI wheel 102, their output shafts 141 seating on pins of the carrier 103. The carrier 103 is a driven member of the planetary gearing. In this design of the second preferred embodiment, the output shafts 151, 161 of both electric: machines 105, 106 have different sense of rotation. If necessary both output shafts 151,161 of electric machines 105,106 may run with the same sense eif rotation by means of a gearing, which consists of a second gear wheel 15, the output shaft 115 of which is directly coupled with the second electric machine output shaft 161, and further of a third gear wheel 16 having an output, shaft 116 directly coupled with the first gear wheel output, shaft 114. Such an arrangement is presented in both Figs. 6 and 7. In all these cases the supply and control unit 4 comprises independently controlable first and second freguency converters 174. 175 and a control block 173, which applies for both converters. The first freguency converter 174 has an output, representing a first output 171 of the supply and control unit 4, connected to the first electric machine 105 working winding and the second freguency converter 175 has its output, representing a second output 172 of the supply and control unit 4, connected to the second electric machine 106 working winding. The planetary gearing as diclosed in Figs 5, 6, 7, with the central wheel 101 and the crown wheel 102 to be rotated in opposite sense of rotation, works basically as a speed reducer. If is also easily feasible to let the central wheel 101 and the crown wheel 102 rotate in the same sense and thus perform speed multiplication. Nevertheless in both cases it manifests a wide range of freely variable output ratios between a speed of the central wheel 101, as an input speed, and the carrier 103 speed, as an output speed of the planetary gearing, covering speeds from the carrier 103 standstill, occuring at any circumferential speed v_c , v_k of the central wheel 101 and crown wheel 102 when both values are equal, to the theoreticaly highest possibles level, when both the central and the crown wheels 101,102 have the same sense of rotation

The operation of the planetary gearing in the embodiment according the invention can be also described by means of Fig.4, provided the broken curve signed n_k now stands for the central wheel 10l circumferential speed v_c and the broken curve ris here represents the crown wheel 102 circumferential speed VR and what has been above said about, the mass element10 speed applies similarly to the carrier input shaft 131 speed. From Fig. 4 it is also obvious, that, the instant impactless reversing of the carrier output shaft 131 in thr> time point T4 could be easily performed by a sudden raise of the central wheel 101 circumferential speed v_c while simultaneously reducing the crown wheel 102 circumferential speed v_k. It is also obvious, that such an impactless reversal of the carrier 103. having i.e. the sense of rotation resulting from the dominating central wheel 101 circumferential speed v_c , could be easily accomplished by a mere increasing of the crown wheel 102 circumferential speed v_k above the level of of the circumferential speed v_c of the central wheel 101, while keeping that one untouched. Thus the crown wheel 102 circumferential speed v_k now becomes the dominating speed for the new sense of the carrier 103 rotation. This analogically applies for the case when, until the moment ed a reversal, the sense of the carrier 103 rotation is determined by the prevailing crown wheel 102 circumferential speed v_k. Undoubtedly besides these basic procedures of reversals of the mass element 10 motion there exists an unlimited range of variable dynamic levels of such changes of the sense of rotation.

To improve the control of the planetary gearing in the embodiment acording the invention it can be furnished with the same options as described above for the motion screw 1 with the nut 2, as shown in Fig. 7. The fourth, eighth and twelweth gear wheels 21,31,41 seat on the output shaft 151 of the first electric machine 105, while the sixth, tenth and fourteenth gear wheels 23,33,43 are attached on the output shaft 161 of the second electric machine 106. The arrangement of the rest of the gearing including the first, second and third releaseable clutches 25,35,45 corresponds to the assembly presented in Fig. 3 and described with respect to the first preferred embodiment of the invention. Similarly the above disclosed performances and effects of this option apply also for its application with the planetary gearing. Further if also applies that the actuators of all three releaseable clutches 25,35, 45 are connected to the control outputs of the supply and control unit 4 though in Fig.7 these connections are not shown.

From all the above revealed embodiments of the present invention and from all the arangements of the drive means it is obvious that no special driving units are necessary, on the contrary, standard asynchronous sguirrel-cage motors are quite satisfactory. Nevertheless there can be applierl any source of a rotational motion, e.g. a rotational hydraulic motor, for special applications of the gear assembly in guestion even a combustion engine. The expression "output shaft" herein indicates free shalt ends of the applied electric motors 3,7 or electric machines 105,106. In general if stands for an output shaft of drive means, e.g. motors provided with gears, which engage with both the first and the second driving members, i.e. with the the motion screw 1 arid the nut 2, or with the central wheel 101 and the crown wheel 102 respectively. The expression "output shaft" also indicates the output, shaft 131 of the driver 103, the driver 103 being the basic driven member engaging with the mass element 10, which as described above, represents any moving part of a machine-tool, such as a spindle or a motion screw.

Industrial applications

The present invention is designed for a control of linear feeds in machine tools of various types, preferably for reversing feeds. It can be applied for all similar reversing drives especially for reversals of large mass of inertia. or for reversals with high repeat frequency.

Claims

C L A I M S

1. Power gear assembly producing motion of a mass element, preferably a reciprocating movement, the assembly being equipped with at least two mutually rotatably arranged members, the one of which, as a driving member , being coupled with basic drive means generating its rotation with respect to the other members, c h a r a c t e r i z e d i n, t h a t one other member of the assembly as a second driving member, is coupled with independent second drive means for producing a rotation of the said second driving member with respect to the first driving member.

2. Power gear assembly producing motion of a mass element according to claim 1, c h a r a c t e r i z e d i n, t h a t both the first and the second driving members are, each of them individually, engaged with their appropriate drive means through a non-slip gear.

3. Power gear assembly producing motion of a mass element according to claim 1, c h a r a c t e r i z e d i n, t h a t the second drive means comprise an output shaft (6, 161) engaging with an output shaft (5, 151) of the basic drive means through at least one pair of non-slip gears, the gears of the said pair being intercoupled by a releaseable clutch (25, 35, 45).

4. Power gear assembly producing motion of a mass element according to claim 1, c h a r a c t e r i z e d i n, t h a t the first driving member comprises a motion screw (1) and the second driving member comprises a nut (2).

5. Power gear assembly producing motion of a mass element according to claim 1, c h a r a c t e r i z e d i n, t h a t it comprises a planetary gearing having a central wheel (101) as the first driving member and a crown wheel (102) as the second driving member, while a third member, a driver (103) provides for a driven member.

G. Power gear assembly producing motion of a mass element, according to claim 1, c h a r a c f e r i z e d i n, t h a t the nut (2) is engaged with the second drive means through a gearing, the one gear wheel of which is engaged with a guide rod (12), the said guide rod (12) being coupled with an output shaft of the second drive means, provided the said gear wheel is seated on the guide rod (12) slideably.

7. Power gear assembly producing motion of a mass element, according to claim 1. c h a r a c t e r i z e d i n, t h a t the second drive means comprise the same supply and control unit (4) as the basic drive means.

0 Power gear assembly producing motion of a mass element, according to claim 1, c h a r a c t e r i z e d i n, t h a t at least one clutch of the releaseable clutches (25, 35, 45) is connected to the supply and control unit (4).