ACTUATOR

Abstract: A motor (20), a ball screw shaft (12) and so forth are accommodated in a frame (18) constituting an outer frame, and direct-drive guides (23) are provided on both sides of a groove-like opening (22) formed in this frame. The ball screw shaft (12) is provided at the central portion of the frame (18), and a table (16) slides along the direct-drive guides (23) by virtue of rotational action of the ball screw shaft (12). A ball screw spine (26) is provided along the full length of the ball screw shaft (12), which is supported at the ends thereof by means of the motor (20) and the bearing (14), respectively. The rotational centers of the ball screw shaft (12), motor (20) and bearing (14) are aligned with each other by means of balls (32) inserted into the spline (26).

Description: TECHNICAL FIELD The present invention relates to an actuator according to the preamble of claim 1. BACKGROUND ART Slider actuators, as well as other actuators for industrial, medical or public use applications for effecting controls such as linear and rotational movement control, force control, position control, pattern control, phase-plane profile control, non-linear control, compliance control, etc. using rotatable drive sources [such as a rotatable electric motor, a fluid-pressure rotatable motor (using air, hydraulic pressure, water pressure or the like), a fuel engine, a biological-organism principle motor (a flagellum motor)] or the like generally include a coupling or connecting means intended for coupling the drive source to a means for effecting linear or rotational movement. Further, electrical, fluidic, chemical-substance and biochemical drive sources are generally united into a work module in a compact manner, with the actuator bodies or actuators being aggregated together with control drivers used for the drive sources and power sources (such as a generator, a compressor, a vacuum pump, a fuel battery, or a biological energy or chemical energy source). A CIM and FA system, or Virtual Reality/Artificial Reality system is used to attempt to construct a modular distributed/integrated system for the CIM and FA system, with the Virtual Reality/Artificial Reality system being incorporated therein. Further, the individual actuators include control, distribution and intelligent control devices (such as a sequencer having a communicating and radio-communication exchanging means), a power system (e.g., electrical, fluid, fuel, chemical energy substance and biological energy substance sources) and a signal system, all of which are incorporated in an arrangement for the respective modules, a bus system and actuators. In the individual actuators referred to above, however, the coupling between a slider drive source and a drive shaft thereof cannot be easily performed with high accuracy. It is also difficult to make reduce the size of each actuator, since the interconnection between the drive source and the slider drive shaft are performed by coupling. Further, a problem arises in that a distortion occur at each actuator body, depending on the guide structure of the slider. JP-U-63-198 857 discloses an actuator wherein a slider is driven by a motor via a ball-screw shaft. The rotational motion of the motor is converted into a linear motion of the slider which is displaced along the ball-screw shaft. Two separate motors are provided, the first located at the righthand end of the housing and another motor disposed beneath the slide-table. The free end of the shaft is not supported in a bearing so that there is a danger of vibrations implied by the free end of the shaft and influencing the movement of the slider. Further, there is no indication of the length of the threads of the shaft, particularly with regard to the location where the shaft is connected to the rotor of the end motor. Similarly JP-U-63-62 657 does not disclose the length of the ball-screw splines over the feed screw shaft. Nor is disclosed, whether a bearing is provided at the end of the shaft of the motor are how the shaft is disposed within the rotor of a motor or bearing. DISCLOSURE OF THE INVENTION It is an object of the invention to facilitate alignment of the shaft and the rotor of a motor. Therefore, an object of the present invention is to minimize the need for adjustment and maintenance of a coupling means as much as possible. Further, another object of the present invention is to provide an actuator capable of improving the dynamic and static characteristics of a connecting means or the like by reducing the weight, noise, produced dust, and generated heat thereof, and thereby converting rotational motion into translatory motion with high efficiency. In order to achieve the above objects, an actuator according to the present invention comprises the features of claim 1. The present invention is also characterized in that the motor and the feed screw shaft are accommodated within a frame forming an outer frame. The present invention is further characterized in that the frame has a groove-like opening defined therein, and direct-acting guides are provided in the vicinity of the opening. The present invention is still further characterized in that grooves are provided on both sides of each of the direct-acting guides, and guides for guiding the slider are inserted into the grooves respectively. The present invention is still further characterized in that the slider is slidably moved along the guides by rollers interposed therebetween. The present invention is still further characterized by the features as set forth in claims 6 and 7. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an actuator according to a first embodiment of the present invention; FIG. 2 is a partly-cut perspective view illustrating the actuator shown in FIG. 1; FIG. 3 is a partial cross-sectional view showing the actuator shown in FIG. 1; FIG. 4 is a cross-sectional view depicting a motor used for the actuator shown in FIG. 1; FIG. 5 is a cross-sectional view illustrating a bearing of the actuator shown in FIG. 1; FIG. 6 is a perspective view showing another embodiment of an actuator according to the present invention, in which the relationship between a table employed in the embodiment and a body of the actuator is described; FIG. 7 is a perspective view showing a further embodiment of an actuator according to the present invention; FIG. 8 is a partly-cut exploded perspective view illustrating the actuator shown in FIG. 7; and FIG. 9 is a perspective view for describing the shape of a controller employed in a still further embodiment of an actuator according to the present invention. BEST MODE FOR CARRYING OUT THE INVENTION An actuator according to the present invention will hereinafter be described in detail by preferred embodiments with reference to the accompanying drawings. FIG. 1 is a perspective view of an actuator according to a first embodiment. FIG. 2 is a partial perspective view of the actuator shown in FIG. 1. FIG. 3 is a partial vertical sectional view of the actuator shown in FIG. 1. FIG. 4 is a cross-sectional view of a motor used for the actuator shown in FIG. 3. FIG. 5 is a cross-sectional view of a bearing used for the actuator shown in FIG. 1. FIG. 6 is a perspective view of another embodiment in which the relationship between a table and an actuator body is described. The actuator 10 according to the first embodiment is comprised principally of an actuator frame 18 (hereinafter called merely a "frame"), a table 16 movably disposed in the frame 18, a ball screw shaft 12 for driving the table 16, a motor 20 for rotating the ball screw shaft 12, a bearing 14, and a motor controller 24 using, for example, an inverter, of a type wherein programmable controllers (such as input, output, data-input, program-input, display, start, end and stop buttons and an emergency button) are integrally formed therein. As shown in FIG. 2, the actuator 10 is constructed such that the frame 18 thereof forms an outer frame and holds or accommodates the motor 20, the ball screw shaft 12, etc. therein. A pair of direct-acting guides 23 is provided on both sides of a groove-like opening 22 centrally defined in the frame 18. Further, the ball screw shaft 12 is provided at the center of the frame 18, and the table 16 slides along the direct-acting guides 23 due to the rotating action of the ball screw shaft 12. The ball screw shaft 12 has ball-screw splines 26 formed over its entire length and both ends thereof supported by the motor 20 and the bearing 14. Since the coincidence or concentricity between the axis of the ball screw shaft 12 and the axis of each of the ball-screw splines 26 is highly accurate as shown in FIG. 5, no special structural arrangement is required for supporting the ball screw shaft 12 by the bearing 14, or for producing the ball screw shaft 12. The support structure is constructed as follows: Male screws 30 are formed on the outer periphery of the ball-screw splines 26, and stoppers 34 are provided to fix the ball-screw splines 26 and a bearing 36. Since, in this case, the rolling contact surfaces of the ball screws are precisely concentric, they are preferred as standards for the shapes, dimensions and geometrical tolerances of the screws. Needless to say, if the outer diameter of the ball screw shaft 12 is higher in accuracy, then its outer diameter may be set as the standard. When it is desired to fix the bearing 36 to profiles 28 provided between the ball-screw splines 26 using balls 32, the diameter of each ball 32 may suitably be selected to adapt to the accuracy of processing of the two. On the other hand, when the ball screw shaft 12 is fixed to the motor 20, male screws 40 are provided on the outer periphery of the ball-screw splines 26 so as to correspond to a rotor 38 as shown in FIG. 4, and stoppers 42 are attached to the motor 20 in a manner similar to the method for fixing the ball screw shaft 12 to the bearing 14, to thereby fix the ball-screw splines 26 and the rotor 38. In order to cause the rotor 38 to correspond with the stator 44 of the motor 20 at a predetermined position, a bearing 46 is fixedly provided outside of the stoppers 42, in accordance with a method similar to the fixing method of the rotor 38. A driving force of the motor 20 is transmitted to a ball-screw bush 72 (see FIG. 2) through the ball screw shaft 12. Further, the rotational motion of the ball screw shaft 12 is converted into a linear motion to thereby displace the table 16. The first embodiment of the actuator according to the present invention is basically constructed as described above. A structure made up of a combination of a table 16 and a frame 18 will next be described as another embodiment with reference to FIG. 6. Respective pairs of grooves 48, each shaped substantially in the form of a letter T, are provided on both sides of a direct-acting guide 23 disposed on both sides of each of groove-like openings 22 defined in the frame 18. Respective pairs of guides 50, each of which serves as a rail for guiding the table 16, are fitted and inserted into corresponding grooves 48. Each of the guides 50 is shaped substantially in the form of a letter T, so as to be fitted into the groove 48. Further, V-shaped grooves are respectively defined in portions of the guides 50, which guide the table 16. Longitudinally-extending rubber contacts 54, each of which is used to supply power to the table 16 from power lines 52 provided within the frame 18, are provided inside one of the groove-like openings 22. The rubber contacts 54 are conductively connected with corresponding contacts 56 attached to the table 16 through either brushes or electricity-conductive cam followers, so as to effect the supply of power to the contacts 56 of the table 16. Further, either a light-emitting/light-receiving diode 58 or other communication device for transmitting signals to and receiving signals from the table 16 is provided inside the other of the groove-like openings 22. Either a photodiode 60 or other communication device for effecting optical communications, microwave communications and spread spectrum communications (which are excellent in resistance to noise in particular) over either the light-emitting/light-receiving diode 58 or the other communication device is attached to the table 16. A pneumatic path space may be used as a communication path for such communications. The power supplied to the contacts 56 of the table 16 is supplied thereto by a connector 64 provided on the upper surface of the table 16. The connector 64 may be any standardized connector such as a DIN connector. The angle of the connector may be varied through an angle of 90°. Further, the photodiode 60 is electrically connected to the connector 64 and a connector 65. The turning angle of the ball screw shaft 12 is detected by an encoder 66 attached to one end of the ball screw shaft 12 (see FIG. 2). The encoder 66 may preferably comprise either an absolute type encoder or an absolute-signal output type integral encoder using an integrating counter memory. The encoder 66 has a sensor signal processing circuit, a serial signal generating circuit, etc. all of which are not shown. A controller 68 disposed adjacent to the motor 20 comprises a driver module, a control module and a communication interface (not shown), depending on the function of the controller. The electrical connection between the communication interface and an unillustrated external device is made by connectors 70a and 70b. The driver module has a driver for driving the motor 20, and a driver controller for controlling the drivers on an integral or united basis. Incidentally, the driver is used to effect a PWM and a digitally-controlled inverter control. The control module controls or manages an actuator operation program, and transmits a position command or instruction and a speed instruction, or other drive control instructions, to the driver module. Further, the control module monitors signals fed back from the motor 20 and respective components of the driver module. The communication interface provides mutual communications between a communication system and the control module via a serial or parallel interface. The communication system can be a LAN or an external controller, a PC (Programmable Controller/Personal Computer), a PLC (Programmable Logic Controller), or other types of computers, an Ethernet, a token ring, a MAP, a PC, a LAN, a LON (Local Operating Network), a WAN, an OSI, etc. The serial interface may comprise a RS232C and a RS422, or an interface dedicated to a GP-IB, a BCD and a Centronics parallel LAN. The parallel interface may comprise a highspeed optical LAN of 100-Mbps or the like, a Gateway, etc. The entire software structure is analyzed and constructed by an object oriented system or by programming. Further, each of the software, data, logic, or hardware structures is set as a recursive structure. The respective components of each controller 68 may be integrally formed to realize a reduction in size. Alternatively, the components may be so constructed that they can be separated into various functions and held in common to many kinds of actuators, in order to improve general-purpose properties and realize a reduction in cost. For example, the control functions of the control module may be fully digitalized or semi-digitalized using an ASIC, a one-chip multi CPU, a DSP or the like, so as to realize both high function and low cost. Further, a complex control using a counterbalance set on a pneumatic actuator and a belt pulley, a cylinder air balance set on a belt pulley, a double-velocity air balancer, a multiaxis control using an endeffect, a force control, a position/velocity control, an XYZ, a  coordinate, etc., and a device control using a conveyor, a turntable, an index table, a lifter, etc. can be performed simultaneously or integrally, along with simultaneous or integral control of various induction motors, an AC servomotor, a DC servomotor and a stepping motor, by switching a predetermined software in advance or in the course of operation as needed, thereby making it possible to further improve function and reduce cost. If the above-described system configuration is established, a self-decentralizing system can be achieved by using a CIM/FA intelligent system. If a decision is made on motors to be controlled and corresponding interface formats based on impedances, circuit configurations or the like, and an identification memory using a data carrier, bar codes, ID tags or the like to thereby automatically cope with such a process via software, it is then possible to eliminate or greatly reduce labor cost and provide intelligent functions by constructing either a network or a line. Further, signals may be simultaneously transmitted using a power supply line connected to a motor or the like, to eliminate extraneous conductors or wires. An active noise control may be performed as a noise countermeasure for the actuator. In addition, attitude and rotational controls may be carried out by a triangular-pole type piezo-resonant (three dimensional) gyroscope. A casing for the encoder 66 and the controller 68 is used in common with the frame 18. However, the casing and the frame 18 may be separate from each other depending on the construction of the actuator. In this case, the casing is fitted on the frame 18 by circular or polygonal fittings, or by engagements, pins or the like. Further, the transfer of electricity and signals, and the couplings between a bus, a LAN and a sensor or the like are also performed by connectors. In addition, fitting and connections between the two are effected simultaneously, and they are fixed together by caulking or welding using electron beams or the like. Alternatively, the controller, the motor, etc. may be shaped respectively in the form of modules, and may be added or removed as needed. A further embodiment of an actuator employed in an arrangement will now be shown in FIGS. 7 and 8. This type of actuator is substantially identical to the actuator shown in FIG. 1. Therefore, the same structural elements as those in the actuator shown in FIG. 1 are identified by like reference numerals, and will not be described in detail. However, the present actuator differs in structure from the actuator shown in FIG. 1 in that a table is accommodated within an actuator frame, and direct-acting guides are also provided within the actuator frame. Further, the controller 68 shown in FIG. 2 may be constructed as a combination of respective functions, comprising a display section 200, an operation section 202, a data and program input section 204, a start and emergency stop button 206, an external communication control interface, a LAN interface 203, a power input section 205, etc. as shown in FIG. 9. Thereby, such elements can be positionally changed from a horizontal to a vertical direction or vice versa, or from an upward to a downward direction or vice versa, or from left to right or vice versa, and they can be positionally shifted or rotated to expose other surfaces thereof. The controller shown in FIG. 18 is shaped in the form of a cube, but may be shaped in the form of either a hexagon or an octagon. Further, the controller may be disposed between a plurality of adjacent actuators so as to control the actuators. Moreover, a power source used for the controller may be electrically series-connected to the controller. INDUSTRIAL APPLICABILITY According to the present invention, as has been described above, a rotating source can be easily and accurately made concentric with a rotatable shaft, by integrally aligning a feed screw shaft serving as a rotational and linear motion converting means with both the rotating source and the rotatable shaft. An actuator can be reduced in size by forming pulley gears for a timing belt and a V belt integrally with the rotor of a motorized drive source. Even when the direction of rotation is changed by means of helical gears, such helical gears can be formed integrally with a rotor of a rotatable drive source so as to eliminate coupling and provide a reduction in size. Further, an arrangement for actuators, supporting actuators, or both can be formed integrally with a casing for a drive source, so as to provide a further compact configuration. Thus, a rotational and linear bearing means for a drive source, a transmission gear and a slider can be reduced in number and enhanced in rigidity. The arrangement, the drive source, the transmission gear and the slider can also be made compact by precision investment casting, metal pressing, extrusion, drawing or injection molding.

Claims: An actuator comprising: a feed screw shaft (12) operatively connected at one end thereof to a rotor (38) of a motor (20) for converting a rotational motion of said motor (20) into a linear motion to displace a slider (16), characterized in that said feed screw shaft (12) is connected at an opposite end thereof to a bearing (36, 14) permitting rotational motion of said feed screw shaft (12), and that said feed screw shaft (12) has ball-screw splines (26) formed over its entire length, wherein said feed screw shaft (12) is connected with said rotor (38) and said bearing (36, 14) such that a center of rotation of said feed screw shaft (12) is aligned with a center of rotation of said rotor (38) and a center of rotation of said bearing (36, 14) by a plurality of balls or strings (32) disposed in said ball-screw splines (26) between said feed screw shaft (12) and said rotor (38), and between said feed screw shaft (12) and said bearing, respectively. An actuator as claimed in claim 1, wherein said motor (20) and said feed screw shaft (12) are accommodated within a frame (18) forming an outer frame. An actuator as claimed in claim 2, wherein said frame (18) has a groove-like opening (22) defined therein and direct-acting guides (23) are provided in the vicinity of said opening (22). An actuator as claimed in claim 3, wherein grooves (48) are provided on both sides of each of said direct-acting guides (23), and guides (50) for guiding the slider (16) are inserted into said grooves (48) respectively. An actuator as claimed in claim 4, wherein said slider (16) is slidably moved along said guides (50) by rollers interposed therebetween. An actuator as claimed in claim 1, wherein said ball-screw splines (26) further comprise male threads (30) provided on a periphery thereof. An actuator as claimed in claim 6, further comprising stoppers (34, 42) threadedly engaged with said male threads (30) of said ball-screw splines (26) for securing said ball-screw shaft (12) to said rotor (38) at said one end, and for securing said ball-screw shaft (12) to said bearing (36, 14) at said opposite end thereof, respectively.

Inventors: NAGAI SHIGEKAZU SMC, SAITOH AKIO SMC, SUGIYAMA TORU SMC, NAGAI, SHIGEKAZU, SAITOH, AKIOR, SUGIYAMA, TORU, SMC, NAGAI, SHIGEKAZU, SMC KK, TSUKUBA GIJUTSU CENTER, SAITOH, AKIO, SMC KK, TSUKUBA GIJUTSUCENTER, SUGIYAMA, TORU, SMC KK, TSUKUBA GIJUTSU CENTER
Applicants: SMC KK, SMC KABUSHIKI KAISHA
Application year: 1992
Main classification: F16H25
IPC codes: B23Q1, A61B17, F16H25, H02K7