GB1598656A

GB1598656A - Servo-controlled rotary actuators

Info

Publication number: GB1598656A
Application number: GB13539/78A
Authority: GB
Original assignee: Basfer SRL
Current assignee: Basfer SRL
Priority date: 1978-03-31
Filing date: 1978-04-06
Publication date: 1981-09-23
Also published as: FR2421414A1; FR2421414B1; DE2815298A1

Description

(54) IMPROVEMENTS IN SERVO-CONTROLLED ROTARY ACTUATORS (71) We, BASFER S.R.L., an Italian Company of Viale Sarca, 2 Milano, Italy, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement::- This invention relates to improvements in servo-controlled rotary actuators, and, more particularly, to a machine with closed circuit means of regulation, comprising at least one pair of arms connected by an articulated joint and a rotary fluid-pressure operated actuator for the displacement of one arm with respect to the other, the said actuator comprising an external annular part integral with one of the said arms, an internal part coaxial and concentric to the said external part, and integral with the other arm, variable volume cavities between the said external and the said internal parts forming internal thrust and counter-thrust surfaces, conduits communicating with said cavities, and a valve connected to said conduits in order to control the relative angular displacement of the said external and the said internal parts in one of two opposite directions.

In such machines that is to say, machines formed out of two or more articulated arms such as, for example, what are called "robot" machines with closed circuit regulation for painting, the movements thereof are transmitted via actuators mounted in the region of the articulations.

With closed circuit servosystems (that is to say, where a feedback originating at the system outlet is carried back to the inlet) it is necessary to reduce as much as possible resonance phenomena, which have a considerable adverse effect on the operating movements determined by the aforementioned actuators. The lower the resonant frequency of the system, and the greater the play between the moving parts of the structure, the greater are said resonance phenomena.

For certain jobs, such as painting, there is also the need for the actuators not to suffer damage, or to be put out of use, as a result of the inevitable mist of paint that is suspended in the air in the working area.

At the present time, automatic machines with rotary hydraulic actuators have shown themselves to be fairly satisfactory since the said actuators are free of excessive play and their internal parts are well protected against the mist of paint or other agents present in the working area. On such known machines, the hydraulic actuators are mounted laterally on the articulations, and in their internal part they comprise a shaft, the diameter of which is calculated to suit the torque to be transmitted for the relative angular displacement of the arms.

The shaft of each hydraulic actuator is connected to the pin that constitutes the fulcrum point of the relative articulation, which is normally of a far greater diameter than that of the said shaft. The connection between the shaft of the actuator and the pin of the articulation, in turn integral with one of the arms of the pair concerned, is achieved through a joint able to compensate for error in axial alignment.

The said automatic machines of known type, equipped with hydraulic actuators, are subjected, however, to operational irregularity due to the frequent presence of troublesome resonance phenomena.

Furthermore, to fit a joint between each actuator and the articulation operated by the said actuator has proved to be onerous and cumbersome.

According to the present invention there is provided a machine with closed circuit means of regulation, comprising at least one pair of arms connected by an articulated joint, and a rotary fluid pressure operated actuator for the displacement of one arm with respect to the other, the said actuator comprising: an external annular part integral with one of the said arms, an internal part coaxial and concentric to said external part and integral with the other arm, an internal sector-shaped projection integral with said external part and an external sector-shaped projection integral with said internal part, which projections form internal thrust and counter-thrust surfaces and define, with said internal and external parts, two variable volume cavities, two conduits communicating with said cavities, and a valve for selectively connecting said conduits to a source of pressurized fluid or to discharge in order to control the relative angular displacement of said projections of said internal and external parts in one of two opposite directions, wherein said internal part integral with one of said arms constitutes a fulcrum on which is pivotally mounted, for relative angular displacement, said external part integral with the other arm, the said external and internal parts together constituting said articulated joint and the mean application radius of thrust against said internal thrust and counter-thrust surfaces being more than twice the radial dimensions of said surfaces, so as to produce high resonant frequencies.

Preferably said two conduits are formed in said internal part and have terminal radial sections respectively on one side and on the other side of said sector-shaped projection integral with the internal part adjacent the thrust and counter-thrust surfaces, said terminal radial sections being selectively partially closable by said sector shaped projection integral with the external part adjacent a respective end position thereof in order to damp relative movement of said internal and external parts immediately before reaching said end position.

The advantages the invention offers lie in the direct use of the internal part of the actuator as the fulcrum for the articulation, thereby rendering lateral connecting joints unnecessary and notably decreasing resonance phenomena in the resulting system.

One preferred embodiment of the invention is illustrated by way of example, in the accompanying drawings, in which: Fig. 1 is a diagrammatic perspective view of an apparatus with two arms, in which the inventive idea described herein is incorporated; Fig. 2 is a diagrammatic axial section of the articulation of the apparatus illustrated in Fig. 1; Fig. 3 is a cross section of the articulation of the apparatus illustrated in Fig. 2; Fig. 4 is a cross section similar to that shown in Fig. 3 but with the arms in a different angular position.

With reference to the aforementioned Figures, at 1 and 2 two arms are shown, these being joined one to the other by means of an articulated joint and forming part of a machine. The said machine can be of the type depicted in Fig. 1, utilized for painting, for example, through the mounting of a spray gun onto a support member 30 fixed to the free end of the arm 1. The said type of machine comprises a base 4 in which a hydraulic control unit (not shown on the drawings) is housed.

The said automatic machine can have any desired number of arms.

The rotating hydraulic actuator, generally indicated at 5 in Fig. 2, comprises an external annular part 6 and an internal cylindrical part 7 constituting, as will be seen better in due course, the fulcrum point for the articulation onto which the said actuator is mounted. The external part 6 is rendered integral with the arm 1 and it is concentric and coaxial to the internal part 7, which is rendered integral with a terminal fork 2a (Fig. 2) of the arm 2. The annular part 6 has internally a cylindrical ring shaped groove 8 (Fig. 2) which is provided with an internal sector shaped projection 9 (Figs. 3 and 4) destined to slidingly grip the internal cylindrical part 7. The latter mentioned part has an external sector shaped projection 10 destined to engage with the internal surface of the said groove 8 in a way whereby it can slide therein.Two annular sector chambers of variable volume, 11 and 12, respectively, are thus defined between the parts 6 and 7, while the said projections 9 and 10 form the relevant thrust and counter-thrust surfaces, 9a-9b and 10a-10b, respectively. To carry operating fluid, preferably oil, into the aforementioned variable volume chambers 11 and 12, the internal part 7 of the actuator is provided with pipes 13 and 14 which are arranged axially and terminate in radial sections 13a and 14a which run into the chambers 11 and 12, respectively. For reasons of clarity, the internal pipe 14 is shown in Fig. 2 displaced angularly through approximately 1800 with respect to the true position depicted in Fig. 3.

The said internal pipes 13 and 14 terminate laterally at a servovalve 15 connected to two pipes, 16 and 17, respectively, through which the operating fluid arriving from the source of the compressed fluid passes. The said servovalve 15 is designed to alternately connect the chambers 11 and 12 to the source of the compressed fluid or to the discharge thereof in known manner.

When compressed fluid is sent, for example, to the annular sector chamber 12, thrust, as shown by the arrows A, is exerted onto the surfaces 9b and lOb. The mean application radius of the thrust forces, marked 18 in Fig. 3 and 4, is more than twice the radial dimension R of the aforementioned surfaces 9b and lOb, and thus sufficient torque is created to angularly displace the arms 1 and 2, one with respect to the other.

It should be noted that a ratio exists between the said mean radius 18 and the resonant frequency of a system that operates with technology using closed circuit means of regulation wherein the most vulnerable point found is in the operating fluid. The said ratio is apparent from the following formula in respect of the resonance pulse w:

in which y=the modulus of elasticity of the operating fluid; j=the moment of inertia applied to the arms; Rrn=the mean application radius of the forces acting on the thrust surfaces; S=the area of the thrust surfaces: C=the travel of the projection 9 with respect to the projection 10 Since the resonant frequency is:: f= 27r it can be said that the said resonant frequency is a function of the mean radius Rm whilst it is a linear function of the square root of the other parameters that appear in the formulae given above.

From the foregoing considerations, the fact emerges that the larger the diametrical dimension of the actuator, the greater the resonant frequency, and thus all the more attenuated are phenomena occurring at low resonant frequency.

The use of large diameters in the construction of the actuators makes it possible for them to be mounted directly on the articulations and for them to be contained within the axial dimensions of the said articulations, as shown in Fig. 2. In this way there is no need for the joint required for the conventional mounting of the actuators onto the articulations (as stated, with known types, the actuator is mounted at the side of the articulation and is connected thereto by-means of a suitable joint).

Moreover, the increased diametrical dimensions suggested by the above mentioned theoretical considerations allow the actuator to form the articulation.

From the foregoing, the operation of the automatic machine according to the invention can clearly be seen.

When the servovalve 15 is operated to send fluid under pressure to, for example, the chamber 12, while the chamber 11 is connected to the discharge, the thrust of the said fluid, acting as shown with the arrows A in Fig. 3, determines the angular displacement of the arm 1 with respect to the arm 2, in a clockwise direction. Thus, a new position, as shown in Fig. 4, is reached wherein the projection 9 has approached the projection 10, progressively closing the radial section 14a of the pipe 14 so creating an efficient damping effect in the final part of the displacement travel.

The high resonant frequency, determined by the fact that the actuator is provided with large diametrical dimensions, reduces to a minimum phenomena occurring at the low resonant frequencies of the operating system.

WHAT WE CLAIM IS: 1. A machine with closed circuit means of regulation, comprising at least one pair of arms connected by an articulated joint, and a rotary fluid pressure operated actuator for the displacement of one arm with respect to the other, the said actuator comprising: an external annular part integral with one of the said arms, an internal part coaxial and concentric to said external part and integral with the other arm, an internal sectorshaped projection integral with said external part and an external sector-shaped projection integral with said internal part, which projections form internal thrust and counter-thrust surfaces and define, with said internal and external parts two variable volume cavities, two conduits communicating with said cavities, and a valve for selectively connecting said conduits to a source of pressurized fluid or to discharge in order to control the relative angular displacement of said projections of said internal and external parts in one of two opposite directions, wherein said internal part integral with one of said arms constitutes a fulcrum on which is pivotally mounted, for relative angular displacement, said external part integral with the other arm, the said external and internal parts together constituting said articulated joint and the mean application radius of thrust against said internal thrust and counterthrust surfaces being more than twice the radial dimensions of said surfaces so as to produce high resonant frequencies.

2. A machine as claimed in claim 1, wherein said two conduits are formed in said internal part and have terminal radial sections respectively on one side and on the other side of said sector-shaped projection integral with the internal part adjacent the thrust and counter-thrust surfaces, said terminal radial sections being selectively

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. displace the arms 1 and 2, one with respect to the other. It should be noted that a ratio exists between the said mean radius 18 and the resonant frequency of a system that operates with technology using closed circuit means of regulation wherein the most vulnerable point found is in the operating fluid. The said ratio is apparent from the following formula in respect of the resonance pulse w: in which y=the modulus of elasticity of the operating fluid; j=the moment of inertia applied to the arms; Rrn=the mean application radius of the forces acting on the thrust surfaces; S=the area of the thrust surfaces: C=the travel of the projection 9 with respect to the projection 10 Since the resonant frequency is:: f= 27r it can be said that the said resonant frequency is a function of the mean radius Rm whilst it is a linear function of the square root of the other parameters that appear in the formulae given above. From the foregoing considerations, the fact emerges that the larger the diametrical dimension of the actuator, the greater the resonant frequency, and thus all the more attenuated are phenomena occurring at low resonant frequency. The use of large diameters in the construction of the actuators makes it possible for them to be mounted directly on the articulations and for them to be contained within the axial dimensions of the said articulations, as shown in Fig. 2. In this way there is no need for the joint required for the conventional mounting of the actuators onto the articulations (as stated, with known types, the actuator is mounted at the side of the articulation and is connected thereto by-means of a suitable joint). Moreover, the increased diametrical dimensions suggested by the above mentioned theoretical considerations allow the actuator to form the articulation. From the foregoing, the operation of the automatic machine according to the invention can clearly be seen. When the servovalve 15 is operated to send fluid under pressure to, for example, the chamber 12, while the chamber 11 is connected to the discharge, the thrust of the said fluid, acting as shown with the arrows A in Fig. 3, determines the angular displacement of the arm 1 with respect to the arm 2, in a clockwise direction. Thus, a new position, as shown in Fig. 4, is reached wherein the projection 9 has approached the projection 10, progressively closing the radial section 14a of the pipe 14 so creating an efficient damping effect in the final part of the displacement travel. The high resonant frequency, determined by the fact that the actuator is provided with large diametrical dimensions, reduces to a minimum phenomena occurring at the low resonant frequencies of the operating system. WHAT WE CLAIM IS:

1. A machine with closed circuit means of regulation, comprising at least one pair of arms connected by an articulated joint, and a rotary fluid pressure operated actuator for the displacement of one arm with respect to the other, the said actuator comprising: an external annular part integral with one of the said arms, an internal part coaxial and concentric to said external part and integral with the other arm, an internal sectorshaped projection integral with said external part and an external sector-shaped projection integral with said internal part, which projections form internal thrust and counter-thrust surfaces and define, with said internal and external parts two variable volume cavities, two conduits communicating with said cavities, and a valve for selectively connecting said conduits to a source of pressurized fluid or to discharge in order to control the relative angular displacement of said projections of said internal and external parts in one of two opposite directions, wherein said internal part integral with one of said arms constitutes a fulcrum on which is pivotally mounted, for relative angular displacement, said external part integral with the other arm, the said external and internal parts together constituting said articulated joint and the mean application radius of thrust against said internal thrust and counterthrust surfaces being more than twice the radial dimensions of said surfaces so as to produce high resonant frequencies.

partially closable by said sector-shaped projection integral with the external part adjacent a respective end position thereof in order to damp relative movement of the said internal and external parts immediately before reaching said end position.

3. A machine with closed circuit means of regulation substantially as hereinbefore described with reference to the accompanying drawings.