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A New Modular Robot System
A New Modular Robot System G. Pritschow - Sponsored by K. Tuffentsarnrner
The idea o f using an industrial robot is to have a flexible machine. adaptable to new tasks It any time without great efforts. But up to now this is only possible with a lot of restrictions. By using both speed-controlled AC drives and hydraulic motors in connection with a state base control the mechanical and the eiectrical components can be put together in a way that the drive is integrated into the robot arm with a minimum of meChdniCa1 parts. By means of special adapters the user is capable t o assemble the robot with the joints and arms on his own. With these components one obtains task-specified robots with free choice In kinematics, torque, Stiffness and path velocity.
lnstitut fur Steuerungstechnik der Werkzeugmaschinen und Fertigungseinrichtungen der Unlversitat Stuttgart, Seidenstrasse 36. 0-7000 Stuttgart 1 1
Device-specific problems in using industrial robots
Industrial robots have found their first use in manufacturing technology in the area of handllng workpieces. where they still are applied to a great extent up to now. In connection with handling always a universal availability was considered t o be most important. In regard to the field of tasks this availability can be fulfilled in a relatively slnple way. although also here one has to take into account that there is only one optimal device construction for one distlnct workp i e c e 3 e c t r e and one task. The most i m p o r t x criteria for the selection of an i n G t r i a l robot for handling are the load and the working range in connection wlth the kinematic structure. For the estimation of robots handling tools or workpieces for manufacturing, criteria are used which among other things are of importance also for the design of machine tools. The process and the requirements to the result of tooling detennine the characteristics of the device. The selection of a robot is made accordlng to the requirements of the procedure a s is shown in Figure 1. Only in very few cases the result is an optimal device, but m c h more a canprmlse of working range. speed, load and rigidity. Frequently, however, overdlrnensioned devices are chosen in order to cover all requirements. Especially when industrial robots are to be used as tooling machines for
Motors, mechanical transfer elernents, links and joints of industrial robots - except the flrst basls axis - belong t o the moving mechanical parts, i. e . the masses of these elements decisively influence the acceleration of the individual axes. The claim for as small masses as posslble can be deduced from this. Nevertheless the structure o f the industrlal robots has to be maintenance-friendly. This can be achieved by the modularization of the construction elements. Especially when us ng y rau Ic drives for industrial robots a corn act construttionh Ps Lquired. This refers essentially to ding mechanism for the hydraulic fluid to the wrists.
6
What results from the claim mentioned above is the requirement to make power density of the drives as high as posslble. The pover spectre o f exlsting drives today includes the range of 100 U (e. g. wrists) up to 10 kW (e. 9. basis axes). The maximum speed of the axes can amount up to ln/s respectively 360. Is for rotational movements. As a rule thls speed 1s to be arrived within a few tenths of a second. lhe angles of rotation for basls axes usually are below 360.. For contlnous path controlled industrial m b o t s often posltioning accuracies of 1/0.05 nn~are required. The speed range ( = ratio of maxirnum to minimum speed) has to be between 100 : 1 for simple handling tasks and 2000 : 1 e. g. for measuring and tooling with the same robot. Besides these requlrements the drives should fulfill the conditions for explosion protection and need as 1Ittle maintenance as possible. 2.2
Drive elements for a modular concept
The drive units of an industrial m b o t hold the biggest share in the costs for the equipment. Therefore they form the main point within the concept for a modular system regarding their modularity and reutilization. At present industrial robots are usually equipped with DC servo drives. Besides high dynamics they have the advantage of
elechohydroulic drim
Figure 1: Applications engineering of robots - grinding. - burrlng. - path welding - coating and varnishing.
d)
there are often difficulties in finding optimally approprlate devices on the market. For the solution o f thls problems special-purpose robots were constructed or existing devices were improved by expensive reconstructions in order to achieve an optimally working robot and its economic use. But further applications In the future will be only cost-effective, if using an appropriate modular robot system, by means of which the user can determine and compose his task-specific robot On his own. 2
Orlves for industrial robots
2.1
Requirements
a,L
rofmy
The drives are subsystems of rentiates between drives for Basis axes mainly serve for Cartesian coordinate system; of the tool.
an industrfal robot. One dlffebasis axes, joints and wrists. reaching polnts described in a wrists serve for the orientation
Annals of the ClRP Vol. 35/1/1986
Figure 2: Drive elements o f a nodular robot system
89
small pulsations in their torque. The speed control is very simply to realize. Disadvantages are the high costs for OC drives, the wear of the comnutator dnd especially the Iimitation of peak torques and speeds by the commutator, which often lead to overdimensioned drives in industrial robots. Due to the progress in the power control and the control of asynchronous and synchronous drives today cost-effectlve drives can be constructed, whose static and dynamic behaviour outperforms that of DC-drlves. Because there is no commutator. they are maintenance-free and possess d high overload capacity. An At motor 1st applied a s drive unit for the modular concept presented. It has a low price, dnd the speed control. whose realization is often considered t o be very expensive. has found a cost-effective solution by using micro computers 121. A l s o the further development of hydraulic drive units and their improvement in their static and dynamic behaviour by state base controls I31 lead t o drive units applicable for a modular system (Figure 2).
3
Elements for modular industrial robots
3.1
Module for linear movements
I n this concept the principle of the
generation of movements is inverted (Figure 2a and 3). The stator of the asynchronous motor is integrated into the supporting slide. The ball screw as a part of tne module is fixed at the engitv foundation. The rotor of the AC motor and the nut are put together as one unit. A digital masurerent equipment for velocity and position feedback is integrated 171. lhe module consisting of ball screw, supporting slide, slideway arid AC motor has the following advantages: - less bearing and no coupling between ball screw and the motor and therefore a high stiffness of the system; - optimal dynamic behaviour as there Is no angular immentum of the ball screw and no critical Speed; - no gear to reduce the angular momentum - increased rigidity of the ball screw because of preloading without problems; - less space required. those of
I
mis 01 symmetry
Figure 4: Drafts of different joint drives In the construction of the joint drive parts of the gear mechanism are parts of the motor at the same time. For thls the stator of the motor is connected wlth one part of the llnk. the other part is connected t o the rotor v i a gears attached on both sides (Figure 5a).
Figure 3: Slide unit of the test drive (seen from below)
A comparison of important data with drive shows the advantages:
b)
0)
Figure 5: a) Joint drive with AC motor and symmetric planet gear b) Prototype The usual couplings between motor and drive are not needed. The measurlng system as a simple pulse generator, which Is also used as a measuring system for the speed, is put on the rotor of the A t motor. In o r d e r to adapt torque and speed planet gears, e. 9. compact drive kits without free motion, type harmonic drive, for wrlsts or eccentric gears for swinging movements are applied. 3.3
Module for rotational and swinging movements
The industrial robot as an open kinematic chain in its most usual kinematics consists of a canbination of rotational and swinging movements. The drive nodule, presented in 3.2, thus is not sufficient for a modular system. Therefore the aim was the realisation of the rotating movement by means of a compact drive in consequent development.
a conventional TW'eh:cI
wrkspcce
31 1
IWC
ljres
votion
conventional drlve with drives integrated nut diameter of ball screw in mn lead of ball screw in mn length o f ball screw in mn mass of slide unit in kg smallest rigidity between motor and tooling point in N/pm realizable velocity gain Kv first mechanical characteristic frequency in Hz 3.2
40
...
50 10
2000 400
25 5 2000 400
15 ... 35 36 ... 66 55 sec-' 100 sec-l
25
... 40
& 40
Module for joint drive
Up to now it is characteristic of jolnts that motor, gear and the measurement equipment for velocity and position feedback are installed seperately on the links (Figure 4). The use of an asynchronous m t o r s allows the installation of motor and gear into the joints of an industrial robot (Figure 5b) in order to create a compact symnetrlcal drive unit of the joint 141. Both this join1 constructions with their relatively high space required and the drive system according to Flgure 4c do not allow an appropriate modular design. This is also the case f o r drive concepts, in which the force is transmitted with hollow shafts, toothed belts ptc.
o=b
1-1
I/-
Figure 6: Approach of the optimal workspace by sqlrared gear configuration
The combinations of the rotating and shinging movements can be shown by a vector 7, which is linked to the point 0 and is revolved round%, andoc,(Figure 6. abcve). The top of the vector here moves on 2 spherical surface. P drive system for these two m o v e w n t s requires a minimum of space. if all its lie within tbis Sphere (theoretically degenerated e:ement t o a point !. With q u a ! requirements to Dcth dies, the minimum space required i s best approximated by a configuration of inside iFigurF 6. differential gears with the motors si!ua!ed below). FFW the symmetrical configuration of t h e motor and the geirr i n the ]Gint advantages result dhich are i i i I i 5 ! also for the fcint drive in 3.2 (Figure 7 ) .
I
.. --__--
II
Figure 9: Modular industiisl robot with three drive units
.
LZZYNW
T7+ **" n&
pJd~dlm#fmt
.\
\
sro*mOrnl
Figure 7 Opsign of a realized j o i n t W:ve
o m b r mde
The integration of tho rnotnrs r h e m s e l w s effects an i n r r e i s e of the mais of the joint. but only in the range of about 1G %. Figure 8 shows a drivp scdule f o r a wrist. Some data verify
the C@mpdCt s?ructure o f thP wrist ma52 included odzpter Jnit diameter o f an enveiopc sphere rated torque f o r rotat\ng or s w i nqi rig movements 2ngular delocity for Mnrrax
:Z kg about i 7 0 mn
F
i
MHrar 0
-
= 60 Nm 9Co/iec
Far the combinpd movement rotating and swinging there I F a separation of t h e power. The drive modules c r e ecuipped with adapters (Figure 8b), whose structure allows to connect the modules and links very quickly with reproducih!e accuracy v i a a s ~ e c i a lclamping d ~ v i c e . In c a r p of need the power s i m p l y i n g lines ml the medns o f process can be guided thrcjuqh tne rnodule.
\
Figure 10: Example of mlulf applica' Module for loint drives on the basis of electrohydraulic 3.4
!notars
In grder to be competitive with the electrical drives mentioned above. modular electrohydraulic drlves In industrial robots must possess a comparable static and dynamic behaviour with ecjual modularlty, lower price and smaller construction vnlume. Esbecially fur firidncial redsons and from points uf vile o f optimal energy utilization therefore only direct drives without further mechanical transfer elements, e. g. gears, cnme intc question. With the restriction to drives with a 1 1 mited regulating range these are:
- tne linear hydraulic actuator fnr the realization of linear movements,
- the blade type motor for the realization of swinging movements.
In d similar way as the joint drive described in 3.2 a drive unit with blade type mator is appropriate as modular a component. Blade type motors have a relatively small rlgldity as is the case in linear hydraulic actuators. Certainly this is a disadvantage and a problem of these motors. These problems can be solved. however. by means of intelligent and effective control systems. Figure 1 1 shows the structure of a discrete state base control for a linear hydraulic actuator, which can be used in the same way for controlling a blade type motor. a)
b)
Figure 8: Actuator module as a wrist a) wrist b) adapter How to compose a complete robot with 6 degrees of freedcm with three drive modules is shown in Figure 9 151. I t makes clear that also kinematically overdimensioned systems, mainly f o r the extension of the working range and adaption, can be rnalized without DrObleInS.
Figure 10 shows how to use the module for the combinations o f the movements 'translation' and 'swinging'. For this the rotating axis is connected with a steering rack via a pinion. A s mechanical transfer element for the linear movement belts or ba!l screws can ! ~ nused, too.
toothed
For the reduction of the nwasuring expenditure state base observers are used. Linear state base controls enable a high ve!OCity gain (Kv) in the range of 100 11s f o r a linearized dorking range o f the non-linear controlled system. The high parameter sensitivity of state base controls with high gain o f the control loop, however, requires the adaption of the control and observer parameters. in order to achieve a good control behaviour in the complete working range of the drive. The control structure shown in Figure 11 and realized on the basis of d micro computer effected a velocity gain at a servo hydraulic drive which was 5 times higher than controlled with a ronventional P-algorithm 131. The necessity and the possibilities of a control realized digitally - on the basis of a computer - becane evident in this mamole. Today it is indispensable for controlling robot drives, because in addition one has to take into account mechanlcal feedbacks due to elastic couplings of further drive units as well as the m n t of inertia which changes with the position o f robot.
91
also of the robst control, in arder to adapt the COntrClS to the possible configurations simoly by t h e inlut Cif *.he r3bTt kinematics v i a parameters. ~iterature /I/
I
'lil>I'
1 1 II
Figure 1 1 : Structure of an adaptive state base control for electrohydraulic drives I31 In order to achieve a compact construction of the joint drive, the blade type motor. the bearing parts of the joint, the v a l ve and the elements for power supply have to be arranged i n a way that saves costs and weight. The prototype of such a drive is presented in Figure 12 161.
WlJPSt.
U.-H.
Dberfltichenschleifen mit HiIfe d c l n Industrierobotern. "dt-Zeitschrlft f b r industriel le F w t i g u n g " 72 (1982) Yo. '2 3 . 693 ... 696.
121 'Ingt, G.
Diqitale Regelung von AsynchroFmutrjren fur numerisch gesteuertri Fortigungseinrichtungen. Berlin. Heibelberg, New York: SCringrr Yo-lag 1985.
131 Egner, M . , KFupPr. G.
Oigitale nichtlineare Regelungen iund Identifikati3nsverfahren fur elektrohydraul ische Yorschubantriebe. G + P olhydraulik und pnt'umatik 25 (1985! No. 3 , p. 669 ... 677.
/ 4 / Wurst, K.-H..
Gelenkantriebe fur Industrieroboter. "wt-Zeitschrift Fur industrielle Fertigbng" 74 (19M). No. 12 p. 717 ... 720.
Kleckner. J.
/51 Yurst, K.-H.
161 Pritschow, G. Keuner, G.
Elektrischer Kompaktantrleb fdr ~reh-jSchwenkCcwegung. wt-Zeitschrift fur industriella iertigung" (1985; 12, p . 708 ... 710. Elektrchydraulischer Gelenkantrieb fur lndustrieroboter - Anforderungen, Konzeptc und Eealisierung Pines Kompaktantriebes 2 1 s Gc-
lenkachse. R e w i r t s i l i m 7. PFK 1586 Vol. I . ... 293.
P. 272
l i l Stutp, G.. VOst. G.,
Wurst. K.-H.
Figure 12: Elektrohydraulic compact drive as a joint drive In a similar way as in the electrical drive the modules of the electrohydraulic drive fulfill several subfunctions; thus the number of necessary mechanical parts for the realization of all required subfunctions i s reduced. The motor shaft of the blade type motor at the same time represents
-
the the the the the
mechanical parts to transfer the input power guiding mechanism for the hydraulic fluid case of the spool valve of the blade type motor element bearing the spool lands of the spool valve element bearlng the pilot stage the case bearing the electrorwchanical correcting Plement for controlling the valve
In the followlng s m data of the electrical and the hydraulic joint drive are compared.
4
Future Considerations
The appropriate drive modules for a m d u l a r robot system allow the user the construction of a great number of different robot configurations. Above all the design of special-purpose robots wlll be more cost-effective and simpler, because only the relatively cheap links have to be designed. AS a whole the robot 6 s a machine is designed more flexible. The same flexibility is expected
Spindasyn. ein neucr' elektromechanischer Antrieb Linearantrieb fur NC-Werkzeugmaschinen. w t - Z . ind. Fertigung 73 (1983) NO. 3 . D . 169 ... 175.
The idea o f using an industrial robot is to have a flexible machine. adaptable to new tasks It any time without great efforts. But up to now this is only possible with a lot of restrictions. By using both speed-controlled AC drives and hydraulic motors in connection with a state base control the mechanical and the eiectrical components can be put together in a way that the drive is integrated into the robot arm with a minimum of meChdniCa1 parts. By means of special adapters the user is capable t o assemble the robot with the joints and arms on his own. With these components one obtains task-specified robots with free choice In kinematics, torque, Stiffness and path velocity.
lnstitut fur Steuerungstechnik der Werkzeugmaschinen und Fertigungseinrichtungen der Unlversitat Stuttgart, Seidenstrasse 36. 0-7000 Stuttgart 1 1
Device-specific problems in using industrial robots
Industrial robots have found their first use in manufacturing technology in the area of handllng workpieces. where they still are applied to a great extent up to now. In connection with handling always a universal availability was considered t o be most important. In regard to the field of tasks this availability can be fulfilled in a relatively slnple way. although also here one has to take into account that there is only one optimal device construction for one distlnct workp i e c e 3 e c t r e and one task. The most i m p o r t x criteria for the selection of an i n G t r i a l robot for handling are the load and the working range in connection wlth the kinematic structure. For the estimation of robots handling tools or workpieces for manufacturing, criteria are used which among other things are of importance also for the design of machine tools. The process and the requirements to the result of tooling detennine the characteristics of the device. The selection of a robot is made accordlng to the requirements of the procedure a s is shown in Figure 1. Only in very few cases the result is an optimal device, but m c h more a canprmlse of working range. speed, load and rigidity. Frequently, however, overdlrnensioned devices are chosen in order to cover all requirements. Especially when industrial robots are to be used as tooling machines for
Motors, mechanical transfer elernents, links and joints of industrial robots - except the flrst basls axis - belong t o the moving mechanical parts, i. e . the masses of these elements decisively influence the acceleration of the individual axes. The claim for as small masses as posslble can be deduced from this. Nevertheless the structure o f the industrlal robots has to be maintenance-friendly. This can be achieved by the modularization of the construction elements. Especially when us ng y rau Ic drives for industrial robots a corn act construttionh Ps Lquired. This refers essentially to ding mechanism for the hydraulic fluid to the wrists.
6
What results from the claim mentioned above is the requirement to make power density of the drives as high as posslble. The pover spectre o f exlsting drives today includes the range of 100 U (e. g. wrists) up to 10 kW (e. 9. basis axes). The maximum speed of the axes can amount up to ln/s respectively 360. Is for rotational movements. As a rule thls speed 1s to be arrived within a few tenths of a second. lhe angles of rotation for basls axes usually are below 360.. For contlnous path controlled industrial m b o t s often posltioning accuracies of 1/0.05 nn~are required. The speed range ( = ratio of maxirnum to minimum speed) has to be between 100 : 1 for simple handling tasks and 2000 : 1 e. g. for measuring and tooling with the same robot. Besides these requlrements the drives should fulfill the conditions for explosion protection and need as 1Ittle maintenance as possible. 2.2
Drive elements for a modular concept
The drive units of an industrial m b o t hold the biggest share in the costs for the equipment. Therefore they form the main point within the concept for a modular system regarding their modularity and reutilization. At present industrial robots are usually equipped with DC servo drives. Besides high dynamics they have the advantage of
elechohydroulic drim
Figure 1: Applications engineering of robots - grinding. - burrlng. - path welding - coating and varnishing.
d)
there are often difficulties in finding optimally approprlate devices on the market. For the solution o f thls problems special-purpose robots were constructed or existing devices were improved by expensive reconstructions in order to achieve an optimally working robot and its economic use. But further applications In the future will be only cost-effective, if using an appropriate modular robot system, by means of which the user can determine and compose his task-specific robot On his own. 2
Orlves for industrial robots
2.1
Requirements
a,L
rofmy
The drives are subsystems of rentiates between drives for Basis axes mainly serve for Cartesian coordinate system; of the tool.
an industrfal robot. One dlffebasis axes, joints and wrists. reaching polnts described in a wrists serve for the orientation
Annals of the ClRP Vol. 35/1/1986
Figure 2: Drive elements o f a nodular robot system
89
small pulsations in their torque. The speed control is very simply to realize. Disadvantages are the high costs for OC drives, the wear of the comnutator dnd especially the Iimitation of peak torques and speeds by the commutator, which often lead to overdimensioned drives in industrial robots. Due to the progress in the power control and the control of asynchronous and synchronous drives today cost-effectlve drives can be constructed, whose static and dynamic behaviour outperforms that of DC-drlves. Because there is no commutator. they are maintenance-free and possess d high overload capacity. An At motor 1st applied a s drive unit for the modular concept presented. It has a low price, dnd the speed control. whose realization is often considered t o be very expensive. has found a cost-effective solution by using micro computers 121. A l s o the further development of hydraulic drive units and their improvement in their static and dynamic behaviour by state base controls I31 lead t o drive units applicable for a modular system (Figure 2).
3
Elements for modular industrial robots
3.1
Module for linear movements
I n this concept the principle of the
generation of movements is inverted (Figure 2a and 3). The stator of the asynchronous motor is integrated into the supporting slide. The ball screw as a part of tne module is fixed at the engitv foundation. The rotor of the AC motor and the nut are put together as one unit. A digital masurerent equipment for velocity and position feedback is integrated 171. lhe module consisting of ball screw, supporting slide, slideway arid AC motor has the following advantages: - less bearing and no coupling between ball screw and the motor and therefore a high stiffness of the system; - optimal dynamic behaviour as there Is no angular immentum of the ball screw and no critical Speed; - no gear to reduce the angular momentum - increased rigidity of the ball screw because of preloading without problems; - less space required. those of
I
mis 01 symmetry
Figure 4: Drafts of different joint drives In the construction of the joint drive parts of the gear mechanism are parts of the motor at the same time. For thls the stator of the motor is connected wlth one part of the llnk. the other part is connected t o the rotor v i a gears attached on both sides (Figure 5a).
Figure 3: Slide unit of the test drive (seen from below)
A comparison of important data with drive shows the advantages:
b)
0)
Figure 5: a) Joint drive with AC motor and symmetric planet gear b) Prototype The usual couplings between motor and drive are not needed. The measurlng system as a simple pulse generator, which Is also used as a measuring system for the speed, is put on the rotor of the A t motor. In o r d e r to adapt torque and speed planet gears, e. 9. compact drive kits without free motion, type harmonic drive, for wrlsts or eccentric gears for swinging movements are applied. 3.3
Module for rotational and swinging movements
The industrial robot as an open kinematic chain in its most usual kinematics consists of a canbination of rotational and swinging movements. The drive nodule, presented in 3.2, thus is not sufficient for a modular system. Therefore the aim was the realisation of the rotating movement by means of a compact drive in consequent development.
a conventional TW'eh:cI
wrkspcce
31 1
IWC
ljres
votion
conventional drlve with drives integrated nut diameter of ball screw in mn lead of ball screw in mn length o f ball screw in mn mass of slide unit in kg smallest rigidity between motor and tooling point in N/pm realizable velocity gain Kv first mechanical characteristic frequency in Hz 3.2
40
...
50 10
2000 400
25 5 2000 400
15 ... 35 36 ... 66 55 sec-' 100 sec-l
25
... 40
& 40
Module for joint drive
Up to now it is characteristic of jolnts that motor, gear and the measurement equipment for velocity and position feedback are installed seperately on the links (Figure 4). The use of an asynchronous m t o r s allows the installation of motor and gear into the joints of an industrial robot (Figure 5b) in order to create a compact symnetrlcal drive unit of the joint 141. Both this join1 constructions with their relatively high space required and the drive system according to Flgure 4c do not allow an appropriate modular design. This is also the case f o r drive concepts, in which the force is transmitted with hollow shafts, toothed belts ptc.
o=b
1-1
I/-
Figure 6: Approach of the optimal workspace by sqlrared gear configuration
The combinations of the rotating and shinging movements can be shown by a vector 7, which is linked to the point 0 and is revolved round%, andoc,(Figure 6. abcve). The top of the vector here moves on 2 spherical surface. P drive system for these two m o v e w n t s requires a minimum of space. if all its lie within tbis Sphere (theoretically degenerated e:ement t o a point !. With q u a ! requirements to Dcth dies, the minimum space required i s best approximated by a configuration of inside iFigurF 6. differential gears with the motors si!ua!ed below). FFW the symmetrical configuration of t h e motor and the geirr i n the ]Gint advantages result dhich are i i i I i 5 ! also for the fcint drive in 3.2 (Figure 7 ) .
I
.. --__--
II
Figure 9: Modular industiisl robot with three drive units
.
LZZYNW
T7+ **" n&
pJd~dlm#fmt
.\
\
sro*mOrnl
Figure 7 Opsign of a realized j o i n t W:ve
o m b r mde
The integration of tho rnotnrs r h e m s e l w s effects an i n r r e i s e of the mais of the joint. but only in the range of about 1G %. Figure 8 shows a drivp scdule f o r a wrist. Some data verify
the C@mpdCt s?ructure o f thP wrist ma52 included odzpter Jnit diameter o f an enveiopc sphere rated torque f o r rotat\ng or s w i nqi rig movements 2ngular delocity for Mnrrax
:Z kg about i 7 0 mn
F
i
MHrar 0
-
= 60 Nm 9Co/iec
Far the combinpd movement rotating and swinging there I F a separation of t h e power. The drive modules c r e ecuipped with adapters (Figure 8b), whose structure allows to connect the modules and links very quickly with reproducih!e accuracy v i a a s ~ e c i a lclamping d ~ v i c e . In c a r p of need the power s i m p l y i n g lines ml the medns o f process can be guided thrcjuqh tne rnodule.
\
Figure 10: Example of mlulf applica' Module for loint drives on the basis of electrohydraulic 3.4
!notars
In grder to be competitive with the electrical drives mentioned above. modular electrohydraulic drlves In industrial robots must possess a comparable static and dynamic behaviour with ecjual modularlty, lower price and smaller construction vnlume. Esbecially fur firidncial redsons and from points uf vile o f optimal energy utilization therefore only direct drives without further mechanical transfer elements, e. g. gears, cnme intc question. With the restriction to drives with a 1 1 mited regulating range these are:
- tne linear hydraulic actuator fnr the realization of linear movements,
- the blade type motor for the realization of swinging movements.
In d similar way as the joint drive described in 3.2 a drive unit with blade type mator is appropriate as modular a component. Blade type motors have a relatively small rlgldity as is the case in linear hydraulic actuators. Certainly this is a disadvantage and a problem of these motors. These problems can be solved. however. by means of intelligent and effective control systems. Figure 1 1 shows the structure of a discrete state base control for a linear hydraulic actuator, which can be used in the same way for controlling a blade type motor. a)
b)
Figure 8: Actuator module as a wrist a) wrist b) adapter How to compose a complete robot with 6 degrees of freedcm with three drive modules is shown in Figure 9 151. I t makes clear that also kinematically overdimensioned systems, mainly f o r the extension of the working range and adaption, can be rnalized without DrObleInS.
Figure 10 shows how to use the module for the combinations o f the movements 'translation' and 'swinging'. For this the rotating axis is connected with a steering rack via a pinion. A s mechanical transfer element for the linear movement belts or ba!l screws can ! ~ nused, too.
toothed
For the reduction of the nwasuring expenditure state base observers are used. Linear state base controls enable a high ve!OCity gain (Kv) in the range of 100 11s f o r a linearized dorking range o f the non-linear controlled system. The high parameter sensitivity of state base controls with high gain o f the control loop, however, requires the adaption of the control and observer parameters. in order to achieve a good control behaviour in the complete working range of the drive. The control structure shown in Figure 11 and realized on the basis of d micro computer effected a velocity gain at a servo hydraulic drive which was 5 times higher than controlled with a ronventional P-algorithm 131. The necessity and the possibilities of a control realized digitally - on the basis of a computer - becane evident in this mamole. Today it is indispensable for controlling robot drives, because in addition one has to take into account mechanlcal feedbacks due to elastic couplings of further drive units as well as the m n t of inertia which changes with the position o f robot.
91
also of the robst control, in arder to adapt the COntrClS to the possible configurations simoly by t h e inlut Cif *.he r3bTt kinematics v i a parameters. ~iterature /I/
I
'lil>I'
1 1 II
Figure 1 1 : Structure of an adaptive state base control for electrohydraulic drives I31 In order to achieve a compact construction of the joint drive, the blade type motor. the bearing parts of the joint, the v a l ve and the elements for power supply have to be arranged i n a way that saves costs and weight. The prototype of such a drive is presented in Figure 12 161.
WlJPSt.
U.-H.
Dberfltichenschleifen mit HiIfe d c l n Industrierobotern. "dt-Zeitschrlft f b r industriel le F w t i g u n g " 72 (1982) Yo. '2 3 . 693 ... 696.
121 'Ingt, G.
Diqitale Regelung von AsynchroFmutrjren fur numerisch gesteuertri Fortigungseinrichtungen. Berlin. Heibelberg, New York: SCringrr Yo-lag 1985.
131 Egner, M . , KFupPr. G.
Oigitale nichtlineare Regelungen iund Identifikati3nsverfahren fur elektrohydraul ische Yorschubantriebe. G + P olhydraulik und pnt'umatik 25 (1985! No. 3 , p. 669 ... 677.
/ 4 / Wurst, K.-H..
Gelenkantriebe fur Industrieroboter. "wt-Zeitschrift Fur industrielle Fertigbng" 74 (19M). No. 12 p. 717 ... 720.
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/51 Yurst, K.-H.
161 Pritschow, G. Keuner, G.
Elektrischer Kompaktantrleb fdr ~reh-jSchwenkCcwegung. wt-Zeitschrift fur industriella iertigung" (1985; 12, p . 708 ... 710. Elektrchydraulischer Gelenkantrieb fur lndustrieroboter - Anforderungen, Konzeptc und Eealisierung Pines Kompaktantriebes 2 1 s Gc-
lenkachse. R e w i r t s i l i m 7. PFK 1586 Vol. I . ... 293.
P. 272
l i l Stutp, G.. VOst. G.,
Wurst. K.-H.
Figure 12: Elektrohydraulic compact drive as a joint drive In a similar way as in the electrical drive the modules of the electrohydraulic drive fulfill several subfunctions; thus the number of necessary mechanical parts for the realization of all required subfunctions i s reduced. The motor shaft of the blade type motor at the same time represents
-
the the the the the
mechanical parts to transfer the input power guiding mechanism for the hydraulic fluid case of the spool valve of the blade type motor element bearing the spool lands of the spool valve element bearlng the pilot stage the case bearing the electrorwchanical correcting Plement for controlling the valve
In the followlng s m data of the electrical and the hydraulic joint drive are compared.
4
Future Considerations
The appropriate drive modules for a m d u l a r robot system allow the user the construction of a great number of different robot configurations. Above all the design of special-purpose robots wlll be more cost-effective and simpler, because only the relatively cheap links have to be designed. AS a whole the robot 6 s a machine is designed more flexible. The same flexibility is expected
Spindasyn. ein neucr' elektromechanischer Antrieb Linearantrieb fur NC-Werkzeugmaschinen. w t - Z . ind. Fertigung 73 (1983) NO. 3 . D . 169 ... 175.