Tool holder for manipulator arm

A tool holder for a manipulator comprises a tool shaft extending along and rotatable about a main axis and having a tool-shaft end provided with a pivot defining a transverse axis. A tool is carried on the pivot and is displaceable relative to the tool shaft about the transverse axis. A stack of guide rings coaxially surrounds the tool shaft adjacent the pivot and is formed with at least two throughgoing guide-ring passages each having a radially outwardly opening passage end. Two of the guide rings define a pair of axially spaced annular confronting guide-ring surfaces. A connector ring is rotatable on the stack between the guide-ring surfaces and has a pair of axially oppositely directed connector-ring surfaces one of which axially directly confronts one of the guide-ring surfaces. A connector element secures the connector ring to the tool-shaft end for joint rotation of same about the main axis. A flat contact element is secured to one of the one surfaces and is axially flatly engageable with the other of the one surfaces. Thus current can be transmitted between the connector ring and the guide ring of the one guide-ring surface by the contact element. A piston-and-cylinder assembly and a spring are engaged between the connector ring and the other of the guide-ring surfaces for pressing the one surface and contact element together axially. An electrical feed line is connected to the conductor fixed to the support and an electrical line is connected between the other conductor and the tool for feeding electricity through to the tool.

FIELD OF THE INVENTION 
The present invention relates to a tool holder for a manipulator arm. More 
particularly this invention concerns such a tool holder that is used on a 
robot welder. 
BACKGROUND OF THE INVENTION 
A tool holder for a manipulator is known which comprises a tool shaft 
extending along and rotatable about a main axis and having a tool-shaft 
end provided with a pivot defining a transverse axis. A tool is carried on 
the pivot and is displaceable relative to the tool shaft about the 
transverse axis. A support adjacent the tool carries one of a pair of 
mutually engageable conductors, the other of which is fixed on the 
tool-shaft end so as to be movable therewith. An electrical feed line is 
connected to the conductor fixed to the support and means including an 
electrical line is connected between the other conductor and the tool for 
feeding electricity through to the tool. 
It is known from German patent document 2,416,536 to use a semicylindrical 
contact shoe centered on the main axis and surrounded by angularly 
extending flexible commutators which are tensioned radially in against an 
outer surface of the contact shoe. It is also known from U.S. Pat. No. 
2,879,490 to employ a pair of contact shoes that are biased radially 
inwardly against a cylindrical outer conductor surface by powerful 
radially extending screws. Another system seen in U.S. Pat. No. 2,341,459 
has two relatively rotatable conductors with axially confronting and 
abutting faces which are biased axially together by springs and the force 
of a pneumatic cylinder to form a good electrical connection. 
In addition it is frequently desired to make fluid connections to the tool, 
which frequently itself has to be cooled, or to a fluid cylinder in the 
tool for minor displacements of the tool. This is particularly the case 
with tong-type pinch welders and the like. As the tool is frequently 
rotated a full 360.degree. to make an annular weld seam, it is necessary 
to provide complex fluid lines. These even further complicate the problem 
of conducting electricity through the holder. 
OBJECTS OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
tool holder for a manipulator. 
Another object is the provision of such a tool holder for a manipulator 
which overcomes the above-given disadvantages. 
A further object is such a tool holder which comprises a few basic elements 
that can be assembled together to meet the requirements of all types of 
tools, from simple ones needing nothing more than one electrical and two 
fluid--that is hydraulic or pneumatic--connections, to more complex ones 
needing two electrical and four fluid connections. 
SUMMARY OF THE INVENTION 
These objects are attained according to the instant invention in a holder 
of the above-described general type, but which has a stack of guide rings 
coaxially surrounding the tool shaft adjacent the pivot and formed with at 
least two throughgoing guide-ring passages each having a radially 
outwardly opening passage end. Two of the guide rings define a pair of 
axially spaced annular confronting guide-ring surfaces. A connector ring 
is rotatable on the stack between the guide-ring surfaces and has a pair 
of axially oppositely directed connector-ring surfaces one of which 
axially directly confronts one of the guide-ring surfaces. Connector means 
secures the connector ring to the tool-shaft end for joint rotation of 
same about the main axis. A flat contact element is secured to one of the 
one surfaces and is axially flatly engageable with the other of the one 
surfaces. Thus current can be transmitted between the connector ring and 
the guide ring of the one guide-ring surface by the contact element. Means 
including a piston-and-cylinder assembly and a spring is engaged between 
the connector ring and the other of the guide-ring surfaces for pressing 
the one surfaces and contact element together axially. 
The advantage of this system is that a part which is fixed to the input 
side and a part which is fixed on the output side of the holder, but 
rotatable relative to the input-side part are used to conduct electricity 
and, if desired, fluids through the holder to the tool. The use of a stack 
of rings makes it possible, as will be explained further below, to 
increase the connections through the holder with ease. 
According to this invention the guide rings are formed with complementary 
coaxially centered formations fitting into one another, whereby the stack 
forms a tube around the tool shaft. Thus they will be perfectly concentric 
and axially fixed with respect to one another. 
In accordance with another feature of this invention the 
piston-and-cylinder arrangement includes an annular cylinder ring secured 
to one of the guide rings and forming the other of the guide-ring surfaces 
and an annular piston axially displaceable in the cylinder ring. Such 
arrangement is almost foolproof and allows considerable force to be 
brought to bear for best electrical contact. This piston-and-cylinder 
assembly is braced axially between the connector rings. 
In a system where the tool requires two electrical feeds, the holder 
further comprises a second such connector ring axially sandwiched with the 
first-mentioned connector ring between the guide-ring surfaces, a second 
such flat contact element between the guide ring of the other of the one 
guide-ring surfaces and the confronting surface of the second such 
connector ring and secured to one of same, a second such electrical 
conductor connected to the guide ring of the other guide-ring surface and 
a second such electrical line connected between the second connector ring 
and the tool, and a second such connector means for securing the second 
connector ring to the tool-shaft end for joint rotation with same about 
the main axis. Thus it is possible to use a two-part tool for pinch or 
spot welding. 
The flat contact element according to this invention is formed by an 
annulus of angularly spaced conductive contact segments separated by 
axially open gaps. Thus any foreign matter that finds its way in between 
the contact-element face and the ring face it axially flatly abuts will be 
scraped from the contact segments into the gaps. The contact element 
segments are each at least one terminal-silver plate having a planar face 
and soldered to the one of the one surfaces. 
According to this invention at least some of the guide rings are of light 
metal with hard insulating coatings. Thus even though all of these rings 
are rigid metal elements, they can be axially bolted together without fear 
of their shorting out. It is possible to take the assembly according to 
this invention apart relatively easily when the guide ring of the one 
guide-ring surface has inner and outer parts interengaging each other by a 
screwthread for limited axial displacement of the outer part on the inner 
part. The outer part can therefore be screwed up to clamp the assembly 
axially together, to which end it normally comes into flat contact with a 
shoulder of the inner part that defines its end position. 
When according to this invention when the tool requires two fluid feeds the 
holder further comprises a second such connector ring axially sandwiched 
with the first-mentioned connector ring between the guide-ring surfaces. 
In this case the stack is formed with another two throughgoing guide-ring 
passages each having a passage end opening radially outwardly level with 
the second connector ring and the second connector ring is formed with 
connector-ring passages radially aligned with the other two guide-ring 
passages. This holder further has a second such connector means for 
securing the second connector ring to the tool-shaft end for joint 
rotation with same about the main axis, and means including fluid lines 
connected between all four of the connector-ring passages and the tool for 
feeding respective fluids through the connector rings to the tool. Thus 
with this system a tool that is carried on a double-acting cylinder can 
have two connections for this cylinder and two for circulating coolant 
through the tool. In this case the connector-ring passages include 
radially inwardly open guide grooves aligned with the respective passage 
ends. 
It is also possible according to this invention for the one surfaces to be 
axially spaced and have chamfered outer edges. The holder further 
comprises an O-ring engaging radially inwardly against the chamfered 
edges. In this manner dirt is prevented from entering this gap between 
these one surfaces in a manner which offers virtually no resistance to 
relative rotation of the two parts it engages, while permitting limited 
relative axial motion between these parts.

SPECIFIC DESCRIPTION 
As seen in FIG. 1 a welding tool 23 is carried at the outer end of an arm 
42 carried on an axle 36 centered on an axis A' and journaled in cheeks 54 
carried on a flange 50 formed at the end of a tube shaft 24 extending 
centered on an axis A perpendicular to the axis A'. A shaft 34 coaxially 
through the center of this tube shaft 24 carries a bevel gear 35 meshing 
with another bevel gear 35 fixed on the axle 36. Thus joint rotation of 
the shafts 24 and 34 about the axis A will rotate the welding tool 23, 
here constituted by a hollow coolable electrode 43, about the axis A; 
relative rotation of the shafts 24 and 34 about the axis A will displace 
this tool 23 angularly about the axis A'. This style of movement is 
similar to that described in my U.S. Pat. No. 4,290,239. The illustrated 
assembly is normally carried at the end of a manipulator arm of the type 
described in that patent or in my copending U.S. patent application Ser. 
Nos. 267,756 filed May 28, 1981 (now U.S. Pat. No. 4,399,718) or 326,762 
filed Dec. 2, 1981. 
The assembly of this invention has an outer support tube shaft 12 centered 
on the axis A and carrying at its lower end a fixed ring 44 to which is in 
turn fixed an externally threaded support ring 37. An intermediate guide 
ring 15 is fixed atop this ring 37, and another guide ring 13 is fixed 
atop its, with shoulders 45 on the rings 37 and 15 centering the rings 15 
and 13, respectively. Thus the tube shaft 12, ring 50, ring 37, ring 15, 
and ring 13 are all fixed relative to each other, effectively forming a 
tube centered on the axis A. This assembly can simply be the last element 
or "wrist" of a manipulator arm. The upper ring 13 is of L-section and has 
an axially opening port 13a to which compressed air can be fed through a 
line indicated schematically at 7. 
Threaded up against a shoulder 38 of the lower guide ring 37 is a ring 30 
to which in turn is soldered a plurality of flat contact elements 9 of 
so-called terminal silver. This ring 30 is in excellent electrical contact 
with the lower ring 37 which in turn is connected to an electrical feed 
wire 1. Another feed wire 2 of opposite polarity is connected to a support 
55 on which workpieces W to be welded are carried. At least the rings 15 
and 44 are of aluminum with hard anodized insulating coatings, so that the 
rings 30 and 37 are electrically isolated from the rest of the structure. 
Similarly making the rings 13 of hard-coated aluminum or light metal also 
can avoid the possibility of an electrical connection at a fluid line. 
Rotatable on the ring 15 is another ring 28 having a flat bottom surface 
engageable flatly with the contact segments 9 and a flat top surface 
engaging the face of a piston 10 which is axially displaceable in a 
cylinder groove 39a of a ring 39 engaged under the radial leg of the 
L-section ring 13. Springs 11 urge the piston 10 axially downwardly into 
engagement with the top surface of the ring 28 to press it down against 
the segments 9. In addition compressed air fed in through the port 13a in 
the ring 13 can pressurize the groove 39a above the annular piston 10 to 
press it down with considerable force, thereby forcing the ring 28 into 
excellent electrical contact with the contact segments 9. The rings 28, 
30, and 39 are spaced apart by gaps 48 and have chamfered edges 47 in 
which O-ring type seals 49 are provided to keep foreign matter out of the 
assembly. 
A flexible heavy-duty cable 1' is connected at one end to the ring 28 and 
at the other end to the electrode 43 so that current can flow from the 
line 1 through the rings 37 and 30, contact segments 9, ring 28, and wire 
1' to the electrode 43. The flexibility of the wire 1' allows the tool 23 
to move about the axis A' relative to the ring 28. Obviously the electrode 
43 is insulated in a conventional manner from the rest of the assembly. An 
entrainment element or arm 26 is fixed at one end to the ring 28 and at 
its other end via a key 25 to the flange 50, which key 25 allows limited 
relative displacement between the flange 50 and ring 28. In this manner 
the ring 28 rotates jointly with the flange 50 and shaft 24. 
The rings 13 and 15 are formed with passages 3 and 4 opening axially 
upwardly and radially outwardly at radially spaced locations. Respective 
radially inwardly open grooves 19 and 20 are formed in the ring 28 aligned 
with the radially outwardly open ends of the passages 3 and 4. In turn 
passages 3' and 4' and flexible lines 3" and 4" lead from these grooves 19 
and 20 to the coolable electrode 43. Thus a coolant fed into the upper end 
of the passage 3 will pass radially out through the groove 19 to the 
passage 3' and line 3" to the electrode 43 to cool it, then will return 
via the line 4", the passage 4', the groove 20, and the passage 4. This 
flow is possible in any angular position of the ring 28 relative to the 
rings 15 and 13. 
With the system according to the instant invention air pressure need only 
be applied through the line 7 to the piston 10 when electricity is to pass 
between the cables 1 and 1'. Thus if the welder is only used when it is 
stationary, the joints and bearings can be relieved of the axial load 
created by the piston 10 in the assembly as it is moved from place to 
place. The cylinder 39a above the piston 10 is only pressurized when 
current is to flow and the device is stationary. The pressure brought to 
bear can be considerable to ensure an excellent electrical connection 
between the segments 9, which obviously could be bonded to the lower face 
of the ring 28 if desired, and whichever of the two rings 28 or 37 it is 
movable with respect to. 
FIG. 2 shows an arrangement having the above-described couplings for a 
coolant and a connection for a single electrical pole, but in addition has 
two extra connections for hydraulic or pneumatic feed and return lines. 
More particularly in the arrangement of FIG. 2, where reference numerals 
and letters identical to those of FIG. 1 refer to functionally equivalent 
structure, the connector 26' has a lower portion 26a formed as a radial 
continuation of the flange 50 and supporting a ring 27 formed with a pair 
of radially inwardly open grooves 17 and 18. The connector 26' has an 
upwardly extending arm 26b that is connected to this ring 27, and to the 
ring 28 as in FIG. 1. In addition the tube shaft 12 carries a bottom guide 
ring 16 axially level with the extra ring 27. 
The guide rings 13, 15, 37, and 27 are formed with two further passages 5 
and 6 which open axially upwardly at the top ring 13 and radially from the 
ring 6 level with the passages 17 and 18, respectively. The grooves 17 and 
18 in turn are connected to passages 5' and 6' in turned connected to 
flexible tubes 5" and 6" connected to the opposite compartments of a 
double-acting cylinder 51 having a piston 51a with a piston rod 51b that 
carries a welding tool 40 having a cooled electrode 41 that is connected 
via the tubes 3" and 4" to the passages 3', 4' and thence via the passages 
3 and 4 to the source of coolant as in FIG. 1. In this manner 
pressurization of either of the compartments defined in the cylinder 51c 
by the piston 51a with simultaneous venting of the other compartment can 
move the electrode along axis A' limitedly in either direction. 
FIG. 3 shows an arrangement that is one step more complex than that of FIG. 
2. Here provision is made for connection to a second electrode. 
More particularly one electrode 32 is carried on the piston rod 51b and 
another electrode 33 is carried on an arm 51d extending downwardly from 
the cylinder 51c. Thus as the piston 51a slides along axis A' in its 
cylinder 51c it can bring the two welding tools 32 and 33 together or 
separate them. This is a typical pinch-weld arrangement for a robot spot 
welder. 
The tool 32 is connected via the line 1' to the ring 28 as in FIG. 1. The 
device here is equipped with a second current-conducting ring 29 above the 
ring 28. Secured underneath the ring 13, but insulated from it, is another 
ring 31 and the piston 10 is provided in the ring 29, bearing axially 
downwardly on the top of the ring 28. Further contact segments 8 are 
provided on the lower face of the ring 31 to which the second electric 
feed cable 2 is connected directly. The piston 10 is constructed as 
described above of aluminum with a hard insulating coating, e.g. an 
anodized finish, so that it does not form a conductive bridge between the 
rings 28 and 29. 
In addition the system is provided with another guide ring 14 between the 
ring 13 and the ring 15. The rings 13, 14, and 15 are formed with the 
passages 3-6 described above, and with the passage 7 that here opens 
radially in the ring 14 level with a radially inwardly open groove 21 
connected to the compartment 39a behind the annular piston 10 in the ring 
29. Another such groove 22 in the ring 29 opens level with the end of the 
passage 4, and the passage 4' is here partially formed in the ring 29. The 
passage 3 opens into the groove 19 and the groove 20 is not used. 
In this arrangement cylinder 39a behind the piston 10 can be pressurized 
via the passage 7 to press the two rings 28 and 29 apart and into contact 
with the respective segments 9 and 8. This ensures excellent contact 
between the rings 30 and 31 and the rings 28 and 29, thereby connecting 
the cables 1 and 2 firmly to the electrodes 32 and 33. 
It would also be possible in this arrangement to replace the two electrodes 
32 and 33 with electrodes 52 pressing a workpiece W against a conductive 
support 53. 
FIG. 4 shows how the segments 9 are separated by gaps 46. In this manner 
any foreign matter that comes between the segments 9 and the surfaces 3 
will inherently be swept into these gaps and will not score the segments. 
A good electrical contact at all times is thus ensured along with a long 
service life for the equipment. 
The system therefore allows the tool to revolve at will about the axis A 
relative to the support without in any way interfering with the electrical 
and fluid connections. The system can furthermore be easily adapted by use 
of the necessary connector rings to connect up any normally desired amount 
of electrical and fluid connections.