Testing unit for rotary shaft encoders

The present invention is a portable testing apparatus for field testing rotary shaft encoders. The rotary shaft encoder is mounted in connection to a motor disposed on a mounting panel whose direction and speed of rotation is controlled by a motor controller. The rotatable shaft of the rotary shaft encoder is coupled to the motor shaft via a shaft couple. A multiple wire connector is employed to connect to the plurality of connection wires of the rotary shaft encoder. Each connection wire of the rotary shaft encoder is connected to one of a plurality of single pole, multiple throw load selection switches. Thius permits connection of an operator selected one of a predetermined set of voltages and loads to each connection wire of the shaft encoder forming a circuit simulating its use. An output terminal connected to each connection wire of the rotary shaft encoded permits the signal on these corresponding connection wires to be monitored. In the preferred embodiment the testing apparatus is mounted in an attache which may be closed for transport and opened for use.

TECHNICAL FIELD OF THE INVENTION 
The technical field of the present invention is that of testing 
apparatuses, and more particularly portable testing apparatuses for rotary 
shaft encoders. 
BACKGROUND OF THE INVENTION 
Rotary shaft encoders are devices which are employed to indicate the motion 
of parts of machinery. In particular, rotary shaft encoders are widely 
employed to measure the motion of the joints in robotic machinery. With 
the rise in the employment of robotics in manufacturing, such rotary shaft 
encoders have become very widely employed. 
There is a problem related to the extensive use of such rotary shaft 
encoders when there is some failure in the operation of the robot or other 
controlled machine which employs such rotary shaft encoders. In many 
instances the shaft encoder is suspected in the failure. Currently, there 
is no reliable and proven method for testing such rotary shaft encoders to 
determine whether the machine failure is due to a failure in the shaft 
encoder. There are two primary solutions attempted to this problem, each 
having significant drawbacks. 
In a first attempt to solve this problem service involves testing the 
rotary shaft encoder in place. An oscilloscope probe or the input probe of 
some other monitoring device is attached to the output lines of the rotary 
shaft encoder while the rotary shaft encoder is in place within the 
controlled machine. Then the joint is moved, either by hand or via a 
controlled movement by the machine itself. This technique is not 
satisfactory for several reasons. Firstly, it is difficult and sometimes 
dangerous to attach the oscilloscope probes to the rotary shaft encoder 
outputs while in place in the machine. In addition, attempting to move the 
machine to generate the shaft encoder outputs for testing may be difficult 
or impossible, particularly in light of the fact that the controlled 
machine is out of order in some manner. Lastly, it is possible that the 
fault is not in the shaft encoder but rather in the machine itself. For 
example, if the rotary shaft encoder is not supplied with the proper 
working voltages or if the outputs are improperly loaded, the output of 
the rotary shaft encoder will appear incorrect even though the fault is in 
other parts of the machine and not in the rotary shaft encoder. 
The second manner of testing of such rotary shaft encoders in the prior art 
requires removal of the rotary shaft encoder from the controlled machine. 
In this case, the rotary shaft encoder is set up on a laboratory bench and 
supplied with proper working voltages. As in the previous case, the 
outputs of the rotary shaft encoder are applied to an oscilloscope or 
other monitoring apparatus to determine whether or not they are proper. In 
most cases the operator attempts to simulate the operation of the machine 
by spinning the shaft of the rotary shaft encoder by hand while 
simultaneously attempting to observe the output on the oscilloscope. Such 
a test procedure is often a jerry-rigged affair with the supply voltages 
and the outputs being connected in a rat's nest of wires. This leads to 
the introduction of external noise or static and to unreliable connection 
to the rotary shaft encoder. In addition, it is impossible to reliably 
turn the shaft encoder in a manner enabling the proper observation of its 
output when using this technique. Lastly, the outputs of the rotary shaft 
encoder are not loaded in the same manner as they would be loaded when 
employed in the controlled machine. It is possible for the outputs of the 
rotary shaft encoder to appear correct when tested in this manner, whereas 
the rotary shaft encoder will fail when required to drive the load in the 
controlled machine. 
I n view of the foregoing it would be advantageous in the art to provide a 
manner for reliably and easily testing rotary shaft encoders on the 
workshop floor. 
SUMMARY OF THE INVENTION 
The present invention is a testing apparatus for rotary shaft encoders 
which can be reliably employed on the shop floor. The rotary shaft encoder 
is removed from the controlled machine which employs this encoder. The 
rotary shaft encoder is then held in a test fixture in a predetermined 
location and orientation. The shaft of the rotary shaft encoder is coupled 
to the shaft of a controlled motor. The holding fixture preferably has 
some means for adjusting the relationship of the rotary shaft encoder to 
the motor in order to properly match the length of shafts of these 
devices. The various inputs and outputs connected to the rotary shaft 
encoder are coupled to the testing apparatus via the coupling device which 
was employed for use of the rotary shaft encoder. Such rotary shaft 
encoders often include a multi-pin connector for connection of the rotary 
shaft encoder into the circuit of the controlled machine. The testing 
apparatus of the present invention employs this same connector for 
electrical coupling to the rotary shaft encoder. 
A panel of switches enables connection of the proper voltage or the proper 
load to each wire of the rotary shaft encoder via this connector on the 
shaft encoder. In accordance with the preferred embodiment, the tester 
includes a number of power supplies producing. voltages such as 5 volts, 
12 volts, 15 volts and 24 volts DC. It has been found that these are the 
most widely employed voltages for driving such rotary shaft encoders. In 
addition, each such switch has the capability of applying one of a 
plurality of load resistors to the particular connector. Thus, for 
example, any output from the rotary shaft encoder can be connected to the 
desired load. In addition, it is preferable that this load resistor be 
able to be connected to a pull up voltage corresponding to any one of the 
supply voltages provided by the tester or to ground. This permits the 
output of the rotary shaft encoder to be connected to any of the usual 
type of loads normally employed with these outputs. Each of these switches 
is also associated with an output jack which enables an oscilloscope probe 
or other monitoring apparatus to be connected to that particular wire of 
the rotary shaft encoder. 
The tester of the present invention is employed as follows. Firstly, the 
rotary shaft encoder in question is disconnected and removed from the 
controlled machine. Next, this rotary shaft encoder is connected in place 
in the tester. In this regard, the body of the encoder is fixed in place 
and the shaft of the encoder is connected to the shaft of the driving 
motor. Then a multiple wire connector is connected to the normal connector 
of the rotary shaft encoder used to couple it to the apparatus which 
employs it. This coupling enables each wire of the rotary shaft encoder to 
be coupled to one of the multiple position switches. Next, the position of 
the multiple position switches is adjusted in order to apply the proper 
voltage, or load to each connector. In particular, it is possible that the 
rotary shaft encoder requires one or more driving voltages for operation 
on certain of its lines and generates its output on certain other of its 
lines. As a result of this positioning of the multiple position switches, 
the rotary shaft encoder is now coupled into a circuit which simulates the 
circuit employed during its operation. In addition, certain of the wires 
of the rotary shaft encoder are connected to an oscilloscope or other 
monitoring apparatus via the output jacks associated with each multiple 
position switch. The direction and speed of rotation of the shaft of the 
rotary shaft encoder is controlled via a motor controller connected to the 
motor which provides rotary torque to the shaft of the rotary shaft 
encoder. This rotary torque applied by the motor simulates the motion 
measured by the rotary shaft encoder during operation. As a consequence, 
the outputs can be monitored via the. oscilloscope or other monitoring 
apparatus to determine whether or not the rotary shaft encoder is 
operating properly. 
In accordance with the present invention, all of these parts including the 
holding fixture, the multiple power supplies, the motor and motor 
controller, and the multiple position switches are disposed in a portable 
suitcase. As such, this shaft encoder testing apparatus is suitable for 
transportation to the machine which employs the rotary shaft encoder, 
thereby reducing the amount of time required for servicing the rotary 
shaft encoders of that machine. 
In a further embodiment of the present invention, the suitcase apparatus 
includes a small oscilloscope which can be selectively connected to each 
of the multiple position switches. Therefore, the complete apparatus for 
testing the rotary shaft encoder can be transported in one package.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 is a schematic diagram of a first embodiment of the present 
invention. FIG. 1 illustrates the major electrical parts in this first 
embodiment of the present invention. The testing apparatus 100 is coupled 
to an AC power source 10 which supplies the electric power for running 
each of the parts of testing apparatus 100. This electric power is 
switched via AC power switch 105. AC power is connected to motor 
controller 110 and to first power supply 121, second power supply 123, 
third power supply 125 and fourth power supply 127. 
Motor controller 110 is employed to control the rate of shaft rotation of 
rotary shaft encoder 20. Motor controller 110 is coupled to motor 115 and 
is controlled by direction switch 111 and speed control potentiometer 113. 
Motor controller 110 applies the appropriate voltages to motor 115 to 
control the direction and speed of rotation of shaft 116 of motor 115. 
Direction control 111 determines whether the shaft 116 of motor 115 
rotates clockwise or counter-clockwise. Likewise, speed control 
potentiometer 113 controls the speed of operation of motor 115. 
Shaft 116 of motor 115 is coupled to shaft 23 of rotary shaft encoder 20 
via a shaft coupling means 117. This shaft coupling means 117 is further 
illustrated in FIG. 4. Because of this coupling between shaft 116 of motor 
115 and shaft 23 of rotary shaft encoder 20, direction switch 111 and 
speed control potentiometer 113 control the direction and speed of 
rotation of shaft 23 of rotary shaft encoder 20. This in turn controls the 
output produced by rotary shaft encoder 20 on output connector 27. 
Testing apparatus 100 includes four direct current power supplies. In 
accordance with the preferred embodiment of the present invention, these 
four direct current power supplies supply direct current. voltages 
corresponding to the DC voltages required by most of the rotary shaft 
encoders which are likely to be tested with the testing apparatus 100. In 
accordance with the preferred embodiment of the present invention, first 
power supply 121 generates 5 volts DC; second power supply 123 generates 
12 volts DC; third power supply 125 generates 15 volts DC; and fourth 
power supply 127 generates 24 volts DC. The outputs from each of the power 
supplies 121 through 127 is coupled to contacts of a number of switches. 
Switch 129 selects one of the power supply voltages or ground for 
application to one end of a set of load resistors, in a manner that will 
be more fully disclosed below. Volt meter selection switch 135 selects one 
of these voltages to be applied to volt meter 130. Volt meter 130 is 
employed to monitor the output voltage of a selected one of the power 
supplies 121 through 127 in accordance with the position of switch 135. 
This enables the user of testing apparatus 100 to determine whether or not 
the particular power supply selected is generating the appropriate 
voltage. Each of power supplies 121, 123, 125, and 127 is connected to a 
plurality of selection devices 140 in a manner that will be more fully 
explained below. 
The connector 27 of rotary shaft encoder 20 is connected to one end of 
cable 420 via a connector 423. The other end of cable 420 is connected via 
a connector 425 to a connector 245 mounted on the testing apparatus 100. 
Each of the lines in cable 247 is connected to a selection device 140. 
FIG. 1 illustrates only one of these selection devices 140, because they 
are identical except that they are connected to differing conductors of 
cable 247. 
Selection device 140 is employed to couple the appropriate voltage or load 
to the particular line of shaft encoder 20, and to enable connection to an 
external monitoring apparatus." Selection device 140 includes a single 
pole multiple position switch 141 which is shown as connectable to one of 
twelve differing switch positions. In accordance with the preferred 
embodiment of the present invention, switch 141 can switch between twelve 
positions as follows: (1) no load; (2) a first pull up resistor 143; (3) a 
second pull up resistor 145; (4) a third pull up resistor 147; (5) ground; 
(6) first power supply 121; (7) second power supply 123; (8) third power 
supply 125; and (9) fourth power supply 127. In the illustrated embodiment 
positions 10, 11 and 12 of switch 141 are not connected, however, those 
skilled in the art would appreciate that these positions can be employed 
for other voltages or. loads. In accordance with the preferred embodiment 
of the present invention, load resistor 143 is 470 ohms, load resistor 145 
is 1 K ohms and load resistor 147 is 10 K ohms. Thus, the connections of 
multiple position switch 141 are as shown in Table 1. With the exception 
of the not connected positions 10 to 12, this order of circuits connected 
to the switch positions is a safety feature of the present invention. The 
order is from connections which are least dangerous to the rotary shaft 
encoder (position 1, no load), through connections which have a greater 
potential for damage to the rotary shaft encoder (positions 2 to 4, the 
various load resistors; position 5, ground) to connections that have the 
highest potential for damage to the rotary shaft encoder (positions 6 to 
9, increasing level voltage sources). It is contemplated that the switches 
141 will be reset to position 1 after each test, and rotated from position 
1 to the position required for the particular rotary shaft encoder being 
tested. In this manner, inadvertent untimely actuation of AC line switch 
105 has the least potential for damaging the rotary shaft encoder. 
TABLE 1 
______________________________________ 
Switch 
Position Connection 
______________________________________ 
1 no load 
2 470 ohm load resistor 
3 1K ohm load resistor 
4 10K ohm load resistor 
5 ground 
6 +5 volt DC 
7 +12 volt DC 
8 +15 volt DC 
9 +24 volt DC 
10 no connection 
11 no connection 
12 no connection 
______________________________________ 
The testing apparatus 100 of the present invention is employed as follows. 
Firstly, the rotary shaft encoder is removed and disconnected from the 
equipment which employs this shaft encoder. The rotary shaft encoder 20 is 
then inserted in a test fixture included within testing apparatus 100 and 
secured. The shaft 23 of the shaft encoder 20 is secured to motor shaft 
116 via coupling apparatus 117. This ensures that torque developed by 
motor 115 is employed in rotating the shaft 23 of shaft encoder 20. 
Once this shaft encoder is mechanically secured in this testing fixture 
then the electrical connection is made to the shaft encoder via connector 
27. In accordance with the preferred embodiment of the present invention, 
the testing apparatus 100 includes a plurality of cables 420. Each cable 
has a connector 423 adapted for connection to the connector 27 of a 
particular type of rotary shaft encoder. In addition, each cable 420 
includes a similar connector 425 adapted to connect to the single 
connector 245 employed in a testing apparatus 100. By this expedient, the 
testing apparatus 100 is made capable of connection to a plurality of 
differing types of rotary shaft encoders by merely selecting the 
appropriate cable 420 having the proper connector 423 for connection to 
the connector 27 of that type of shaft encoder. It should be noted that 
the connectors 27 of shaft encoder 20 may have fewer connections than the 
total number of selection devices 140 employed in testing apparatus 100. 
It is essential that testing apparatus 100 include a sufficient number of 
selection devices 140 in order to provide the proper signal or load to 
each wire of the type of rotary shaft encoder having the most wires. In 
accordance with the preferred embodiment, ten selection devices 140 are 
provided in the testing apparatus 100. 
After connection of cable 420, selection devices 140 are set. For each 
selection device 140 which is connected to a wire of the rotary shaft 
encoder, multiple position switch 141 must be switched to the proper 
position. The user would typically consult a table which indicates the 
connections required for each wire of the particular type of rotary shaft 
encoder currently being tested. This table would also typically indicate 
the particular selection device 140 to which that signal line is 
connected. By consulting this table, the user of testing apparatus 100 is 
able to select the position of multiple position switch 141 in order to 
apply the appropriate signal or load to the corresponding wire of rotary 
shaft encoder 20. In particular, it is contemplated that one or more 
direct current supply voltages must be connected to the rotary shaft 
encoder 20. It is also contemplated that the output lines of the rotary 
shaft encoder 20 will be connected to one of the plurality of load 
resistors connected to the corresponding multiple position switch 141. The 
particular load resistor employed is selected with reference to the 
particular load which the rotary shaft encoder must drive when connected 
in the controlled machine. After all of the selection devices 140 have 
been set, the rotary shaft encoder 20 is connected in a circuit which 
simulates the circuit in the machine where it is used. This permits the 
rotary shaft encoder 20 to be tested under the same conditions as it is 
used. 
Next an oscilloscope or other monitoring apparatus is connected to the 
appropriate jacks 149 on selection devices 140. It will typically be the 
desire of the person performing the test to monitor the output signals of 
the rotary shaft encoder. This can be performed by connecting the input 
probes of the oscilloscope or other monitoring apparatus to the jacks 149 
corresponding to the selection device 140 connected to the appropriate 
line from rotary shaft encoder 20. This selection is made based upon the 
table of correspondence between the particular lines of rotary shaft 
encoder 20, their function and the particular selection device 140. 
Once these connections are made the apparatus is ready to begin testing the 
rotary shaft encoder. It is contemplated that the AC line switch 105 will 
not be turned on until these connections are made. This is in order to 
prevent the application of inappropriate voltages to the lines of rotary 
shaft encoder 20. For example, if the 24-volt DC from fourth power supply 
127 is coupled to a low voltage output line, then it is very possible that 
the rotary shaft encoder will be damaged by the tester. This possibility 
can be eliminated by insuring that AC line switch 105 remains off until 
all of the selection devices 140 are properly set. 
The shaft encoder is next rotated in a desired direction and speed by 
proper adjustment of direction switch 111 and speed control potentiometer 
113 connected to motor controller 110. Under the appropriate manual 
inputs, motor controller 110 controls motor 115 to turn shafts 23 of the 
rotary shaft encoder 20. Testing the rotary shaft encoder 23 will 
typically involve controlling it in both clockwise and counterclockwise 
direction and at varying speeds. The operator can then monitor the outputs 
of the rotary shaft encoder via the appropriate jack 149 to determine 
whether or not the rotary shaft encoder 20 is generating the proper 
signals. Once the test has been completed then rotary shaft encoder 20 is 
removed from the testing fixture by reversing the steps previously 
described. 
FIG. 2 illustrates a perspective view of the testing apparatus 100 embodied 
in a suitcase in accordance with a preferred embodiment of the present 
invention. The apparatus illustrated in FIG. 2 differs from the schematic 
diagram of FIG. 1 in that FIG. 2 illustrates an oscilloscope 290 not shown 
in FIG. 1. 
In accordance with the preferred embodiment of the present invention the 
testing apparatus 100 is formed in a suitcase composed of upper shell 210 
and lower shell 220. Upper shell 220 includes latches 215 which mate with 
latches 225 in lower shell 220, enabling the suitcase to be secured when 
shut. Upper shell 210 and lower shell 220 are connected via hinges 230 
which permit the top to be opened for use. Lower shell 220 also includes 
handle 227 which permits transportation of the testing apparatus 100 to 
the location where it is employed. The suitcase includes a lock 900 so 
that the testing apparatus 100 may be secured from unauthorized access and 
use. 
Mounted within lower shell 220 and approximately flush with the top of 
lower shell 220 is a mounting plate 240 upon which many of the components 
of the testing apparatus 100 are mounted. As illustrated in FIG. 2 these 
include AC line switch 105, direction control switch 111, speed control 
potentiometer 113, voltmeter 130, voltmeter source selection switch 135, 
the plurality of multiposition selection switches 141 with their 
corresponding jacks 149, and connector 245 which connects to the various 
selection devices 140. FIG. 2 also illustrates further electrical controls 
which were not illustrated in the schematic diagram of FIG. 1. In 
accordance with the alternative embodiment illustrated in FIG. 2, 
oscilloscope selection switches 291 and 293 are provided on mounting plate 
240. Their use and electrical connection will be further described below 
in conjunction with FIG. 3. 
FIG. 2 further illustrates the test fixture used to secure the rotary shaft 
encoder in proper alignment with the shaft 116 of motor 115. This fixture 
includes a plate 250 having central aperture 255. Connecting to central 
aperture 255 are a set of spaced channels each of which includes a 
mounting clip 260. In a manner that will be more fully described below, 
mounting clips 260 are employed to secure rotary shaft encoder 20 to the 
fixture for testing. Plate 250 is connected to mounting plate 240 via a 
plurality of screw shafts 270. Screw shafts 270 can be rotated to move the 
plate 250 up or down. This provides adjustment of the height of rotary 
shaft encoder 20 relative to the shaft coupling device 117 of motor 115. 
This provides proper mating of the torque developed by motor 115 to the 
shaft 23 of rotary shaft encoder 20. 
The apparatus illustrated in FIG. 2 differs from the schematic diagram of 
FIG. 1 in that this apparatus includes an oscilloscope 290. Oscilloscope 
290 is mounted on plate 280 which is disposed in upper shell 210 and 
substantially parallel to the top of upper shell 210. Note that plate 280 
does not cover the entire upper shell 210. On the contrary, plate 280 
leaves a space where the plate 250 and the accompanying screw posts 270 
may be lodged when the suitcase is closed. Oscilloscope 290 is connected 
to the main unit mounted on mounting panel 240 via three lines 281, 283 
and 286 disposed between the lower shell 220 and the upper shell 210. Line 
281 is employed to supply AC electric power to oscilloscope 290. Lines 282 
and 286 are connected to supply the input signals to respective inputs of 
oscilloscope 290. In accordance with the embodiment illustrated in FIG. 2, 
oscilloscope 290 is of the dual trace type. 
FIG. 3 is a schematic diagram illustrating the operation of oscilloscope 
selection switches 291 and 293. The oscilloscope selection switches 291 
and 293 are essentially identical switches which are of the multiple 
position single pole type. Each is connected to the plurality of selection 
devices 140 in the same manner as the connection of jack 149. Oscilloscope 
selection switch 291 is connected to line 282 and hence to a first input 
of oscilloscope 290. Likewise, oscilloscope selection switch 293 is 
connected to line 286 forming a second input to oscilloscope 290. During 
use, oscilloscope selection switches 291 and 293 are switched to the 
appropriate selection devices 140 corresponding to the connections from 
rotary shaft encoder 20 to be monitored. Accordingly, oscilloscope 290 
provides an indication of the particular signal appearing on the selected 
line. 
FIG. 4 is a cutaway view of the details of the test mounting fixture in 
accordance with the preferred embodiment of the present invention. As 
illustrated in FIG. 4, cable 420 connects at one end via connector 423 to 
connector 27 of the shaft encoder 20 and at the other end via connector 
425 to connector 245 mounted on mounting plate 240. This provides the 
electrical connection between rotary shaft encoder 20 and the selection 
devices 140. Rotary shaft encoder 20 is secured to test fixture plate 250 
via mounting clips 260. The shaft 23 of rotary shaft encoder 20 is 
extended through central aperture 255 in test fixture plate 250. The 
mounting clips 260 are then pushed up against the body of the rotary shaft 
encoder 220 and secured there. This is provided by tightening of screws 
261 which form a part of mounting clips 260. rotary shaft encoder 20 is 
then secured to plate 250. 
The height of plate 250 is then adjusted by rotation of the four screw 
posts 270. This rotation is facilitated by handle 275 on one of the screw 
posts 270. The screw posts 270 are ganged together underneath mounting 
plate 240. Each of these screw posts 270 includes a gear 410 which is 
connected through a common chain 415 to all of the screw posts. Rotation 
of one of the screw posts then causes rotation of all. This rotation 
causes plate 250 to be moved up or down depending upon the direction of 
rotation. Plate 250 is initially moved up to position where shaft 23 is 
beyond the shaft coupling device 117. Once the rotary shaft encoder 20 is 
secured to plate 250 then plate 250 is lowered until shaft 23 mates with 
shaft coupling device 117. FIG. 4 illustrates set screw 118 which is used 
to secure shaft 23 within shaft fixture 117. Once the shaft 23 has 
properly mated with shaft coupling fixture 117 then set screw 118 is 
secured in order to transmit the torque from shaft 116 of motor 115 to the 
shaft 23 of rotary shaft encoder 20.