Parts sorting systems

A system for sorting parts wherein a part to be sorted is irradiated with wave energy of a single frequency (or very narrow band of frequencies) which interacts with the part. Wave energy emanating from the part is sensed at many spatially separated places to generate an electric signal representative of a characteristic of the amplitude and phase of the detected wave energy at each place. The electric signal so generated is compared with a pre-established signal and any differences therebetween are determined to establish whether the part is within acceptable limits in terms of geometric characteristics, e.g., size, material characteristics and orientation. The part is then acted upon on the basis of the comparison.

BACKGROUND OF THE INVENTION 
The present invention relates to parts sorting systems. 
Attention is called to U.S. Pat. Nos. 4,095,475; 4,200,921; and 4,287,769 
to the inventor B. Shawn Buckley herein. 
In batch processing of the nature discussed herein, batches of parts from 
50 to perhaps 1000 are processed at one time. Batch processing, which 
represents 75% of the dollar value of parts manufacturing, is economically 
appropriate for those parts which are made in volumes of less than a 
million parts per year. However, batch processing is a labor intensive 
approach that results in high cost per unit relative to automated parts 
manufacturing or hard automation. 
In hard automation, the volume of parts processed is high enough that a 
machine can be built and dedicated to the manufacture of a particular 
part. Usually a million or more parts per year are needed to justify 
economically such a dedicated machine. It is called hard automation 
because "hard" tooling is needed to manufacture a particular part. If the 
design of a part should change, often another machine must be built to 
automate its manufacture, even for relatively minor changes in the part's 
design. Despite the drawback of requiring special-purpose machines for 
each part design, hard automation remains the most economical method of 
manufacturing when millions of a part are to be made. 
"Soft" automation is an attempt to apply hard automation principles to 
batch processing: it replaces the "hard" tooling with electronic 
computers. The computers can be quickly reprogrammed to manufacture a part 
of a different design without performing the task manually or redesigning 
the machine that makes the part. In metal cutting, "soft" automation 
incorporates numerically controlled (NC) lathes and milling machines; in 
warehousing, it incorporates automatic retrieval systems; in paint 
spraying and spot welding it incorporates industrial robots; in factory 
automation, it incorporates programmable controllers. 
However, in parts handling systems the versatility of "soft" automation has 
not been realized. True, industrial robots can be programmed to manipulate 
a part in enormously complicated ways once given a part to manipulate. 
But, unfortunately, it has no versatile way of obtaining the parts in the 
first place. Each robot comes equipped with custom-tooled parts feeders, 
whose cost is typically three to five times the cost of the robot itself. 
The parts feeders, the dominant cost in a robot parts handling system, 
must be custom designed and installed for each part a robot manipulates. 
Thus the robot becomes a mere accessory to what is essentially a hard 
automation system. While the robot is versatile enough to handle a variety 
of parts, the system to which it is coupled is not. 
Vision systems represent an attempt by "soft" automation experts to couple 
the robot to the parts that it must handle. Unfortunately, vision systems 
are expensive compared to manual methods. Although they hold the promise 
of enabling a robot to feed its own parts, presently they are not a 
practical way to do so. A versatile low-cost method of feeding parts to 
robots is required before "soft" automation comes to parts handling in 
manufacturing. 
Feeding parts to a robot, or for that matter a dedicated automation 
machine, requires that the parts be properly oriented. Parts usually come 
in baskets or bins, oriented randomly. The task of a parts feeder is to 
ensure that the parts are presented to a robot in the same way for each 
part. For example, the cap of a ball point pen must be presented to a 
robot in a particular orientation for the subsequent mating to the body to 
occur properly. 
In addition to orienting parts for soft or hard automation, inspection of 
the parts is also important. In hard automation, defective subcomponents 
can double the cost of assembling a typical component. The difficulty is 
downtime: defective parts jam a machine and require operator time to fix 
the jam. Stopping production to unjam a machine reduces the production 
rate significantly--enough to justify the highest quality parts. But high 
quality parts themselves are expensive so a compromise is reached between 
the increased cost of high quality parts and the increased cost of 
unjamming machines. 
If low-quality parts were sorted prior to assembly by a dedicated 
automation machine, significant saving would result. Downtime due to jams 
would be eliminated, production rates would increase and manufacturing 
costs would be reduced. Robots used in manufacturing of parts could also 
benefit from using pre-sorted parts: jams in robot-based systems can often 
result in damage to the robots. 
Accordingly, it is an objective of this invention to provide a parts 
orienting device which automatically feeds similar objects to an 
inspection region, detects their orientation through various sensors, and 
manipulates the objects to ensure that objects leaving the orienting 
device have only the desired orientation. 
Another objective of the invention is a parts-sorting device which 
automatically feeds similar objects to an inspection region, detects the 
shape of the objects through various sensors and manipulates the objects 
to ensure the objects leaving the sorting device have only the desired 
shape or other sensed characteristics. 
These and still further objectives are addressed hereinafter. 
The foregoing objectives are achieved, generally, in an apparatus for 
sorting parts for the purpose of interfacing with an industrial robot or 
the like or for presenting those parts to a production machine or the 
like. A feeder transports a part into a sensing region where it is 
subjected to wave energy of a single or narrow-frequency band. Reflected 
or other wave energy resulting from the impinging wave energy is sensed at 
a multiplicity of places to provide signals from which amplitude 
information and phase information of the received wave energy can be 
derived with respect to each place. An analyzer extracts from the 
amplitude information and the phase information intelligence with respect 
to a geometry parameter and/or electromagnetic parameter the part, which, 
in turn, is used to sort the part. It will be appreciated that the 
geometry or electromagnetic parameters includes position data as well as 
shape data with respect to the irradiated part.

The present invention, schematically as shown in FIG. 1, consists of five 
basic elements: a parts storage device 1; a parts feeder 2; a wave energy 
emitter and sensor 4; a processor/analyzer 200; and sorting mechanisms. 
The parts storage device 1 that holds a number of the objects 8 (also 
identified as 8A, 8B . . . ) which are to be sorted or oriented. An 
electrically actuated gate 11 on the hopper 1 feeds parts 8 into the 
feeder 2. The feeder 2 shown is a bowl feeder, known for its ability to 
feed a variety of parts 8 with little, if any, modification of the feeder 
for a new shape of part 8. The hopper gate 11 is set to feed parts from 
the hopper 1 (when the feeder 2 runs out of parts 8) via a fill paddle, 
not shown to simplify the figure. Such an arrangement of feeder 2 and 
hopper 1 with automatic fill between the two is standard in the industry. 
(Another variation of feeder 2 is a belt feeder with its attendant storage 
hopper similar to the hopper 1.) 
The purpose of the feeder 2 is to move the parts to a transfer mechanism 3 
to convey the parts 8 under a sensing mechanism 4 (the sensing mechanism 4 
both transmits and receives wave energy). In general, the parts 8 must be 
fed one at a time to the sensors 4; so often an escapement 12 is 
necessary. An escapement allows one object 8 (e.g., 8A or 8B . . . ) to 
move to the sensing region 13. In some cases, the feeder 2 itself acts to 
only allow one part 8 at a time to move the sensing regions by a process 
called singulation. In other situations, the transfer mechanism 3, shown 
in FIG. 1 as a belt, can act to separate the parts 8 by accelerating the 
parts 8 as they move to the top of the feeder 2. If the parts 8 move along 
the transfer mechanism 3 faster than they arrive from the feeder 2, the 
tendency will be to separate the parts 8 one from another. (Other ways to 
separate the parts 8 so they arrive one at a time include rotating brushes 
and air jets which accelerate the parts thereby separating them, much as 
does the belt described.) 
When individual parts (e.g., the part 8A) arrive at the sensing region 13, 
the sensors 4 transmits continuous acoustic and/or electromagnetic wave 
energy of a single (i.e., narrow band) frequency into the sensing region 
where the wave energy interacts with the part 8A and is reflected to the 
sensors 4. The sensors 4, as later discussed, consists of a multiplicity 
of sensors that receive the wave energy after interaction with the part 
and sense the shape of the part or its orientation by means of acoustic 
and/or electromagnetic wave information, as described in the 
above-mentioned Buckley patents. The sensing mechanism is discussed later 
with reference to the prior Buckley patents; analysis is effected in the 
processor/analyzer 200 which may, in part, be a microcomputer or the like, 
to provide sorting signals. 
Once the shape or orientation of the object 8A has been determined, the 
part proceeds to a rejection gate 5 which may be actuated by signals from 
the unit 200. If the part 8A is found to have the proper shape or 
orientation, it proceeds to a parts presentation point via a transfer 
mechanism 14 (shown in FIG. 1 as a belt conveyor) where the part is 
labeled 8B. In robot operations, the part 8B is held in its proper 
orientation by a stop 15 for pickup by a robot, not shown. In some other 
robot operations, parts 8A are taken from the parts presentation point 
without the interaction of the rejection gate 5; the robot simply changes 
its actions based on the shape or orientation. In automated manufacturing 
operation, the transfer mechanism 14 would deliver the properly shaped and 
oriented part 8B directly to the dedicated automation machine, not shown. 
In parts sorting operations, the transfer mechanism 14 can simply deliver 
the parts 8B of the correct shape to a bin 7 where correct parts are 
designated 8C. 
Meanwhile, parts of incorrect shape or orientation (marked 8D) are rejected 
from the transfer belt 14 by the gate 5. In a parts sorting operation, the 
parts 8D can be simply stored in a bin 6. In robotics or hard automation 
applications where proper part orientation is required, the parts 8D which 
are correct parts (though improperly oriented) are transferred to other 
transfer mechanisms 9 and 10 so that parts of correct shape but incorrect 
orientation may be returned to the feeder 2. Once the parts 8 are returned 
to the feeder they are randomly oriented so that they may be subsequently 
fed to the parts feeder mechanism 14, should the new orientation be 
correct. 
In FIG. 1, the various mechanisms have been separated to elucidate their 
functions. In an actual sorting or orienting device, some of these 
mechanisms can be combined to give the appropriate functions. For example, 
the transfer mechanisms 3, 9, 10, and 14 in FIG. 1 are more easily 
designed as gravity chutes which take a part from the top of the feeder 
and divert it either to a parts presentation stop or back to the feeder as 
shown in FIG. 2. 
Parts 21 in FIG. 2, travel to the top of a vibratory bowl feeder 20 and 
then slide down a gravity chute 22 to an inspection region below a sensing 
mechanism 23. A computer (not shown) analyzes the sensor signals from the 
sensing mechanism 23 and actuates a part rejection mechanism 25. In this 
case, an air jet is a method by which a defective part 21D or an 
improperly oriented part is diverted from a gravity chute 24 back into the 
bowl feeder 20. Such parts 21D typically re-orient themselves on a 
successive journey up the spiral inner track of the feeder 20. A hole 26 
through the side of feeder 20 allows re-introduction of defective or 
misoriented parts 21D back into the feeder 20. In some situations, 
defective parts 21D are distinguished from misoriented parts 21D and 
subsequently fed to a reject parts bin via a diverting mechanism such as 
the air jet 25. 
Another variation of the same parts feeding and orienting apparatus is 
shown at 30 in FIG. 3 where parts are marked 35, 35A-35D. In FIG. 3 a belt 
feeder, similar to one sold industrially by the Page-Wilson Corporation, 
of Bridgeport, Connecticut, combines the transfer mechanism 3, 9, 10 and 
14 of FIG. 1 but without an intermediate feeder 2. The feeding/orienting 
system 30 has an automated parts hopper (not shown for clarity) which 
maintains an adequate supply of the parts 35 on a main belt 31. 
Essentially the feeder/orienting system has two belts 31 and 32 which 
circulate parts 35 within the confines of a fence 37. The main belt 31 is 
inclined as will be discussed shortly. Parts 35 travel up the main belt 31 
and onto the secondary belt 32. 
A sensor mechanism 33 senses the shape or orientation of the parts 35. 
Parts of the wrong orientation or defective parts 35B are diverted back 
onto the main belt 31. Shown here is an air jet 34B which is actuated by a 
computer (not shown) when the sensor signals from the sensing mechanism 33 
indicates the improper orientation of a part 35B. Diverted parts 35B 
tumble over a step 36 and re-orient themselves such that on subsequent 
passes past the sensing mechanism 33 they have a possibility of passing 
onto the gravity chute 38. The chute 38 can be a parts presentation chute 
for a robot so correctly oriented parts 35C can be grasped by a robot. 
Alternatively the chute can feed properly oriented parts 35C directly to a 
hard automation manufacturing machine (not shown). 
Other variations of the parts feeding and orienting system 30 can improve 
its usefulness. A diverting mechanism, in this case an air jet 34A, can 
insure that only a single part 35 at a time enters the sensing region 
below the sensing mechanism 33. Thus, if parts 35 travel down the 
secondary belt 32 too fast for proper sensing, the sensing mechanism 33, 
via the computer, can command the air jet 34A to actuate until sensing is 
complete. 
Diverting mechanism 34C, in this case an air jet, may be used to reject 
defective parts 35. If a defective part 35D is sensed by the sensing 
mechanism 33, the air jet 34C is actuated by the computer to divert the 
defective part 35D into a reject part bin 39. 
Another variation of the present invention is a parts sorter 40, as shown 
in FIG. 4, in the form of a bowl. Here a parts feeder 41 brings parts 42 
to the top of the bowl. An accompanying parts hopper, such as the hopper 1 
in FIG. 1, can be added to insure an adequate supply of parts 42 arriving 
at the top of the bowl. An escapement or singulation mechanism 43 allows 
only one part 42A at a time to slide down a chute 45 and beneath a sensing 
mechanism 47. The computer (not shown) analyzes the shape of the part 42A 
and actuates gates 44A and 44B depending on the analysis of the sensor 
signals from the sensing mechanism 47. Parts 42B of one shape are diverted 
by gates 44A and 44B into one bin 46 while parts 42C and 42D of other 
shapes are diverted into other bins 46. 
The shapes can be correct parts and incorrect parts, or the parts may be 
sorted according to other criteria. For example, the parts 42B can be 
coins of one denomination while parts 42C and 42D can be coins of other 
denominations. On the other hand, the parts 42B can be threaded fasteners 
such as screws with threads while the parts 42C can be the same screws but 
without threads. In either case, the parts are sorted in various 
categories on the basis of shape or electromagnetic characteristics. 
It will be noted that the system 40 is primarily a parts sorter rather than 
a parts orienter. Usually parts of incorrect orientation must be tumbled 
and recycled to some sensing mechanism as are the parts 8D in FIG. 1, the 
parts 21D in FIG. 2 and the parts 35D in FIG. 3. However, in the system 
40, no mechanism exists for transporting correct parts, but of the wrong 
orientation, back to the bowl 41. If required, cogged belts (such as the 
belt 10 in FIG. 1) may be used for those parts orienting applications 
where correct but misoriented parts must be returned to the parts feeder. 
The sensing mechanisms in FIG. 1-4 require that the parts being sensed are 
not moving for the highest accuracy measurement of the part's shape. In 
these applications a part-stop mechanism can be positioned to stop the 
parts moving beneath the sensing mechanism. FIGS. 5A and 5B show how such 
a mechanism is implemented for gravity chutes and for belt transfer. FIG. 
5A shows a part 51 which has slid down a gravity chute 50 (such as the 
chute 22 in FIG. 2 or the chute 45 in in FIG. 4). A solenoid 53 attached 
by a bracket 56 is spring-loaded by a spring 55 to extend a gate 54 into 
the path of the part 51, when actuated by an electrical signal on input 
wire 57 from a computer (not shown). The gate 54 has two positions: 
extended 54B and retracted 54A. When the part is stopped, the sensing by a 
sensing mechanism 52 is much more accurate. 
FIG. 5B illustrates a similar solenoid actuating gate mechanism for a belt 
transport mechanism (such as the belt 3 in FIG. 1 or the belt 32 in FIG. 
3). A part 61 moving on a belt 60 adjacent to a fence 68 is stopped in the 
sensing region of a sensing mechanism (not shown) by a solenoid 63 driving 
a gate 64 into its extended position 64B or its retracted position 64A; a 
spring 65 returns the gate to its retracted position while bracket 66 
positions the solenoid 63 for proper operation. 
Gates such as 54 and 64 can be pneumatically driven rather than 
electrically driven by devices common in the hard automation industry. 
Electrically driven gates are used for illustration because they are most 
commonly connected to computers through the use of relays. Similar 
solenoid-driven gates may be used for escapement or singulation mechanisms 
such as mechanism 12 in FIG. 1, mechanism 34A in FIG. 3 or mechanism 43 in 
FIG. 4. In any of these mechanisms, the computer actuates the gates only 
so long as to let a single part continue past the gate. 
For shape measurement determination of somewhat lower accuracy, a detector 
is often required to insure that the sensing of the part 51 (FIG. 5A) 
occurs when the part is in the proper position relative to the sensing 
mechanism 52. In these applications a part presence detector replaces the 
part-stopping mechanisms in FIGS. 5A and 5B. Parts presence detectors 
include microswitches or proximity detectors which the part 51 actuates; 
such detectors are available from many suppliers as are optical trips 
wherein the part 51 breaks a beam of light. The latter method was used by 
Mellen ("Inspection of Moving Parts via Acoustic Phase Monitoring," M. S. 
Thesis, Mechanical Engineering Dept., M.I.T., June 1979, D. B. Mellen) in 
evaluating the accuracy of acoustic sensors on moving parts. 
The sensing mechanism itself is the critical component of the parts sorting 
orienting systems shown in FIG. 1 through FIG. 4. The sensing mechanism is 
composed of an array of sensors which use either acoustic or 
electromagnetic wave variations as discussed in the Buckley U.S. Pat. Nos. 
4,095,474 and 4,200,921. A brief summary of those sensors will now be 
discussed. 
Acoustic sensors are composed of transmitter-receiver transducers such that 
sound waves are transmitted by the transmitter, interact with the part and 
are picked up by the receivers. FIG. 6A shows an array 70 composed of 
transmitter 71 and receivers 72 used to detect the shape of a part 74. 
Electrical signals input to transmitter 71 via contacts 75 are transduced 
into acoustic wave energy 76 which interacts with the part 74. The 
variations in wave energy 76 are received by receivers 72 whose output 
signal is available on contacts 73. 
Electromagnetic sensors are shown in FIG. 6B (inductive sensors) and FIG. 
6C (capacitive sensors). While sensors of this sort are quite common in 
such devices as proximity sensors, their use as a method of detecting a 
part's shape as part of a multi-element array of sensors using continuous 
wave energy and interpreted in the manner herein described is wholly new 
and innovative. A brief discussion of useful sensors and how they may be 
used in conjunction with the acoustic transducers just described follows. 
FIG. 6B shows an array 80 of inductive sensors 82 which are simply coils 
of wire. Electromagnetic wave energy 86 emanating from the sensors 82 
interacts with a part 84. Electrical output signals from the sensors 82 is 
available on contacts 83. Inductive sensors such as those described are 
useful in determining the shape of a part 84 as well as certain magnetic 
properties of the part such as hardness and alloy. 
FIG. 6C shows capacitive sensors 92 fixed to an array 90. The sensors 92 
are simply conducting plates which can generate electromagnetic waves 96 
which interact with a part 94. The interaction can be detected via 
electrical contacts 93 for interpretation by the computer. Capacitive 
sensors such as those described can detect other properties of the part 94 
such as dielectric constant of certain plastics and the water content of 
paper products. 
The electrical output signals on contacts 73 of the acoustic sensors 72 of 
FIG. 6A are sinusoidal signals whose amplitude and phase vary according to 
the shape of the part 74. These signals are subject to the details of the 
transduction method employed. In general, transducers 71 and 72 may 
operate by several well-known principles: electric diaphragms coupled to 
sensitive amplifiers, piezoceramic crystals coupled to sound-collecting 
diaphragms, "condenser" transducers coupled to a metal or plastic 
diaphragm and "voice-coil" transducers which couple coils embedded in a 
diaphragm in a driver coil close by. 
For the electrical output of electromagnetic transducers (such as the 
sensors 82 and 92) to produce a similar phase and amplitude signal, 
several well known principles can be employed. In the following 
descriptions of these circuits, the generalized impedance Z will be used 
to represent either an inductor or a capacitor. FIG. 7A shows a 
self-impedance circuit 100 in which an impedance 101 is varied by its 
interaction through electromagnetic wave energy 106 with a part 105. The 
wave energy 106 is produced by a continuous wave electrical voltage source 
103 driving current through resistor 102 and impedance 101. The voltage 
signal across terminals 104 is characterized by its amplitude and phase 
which is subsequently interpreted by a computer 200. 
Typically the resistance 102 would be chosen such that the operating 
frequency of the circuit 100 is near the circuit's "break frequency" to 
maximize the change in amplitude and phase with changes in the shape of 
object 105. Other circuit elements can replace the resistor 102. For 
example, if a capacitor C, coupled with a resistor R, is substituted for 
the resistor 102 and the impedance 101 is an inductor L, tuned to the 
resonance of the LRC circuit, the amplitude and phase characteristics 
measured at the terminals 104 become quite sensitive to changes in the 
shape of part 105. 
The circuit 100 in FIG. 7A is termed "self-impedance" because the sensor 
101 both sends and receives electromagnetic wave energy. FIG. 7B is a 
circuit which is termed "transimpedance" because an impedance element 111 
sends electromagnetic wave energy 116 and other impedances 112 receive the 
wave energy. An electrical voltage or current source of continuous waves 
113 causes the impedance 111 to emanate wave energy 116 which interacts 
with object 115 to change the amplitude and phase signals output on 
terminals 114. For example, if the impedances 111 and 112 are coils, the 
transimpedence between the coils will vary depending on the shape of the 
object 115: the changes can be detected through amplitude and phase 
differences measured at the output terminals 114. 
A third technique for detecting shape and other changes of a part is shown 
in a bridge circuit 120 in FIG. 7C. A continuous voltage or current source 
123 drives the bridge composed of impedances 121, 122, 127 and 128. The 
bridge is balanced in the usual manner with impedances 121 and 122 chosen 
to be nearly equal to the impedances 127 and 128. Any change in the 
impedance 121 due to interaction with a part 125 through electromagnetic 
wave energy 126, causes a change in the amplitude and phase voltage 
signals on contacts 124. 
It will be noted that all sensors, whether acoustic or electromagnetic, 
produce changes in the amplitude and phase of electrical signals to which 
they are connected. The sensors either produce wave energy or they receive 
wave energy which interacts with a part to convey information about the 
part. Usually the information is shape information but it can also include 
position and orientation information as well as certain other properties 
of the part. While each array shown has included only one type of sensor, 
in general any array can include several types of sensors all of which are 
interpreted in the same manner by the computer 200. Moreover, the sensors 
have been shown as simple linear arrays. In general, the sensors are 
deployed in a manner which best suits the class of parts which they are 
sensing. For example, inductive sensors for cylindrical parts have 
inductors through which the parts pass; acoustic sensors deployed in 
"phased arrays" become sensitive to specific regions of a part. 
Now follows a brief discussion of the technique by which the computer 
interprets the amplitude and phase information from the various sensors. 
More detail on the method can be found in Buckley U.S. Pat. Nos. 4,095,474 
and 4,200,921. FIG. 8 shows a parts sorting system 130 which details the 
function of the computer labeled 144. It will be noted that the system 130 
is only a partial sub-system of the complete parts sorting and orienting 
mechanism of FIG. 1. 
An object or a part 132A or 132B is transported down a transport mechanism 
such as a chute 131 from the ready position occupied by the part 132B. 
Solenoid gate mechanisms 146A and 146B, on signals 145 from the computer 
144, ensures that only one part 132A is in the sensing region beneath the 
sensor array 148. In this example, the sensing array shown at 148 has a 
transmitting sensor 133 driven by the computer 144. 
As discussed previously herein, the wave energy from the transmitting 
sensor (or transducer) 133 interacts with the part 132A and changes the 
amplitudes and phases of the continuous wave signals detected by the 
receiving sensors 134. These signals are fed to a multiplexor (MUX) 137 by 
connections 136, where one of the signals is chosen by the computer 144 to 
be analyzed. The connection 147 is a bus by which the computer 144 signals 
the multiplexor 137 which of the signals on connnections 136 is chosen. 
The chosen sinusoidal signal from the sensors 134 is fed via a connection 
138 to an analog amplifier and filter 139 which amplifies or attenuates 
the signal (as required) and reduces noise at frequencies other than the 
sinusoidal operating frequency of the transmitted wave energy. 
Next, the signal is converted to a digital value in a analog to digital 
converter ADC 140. The filtered sinusoidal signal is sampled at various 
time intervals as determined by a clock signal fed to the ADC 140 by the 
computer 144 via connection 142. The sampled digital values are sent to a 
digital filter 141 by a bus 149 where they are further filtered to remove 
noise at frequencies other than the transmitted wave energy frequency. 
Lastly, the filtered data is transmitted to the computer 144 via bus 143 
for analysis. Analysis of the filtered data first requires that the data 
be converted to amplitude and phase information of the received wave 
energy for the chosen sensor 134. A Fourier transform algorithm, available 
in the literature, readily converts the digital values to amplitude and 
phase information. Note that in high performance systems which must 
operate at higher measurement rates, some of the elements shown in system 
130 may be duplicated to allow their tasks to be done in parallel rather 
than serially. For example, a system which had two each MUX's 137 analog 
filters 139, ADC's 140 and digital filters 141 could make measurements 
twice as fast as system 130. 
The computer 144 orchestrates the data gathering from sensors 134. First it 
transmits the operating frequency to the transmitter 133; it then directs 
one after another of the received sensor signals input from the MUX 137 to 
the analog amplifier and filter 139. The computer 144 also determines the 
timing and the duration of the data sampling in the ADC 140 and, further, 
receives and analyzes the amplitude and phase information from the digital 
filter 141. As each sensor signal, in turn, is processed, the computer 
144, also stores the amplitude and phase information from previously 
processed sensor signals until all sensors 134 in the array 148 have been 
processed. 
Given the phase and amplitude information from each sensor 134, analysis 
involves calculations of the general form: 
##EQU1## 
X is the desired output g is a functional relationship 
W.sub.i is a weighting function chosen for each sensor 
f is another functional relationship 
A.sub.i is the amplitude of each sensor signal 
.theta..sub.i is the phase of each sensor signal 
N is the number of sensors 
For example, in determining the diameter of a part 132A, the desired output 
X is the diameter. By choosing the weights W.sub.i to be proportional to 
each sensor's phase difference between a master part (of diameter D" and 
with phase .theta.".sub.i) and another part (whose diameter is D' and with 
phase .theta.'.sub.i) the relationship simplifies to: 
##EQU2## 
Other relationships g and f are appropriate for other desired outputs such 
as determining one part from another or one orientation from another. 
While the foregoing descriptions give ways to orient and sort parts, 
certain other apparatus and methods can improve the general resolution of 
the measurements, especially acoustic measurements. 
The improved resolution techniques fall into three categories: temperature 
control of the medium, moving the medium and temperature control of the 
sensors. FIG. 9 shows a typical application where all three of the 
techniques are used. A parts sorter or orienting system 150 has a part 151 
held in a chute 152 (viewed end-on). Wave energy is transmitted by a 
transmitter 153, interacts with the part 151 and is received by receivers 
154 in an array 155, as has previously been discussed. The medium 156 
through which the wave energy is transmitted is both moving and 
temperature-controlled. 
The moving medium 156 is propelled by a fan 157 which forces the medium 
past the object 151. In practice, simply maintaining a gentle flow of the 
medium 156 can improve long-term phase and amplitude resolution by a 
factor of five or more. The present inventors believe that the moving 
medium 156 ensures that the average temperature of the medium 156 varies 
less quickly than if the medium is still. Since acoustic measurements (and 
to a lesser extent electromagnetic measurements) are influenced by the 
medium's temperature, temperature stability gives better phase measurement 
resolution. 
In addition to simply moving the medium, even better long term phase 
measurements result if the medium's temperature is held fixed. In FIG. 9, 
a heating element 158 heats the medium 156 before flowing past object 151. 
A temperature sensor 159 detects the medium's temperature and controls the 
energy to the heating element 158 by a controller 160. Mixers and baffles 
161 ensure that the medium 156 is thermally mixed before flowing past the 
object 151. By controlling the temperature of the medium 156, compensation 
for the change in the wavelength of acoustic wave energy (as discussed in 
Buckley U.S. Pat. No. 4,287,769) is not required. It will be noted that it 
is the temperature of the medium 156 which must be controlled, not that of 
object 151. 
Although temperature changes of the medium are the principal reason for 
errors in measuring amplitude and phase (especially for acoustic wave 
energy), other medium changes can affect measurement resolution. For 
example, in certain capacitance sensors, the humidity of the medium can 
produce errors in the shape or orientation paramenters measured. Humidity 
control of the medium is one way of reducing these errors; humidity 
controls are standard industrial hardware available from several 
suppliers. 
Another way of improving the amplitude and phase measurement of acoustic 
and electromagnetic sensors 153 and 154 is by holding fixed the 
temperature of the array 155 along with its sensors and 154. The sensors 
153 and 154 are mounted on a heat conducting block, such as aluminum, with 
good thermal contact between sensors and block. A temperature sensor 162 
senses the block's temperature and controls the energy to a heating 
element 163 via a temperature controller 164. The sensors 153 and 154 are 
held at a temperature higher than would be encountered in the field such 
that heat must always be added to the array 155 to hold its temperature 
fixed. By keeping the sensors 153 and 154 at a fixed temperature, drift of 
amplitude and phase measurements can be all but eliminated. Since each of 
the sensors 53 and 154 seldom has the same measurement drift with 
temperature as the other, holding the array 155 at a fixed temperature 
eliminates the cost of matched sensors. 
A last method for compensating for changes in the medium is discussed in 
Buckley U.S. Pat. No. 4,287,769. In that method, certain property changes 
of the medium cause a corresponding (and known) change in the wavelength 
of the continuous wave energy. Changing the frequency of the transmitted 
wave energy by the proper amount ensures that the phase and amplitude 
information remains constant despite property change of the medium. In the 
cases where the property changes are temperature or humidity, temperature 
or humidity sensors can determine the amount of frequency change required. 
For this and other property changes of the medium, the frequency can also 
be corrected by comparing amplitude and phase information made with no 
part in the sensing region and adjusting the frequency until no change 
appears in the phase and amplitude information. 
Further modifications of the invention herein disclosed will occur to 
persons skilled in the art and all such modifications are deemed to be 
within the scope of the invention as defined by the appended claims.