WO 9S/07772 2 ~ 7 1 9 7 9 PCT/US94/10349 .

NON-DESTRUCTIVE FIRMNESS MEASURING DEVICE

BACKGROUND OF 1~ INVENTION
1. Field of the Invention The present invention relates to a device and a means for dete Inining the fi~ ess of objects, and more particularly to a device and means for non-destructively measuring the filll.lless of objects using a fluid jet and a light beam specifically for 10 determining the filll~ess of food products.

Description of Prior Art Firmn~se j~, rPeiet~n~e to dt;rullllalion, is a key factor in determining the quality of food products. Cone mers consider fillllness as a predictor of the storing 15 ability and eating quality of fresh fruits and vegetables. Food buyers use fil ll.ness whe selecting which lot to purchase. Firmness is also a key factor for growel ~ in deri~ing on harvest dates and in sorting products at paçl~ing houses.
One of the plilll~ly functions of a fresh fruit and vegetable p~ç~ing house is to convert a highly variable incoming flow of a product into p~çL ~ee col~ )g products 20 with uniform quality. Many products continue to ripen after harvest, therefore the items packed must be firmer than desired by the end user. Thus, a critical operation at paçl~in~ houses is to remove riper items which are often the highest quality and more valuable for regional markets but would become soft and cause wholesale buyers to reject the entire shipm~nt when delivered to distant markets. Soft fruit was also the 25 most frequently reported physiological disorder recorded on USDA inspection forms for plum, peach, and ne~ e ~h~pllltll~s to the New York market between 1972 and 1985, 2171979 ~

where 40% of the ~1,;l,. . .f.. .l ~ inspected were . ~je~,led for being too soft, Ceponis, Cappellini, Wells, and T ightner~ "Disorders in plum, peach, and nec~ e ~hip.l.e..ls to the New York market, 1972-1985," Plant Disease 71(10) 947-952 (1987).
Unacceptable variations in r~l..ness frequently occur during food production, 5 m~mlf~c~lring processes, and product storage. A common approach for ~ E
variability and for ~ ing products with uniform fil.l.lless is to separate items into groups with similar filll.l-ess levels.
Presently, manual separation is the only practical method available to p~1,ing houses for firmness sorting. The sorting task is labor intensive, monotonous, and 10 inaccurate. Con~eq~lently~ there is a strong need for development of a meçh~nical device to separate objects based on fi....lless.
There are several methods of measuring firmness. One method measures firmness by des~. oy~ng the item under test. With this method, one randomly selects samples from a lot and measures them under the assumption that they . epresenl the total 15 popula~ion. The traditional measure of fruit firmness is with a pene~,ullle~el described in Magness and Taylor, "An Improved Type of Pressure Tester for Dete....inaLion of Fruit Maturity," USDA Circular 350 (1925). This device destructively measures the r..lmless of an object by d~L~ g the force necç~,y to penell~Le the object with a probe to a predetermined depth. A more recent method is ~ rlosed in Studman and Yuwana, 20 "Twist Test for Measuring Fruit Firmness," 23 J. Texture Studies 215-227 (1992). This reference plese~lLs a fi---~lless measurement method based on the moment necess~ry to rotate a blade ~tt~çh~d to a spindle after it is pushed into the fruit.
A disadvantage of destructive testing is that to achieve higher levels of reliability one must destroy greater numbers of the product, and one cannot measure the fi..nness 25 of every item going through a packing line. Furthermore, the ability for a sample to predict the condition of the lot is especially weak for fruit because weather and other variables prevent the control of processes which affect firmness. Thus, a lot will have large variations that are only partially reduced by manual sorting.
Destructive tests for fil ln.~ess continue, largely because suitable sensors are not 30 available for measuring firmness of all items in a lot. Consequently, effort has been expended on several approaches for finding a non-destructive fi---~iless method. Such WO 95107772 2 1 7 3 ~ 7 9 PCTIUS94/10349 .

methods have either required mech~nic~l contact between the product and a solid probe or measurement of a secondary property which is subsequently correlated to L~ ess.
A non-destructive ...ecl-A,-ical contact measulenlell~ is described in Mizrach and Ronen, "Mer.h~nic~l Thumb Sensor for Fruit and Vegetable Sorting," 35(1) 5 Transactions ofthe ASAE 247-250 (1992). In this reference, a ~".eçhAnic~l thumb" is used to measure force-dt;rol l"aLion. With this method, the product is dero"lled by a pin conn~cted to a pivot arm with a micro-switch. Measurement of filllllless by d~;rollllalion using two steel balls pushed against opposite sides of the fruit has been described in Mehl~h~-l, Chen, Claypool, and Fridley, "A Deroll,lt;ler for Non-Destructive Maturity 10 Detection of Pears," 24(5) Transactions ofthe ASAE 1368-1375 (1981). Dawson, "Non-destructive Firmness Testing of Kiwifruit," Programme Il~llllalion and Abstracts ofthe Second Intern~tion~l Symposium of Kiwifruit, 18 February 1991, Massey University, Palmerston North, New 7e~1~n-1 describes a non-destructive fil"",1ess tester for kiwifruit based on the displ~cçmçnt of a small mass pushed against the fruit by a 15 spring. A micro-switch intlic~tes when derollllaLion eycee~ls the present limits. A single lane L.llllless sorting m~.hine is described in Delwiche, McDonald, and Bowers, "Detel...;~ n of Peach Firmness by Analysis of Impact Forces," 30(1) Tr~n~r,tions of the ASAE 249-254 (1987). This m~.hine is used for sorting peaches and pears intohard, firm, and soft categories by analyzing the force from the fruit imp~ctin~ a plate 20 supported by force tr~n~chlc~rs. The sorting index used in this reference uses a relationship between the peak force and the time ~t;4ui~ed to reach the peak force.
Measurement of r"lllness by deroll"alion caused by an applied force is possible because the slope of a force-derollllalion curve is the mo~ ls of elasticity, or ~ r..ec~
ofthe product. A standard is available for "Colllples~ion test of food material of convex 25 shape," ASAE S368.1, inASAE Standards, 39thEdition, Am. Soc. Agr. Engrs., St.Joseph, MI (1992). Terms are defined and specifications are given for tests using parallel plates, a single plate, a spherical in~lçnter on a curved surface, and a spherical inrl~nt~r on a flat surface. A section on c~lc~ tions provides standardized methods for finding force and dt;ro,malion on bio-yield and to rupture, point of inflection, modulus 30 of deformability, and stress index. An equation relating impact force to time is provided by Zhang and Brusewitz, "Impact force model related to peach L,lllness," Trans. ofthe ~171q7q ASAE 34(2) 2094-2098 (1991). This equation relates to the force-time response ofpeaches impacting a load platform. Other rese~.,l-es have reported on measult;mt;l,~s of quantities such as co~ffi~ient of restitution and penell u~ er peak voltage (m~x;. .
deceleration).
Measurement of secondary plupel Lies is described in Perry, "A non-destructive firmness (NDF) testing unit for fruit," Trans. ofthe ASAE 20(4) 727-767 (1977). The device described in this reference measures ~llmiless using low-pressure air .ciml~lt~n~ously applied to small areas on opposite sides of pe~c.hes A lu~ steel drum has been used for se,oal~ g soft oranges from lln~1~m~geci ones is described in Bryan, Anderson, and Miller, "Mechanically Assisted Grading of Oranges for Processing," 21(6) Tr~ne~ction.e ofthe ASAE 1226-1231, (1978). Finney, "Meçh~nic~l Resonance within Red Delicious Apples and its Relatiûn to Fruit Texture," 13(2) Tr~n~çtions ofthe ASAE 177-180 (1970) describes non-destructive techniqu~e basedon resonanl frequencies to evaluate filll.lless of apples and peaches. The concept of using resonant modes in a sorting m~t~.hine is described in Peleg, U.S. Patent No.
4,884,696. (1990). In addition, blueberries and grapes have been sorted by low frequency vibration, Chen and Sun, "A review of non-destructive methods for quality evaluation and sorting of agricultural products," J. Agric. Engng. Res. 49, 85-98 (1991).
Nuclear m~gnetic leson~ e data from fruit has also been used, Stroshine, Cho, Wai, Krutz, and Baianu, "Magnetic I ~sonance sensing of fruit firmness and ripeness," ASAE
teçhnic~l paper no. 91-6565, ASAE, St. Joseph, MI (1991).
Both the non-destructive contact sensors and the sensors that rely upon secondary characteristics share the common problem that they are meçh~nically complicated and are too slow for packing house operations. A common ~iffic..lty is the 25 need for mechanical contact between the product and the sensor. Mechanical devices limit the speed of operation (except for vibration) and can limit reliability. Speed is also limited in some of the approaches by the need to completely analyze the signal generated. Secondary methods, such as measuring resonant frequencies to evaluatefirmness (which may involve striking the fruit with a hard object) often requires that the 30 impulse location be held consL~ll for repeatability. Moreover, there is a need to correlate the results obtained with force-de~ alion relationships of the fruit which are W095/07772 2 ~ 71 ~1~ PCT/US94/10349 .

S

important to end users and other buyers.
Several non-contact firmness sensors have been developed in testing human eyes - for glaucoma. For eY~mrle, the tonometers of Stauffer (U.S. Patent 3,181,351) and the app~ s of Motrh~nh~rhlor (U.S. Patent No. 3,232,099) deform the eye with puffs of 5 air, illnmin~te the point of deformation with non-coherent light, and then determine the amount of dero.ll.alion based on the intensity ofthe light reflected offofthe point of defol...alion. However, these devices are incapable of measuring the firmness of objects with rough surfaces (e.~. ~uits) because the intensity ofthe light reflected offofthe surface is a function of both the amount of dero....aLion and the rollghne.ee of the 10 refiecting surface - a highly variable pa- ~ el in fruits and many other products.
Mo.eove., tonometers deei~ned for testing human eyes are not suitable for testing objects with widely varying ranges of Llllness, e.g., tom~toe~e and apples; furthermore, they are adapted to test objects of rather uniform size, ~ll~Aily, and firmness and must be carefully aimed at a specific poin~ (the front of the eyeball) to obtain valid 15 measu.t;...e..ls.
There is thus a need for a method and apph~ s of testing entire lots of ~uit effectively, efflciently and non-destructively. There is further a need to directly measure firmness rather than secondary prope~ lies, and to do so without ...echallically cont~cting the fruit so as to avoid possible damage thereto. It would also be desirable to have a 20 method and app~ s for testing the L--~uless of objects having variable surface properties, such as rough surfaces with variable reflectance.

.

~1 \919 6 SU~IMARY OF T~E INVENTION

It is thus an object of the invention to provide a method of directly testing the L~ ness of fruit and other objects efficiently.
It is a further object of the invention to provide a non-contact method of testing v fruit and other objects for Llll~,ess.
It is a still further object of the invention to provide an efficient non-destructive method for testing the firmness of objects, inr,l~ldin~ fruit.
A still further object of the invention is to provide a non-destructive method for testing the Lllnness of objects having variable surface characteristics.
To accomplish these and other objects, the subject invention non-destructively measures the L"~lness of food products, and other items (~, tennis balls) where L~h~ess is a key indicator of quality, without meçh~nir~lly cont~r,ting the object under test by deforming the surface of the object under test and using a displ~cemPnt sensor to measure the surface d~;ro""aLion. The measured surface derc"~l.alion is then correlated to the firmness of the object under test. Several methods may be used to deform the surface. Preferably, dero~lllaLion is accomplished by impin~in~ an impulsive jet of a fluid (Ç L, air) onto the surface, although other methods could be used.
Several measurements may be useful for co"ela~ g surface dero,lllalion to the L"luless of the object. These inrl~ldP., but are not limited to, measuring the rliet~nce between a fixed point on the firmness measuring device and the object under test before the impulsive jet impinges the object and colllpal;l g that ~liet~nce to the distance when .;..""" dero""aLion ofthe object under test has occurred.
Two other measurements which can be correlated to r" ,l,ness are the rate at 25 which the surface of the object under test deforms as the impulsive jet is applied to it, and measuring the rate at which the surface of the object under test lt:cove;l~ to its nondeformed state after the impulsive jet has ceased.
The displ~r,Pm~nt sensor used operates by exposing the object under test to one form of energy (~g., ultrasound; electro-m~gnP,tic radiation, such as visible light;
30 microwave radiation; and x-ray radiation). The displ~cçmrnt sensor can be an off-the-shelf laser displ~rçmrnt sensor, a laser displ~cçmrnt sensor specifically dçeigned for use WO 95/07772 2 1 7 ~ 9 7 q PCT/US94110349 in the fi-~ ess measuling device, or any other dieplAc~ measuring device capable of measuring d~follllalions in the objects under test.
The plefellt;d embodiment uses an impulsive jet of air to deform the surface of the object and measures the amount of d~rolln~Lion with a laser displ~c~m~nt sensor - 5 C~, Keyence LB-l 1, available from Keyence Corp. of America, Fair Lawn, N.J.). The impulsive jet of air i~llpillges the surface of the object with a fixed, predetermined force.
The amount of defollnalion is determined by measuring the tli~t~nce from a laser light source to the deformed area of the object and back to a light detector near the laser light source.
The amount of defollllalion is then correlated to the firmness of the object.
Although in some in~t~nces this could be done by direct calc~ tion, detelll~inillg the firmness of a particular class of objects as a function of surface defo, malion may also be done through empirical testing. After a sample of sufflcient size has been tested, a standard table of fil Illness versus surface defc,llllaLion can be created. Once this has been accomplished, firmness can then be determined by correlating the amount of surface defolll,a~ion of the object under test to its firmness, such as by curve-fitting teçhniql1es or table-lookup, possibly with interpolation.
Displ~c.om~nt can be directly displayed by the inventive appal~ s, which would allow one either to calculate displ~ m~nt directly or to look up the L~lllness of the object under test in a table which lists firmness as a function of displ~c~mPnt Alternately, the displ~cçmPnt signal can be supplied in analog or digital form to a firmness indicating device, suitably calibrated to ll~lsrOIlll the supplied signal into a display indicating the firmness measurement. Automatic means such as a digital computer can also be used by supplying the displ~c~m~nt signal in a form suitable for input into the computer (e.g., a digital signal). The computer can then autom~tic~lly perform the c~lclll~tions necçssA~ y to compute fi~ ess and/or degree of ripeness (for fruit, r""~i~ess would co"~,lale to the measured r",llness in a known way -- perhaps determined empirically -- for each particular type of fruit) and display it in a suitable fashion or control automatic processing and/or p?~Çl~in~ equipment.
This device can be employed as a fixed unit for firmness testing in a p~çl~ing house or a factory. In a packing house it would be used to sort fruits and other food W O 95/07772 PCTrUS94/10349 ~111979 products. It would test the firmness of the fruit, correlate the Ll~llness with the .ipelless of the fruit (or some other predetermined quality of the fruit), and then control a means to put the fruit into a preselected location based on its ~.llness.
It could also be employed as a bench-top tester used in a p~cl~ing house for 5 process control. In this application it would be used for random sampling of the output of line sorters for quality control and line calibration.
It could also be employed as a portable unit for firmness testing in the field of food products (~, as a hand-held device used to determine optimal fruit harvest time) or other products where fi,ll..less is an important factor (~, tennis balls used in 10 tournament play). As an in-the-field fruit tester, it would test the firmness offruit while still on the tree to determine if it is of the proper ripeness for harvest.
This device has several advantages over the prior art. These include: the def~llll~lion force is distributed over all of the test area of the surface of the object as opposed to only the raised portions of an irregular or "bumpy" test area, as would a 15 mec.l~nic~l device, thus Ill;~-;lll;,.;ilg the damage to the tissues ofthe object by distributing the applied pressure over a greater surface area rather than concenll ~ling it at one or a few discrete points corresponding to the bumps. The fluid jet has a relatively short acceleration time colllpared to a ,--e~ ic.~l deformation device with its greater inertia and which is therefore un.~l-it~hle for pa~ing house operations requiring multiple 20 tests per second; it can be constructed from relatively inexpensive, commercially available parts; and the aiming, size and tolerance of the components is not critical:
repeatable relative measurements are sufficient to provide acceptable quality il~....aLion.

WO 95/07772 2 1 7 1 ~ 7 9 PCT/US94/10349 .

BRIEF DESCRIPTION OF TF~E ~IGURES
FIG. 1 is a drawing ofthe plere,.ed embodiment of a r""~ness sensor in acco, dal~ce with the invention.
FIG. 2 is an alternative embodiment of a fl"~ess sensor wheleill the inc~ nt S laser beam is not conc~. .l . ic with the center line of the nozzle.
FIG. 3 is a drawing of the laser displ~c~m~nt sensor used in one embodiment of the invention.

DETA~LED DESCRIPTION OF T~E ~NVENTION
The p-ere,led embodiment, as seen in FIG. 1 at 10, comprises an impulsive air-jet generating unit 20, a surface dero""alion measuring unit 60, a control unit 100 and an analyzing unit 120. Impulsive jets of air from the airjet generating unit 20 are aimed at a selected point or area 155 of the surface of the object under test 150. It is an advantage of this invention that variations in surface reflectivity and texture are 15 relatively unimportant in selecting the point or area 155 because the method used for dete"""fing deroll~ ion is not critically dependent upon the absolute reflectivity of the surface, as will be explained below. The impulsive air jets from the airjet generating unit 20 deforrn the surface lS5 of the object under test 150 to a greater or lesser extent depending on the following factors: predetermined pressure of the impulsive fluid jet, 20 time duration of the fluid jet, density of the fluid used, and di~meter of the fluid jet. The mec.h~ni~m is one of l,~1srel ofthe kinetic energy in the air stream to the mass ofthe object under test.
The airjet genel~ling unit 20 comprises an air supply 25 which provides air at apressure not less than the desired pressure of the impulsive air jet to a pressure regulator 25 30. The pressure regulator 30 disch~ es at the predetermined pressure of the impulsive air jets to the accllmlll~tor 3S. The acc.-m--l~tor 35 acts as a reservoir, holding enough air for an impulsive jet of sl-ffi~i~nt duration to deform the object under test. It discharges air through the solenoid valve 40, which, under the control of the controller 100, meters the 21 7 1 q7q impulsive air jets to the nozzle 45. The nozzle 45 directs the impulsive air jets to the selected area 15S of the object under test 150.
The acç-lm~ tor 35 must have the capacity to store enough fluid at sufficient pres~l,t; such that the impulsive jet from the nozzle 45 is of sufficient duration to 5 deform the object under test 150.
In one embodiment of the air jet generating unit 20, used in the firrnness testing of apples, the following speçific~tions were used:

supply air ples~ule 140 psia air density in air jet stream 0.0735 Ibs/cu static pressure in air jet stream I4.7 psia impact pressure to deform surface 25.0 psia mass flow rate 0.080 Ibs/sec nozzle~ metPr 3/8 in ~ccl-mlll~tor tel.lpe~ re 520 R
time duration of jet pulse 20 milliseconds max accl-mlll~tor pressure drop 5.00 psi max solenoid valve pressure drop S.00 psi min accllm~ tor volume 1.60 cu ft connectinp pipe ~i~mP,ter O.S0 in gas flow velocity 97.65 ft/sec The above specifications should not be taken as limitations but merely as an example of empirically dete~ll"ned pa~ ers that were found to be suitable for use in 5 one application.
For most applic~tion~ in which fruit is being tested, the surface impact ples~ule will typically be in the range of O.S to 60 psia and the length of time that the surface 15S
will typically remain deformed will be in the range of 3 to 20 milli~econds. The surface 155 will not be deroll,led i~ eously, but will require a jet of air sl-st~ined for a 30 sufflcient period to deform the surface (eg., in testing apples, it was found to be sufficient to sustain the impulsive jet for 3 to 20 milli.~econds) WO 95/07772 ~ 1 7 ~ q 7 9 PCT/US94/10349 In one embodiment various items were tested using both a firmer sample and a less firm sample. The following impact pl`e~ul`eS were applied to each item to achieve - the following measult;nlel,ls:
Item Impact S Tested ~les~ule (psia~Firmness (N) Deflection (mm) Kiwifiuit 30.0 1.7 0.83 30.0 2.6 0.20 Ne~ f' 19.0 1 .0 0.30 19.0 5.4 0.08 Orange 23.0 6.8 0.24 23.0 8.2 0.18 Plum 2~.0 14.2 0.70 25.0 45.5 0.13 Potato 45.0 91.0 0.14 45.0 86.0 0.19 Hot Dog 15.5 8.6 1.16 15.5 11.0 0.70 25 (Where N is relative firmness, in Newtons, as measured by the Magness-Taylor method with an 8mm (li~met~r probe.) The area deformed by the impulsive jet of fluid is typically about 0.2 inches inrii~m~.ter, ~ltho~lgh this area may be adjusted by adjusting the size of the nozzle for any particular application. The di~t~nce from the nozzle 45 to the surface of the object 30 under test 155 is not critical as long as the velocity of the impinging air is sufflcient to deform the area 155 of the object under test 150. A greater the distance from the nozzle to the surface ofthe object results in greater ~ nl.~tion ofthe velocity ofthe air jet.
The surface-derolll.alion measuring unit 60 comprises a laser 65 and pl~cçm~nt detector 70. The laser 65 generates an coherent incid~nt light beam 7535 aimed at the selected area 155 ofthe object under test 150. A coherent reflected light beam 80 is reflected from area 155 and returns to the light detector 70. A feature of the invention is that light beam 75 need not be precisely aimed at the center of the area deformed by the impulsive fiuid jet, since only relative measurements of derc.lmalion are required to evaluate product quality in most in.~t~nces It is sufficient that the light beam WO 95/07?72 ~ PCT/US94110349 ~ 7 1 979 12 7S be aimed sufficiently near the center of the deformed area to obtain repeatable relative measult;."e.lLs of dero----a~ion. In addition, although it is preferable that light beam 75 be coherent, it is not l-to.cçss~ . y that it be either coherent or monocl~ l.aLic, as long as it can be focused on a sufficiently small spot over the range of d~ro.~ Lion 5 di~t~nce to be encounlered, and that it is accurately detect~ble by the derollllalion sensor. Monochlo~la~ic coherent light is ple~lled, however, because the use of such a light source simplifies focusing and detection techniques.
Commercially available surface-d~rc llll~Lion measuring units suitable for this purpose are available from Keyence Corp. of America, Fair Lawn, NJ. As shown in 10 FIG. 3, the "LB" series displ~fçm~ont sensors (e.~., LB-l 1 and LB-12) detect targets using tri~n~ ,tion by means of a semiconductor laser 65. The laser 6S is powered by a drive circuit 68. The inci~ent beam of light 75 from the laser 65 is focused on the target by a lens 66. The target surface 155 reflects a reflected beam 80, which is then focused on a position-sensitive detector (PSD) 74 by a lens 72, forming a beam spot. In general, 15 the PSD 74 may comprise a plurality of photodetectors or photocells which are connected to one or more di~~ ial amplifiers 76.
Tri~n~ tion is then accomplished by deLelll h~ing the difference in the intensity of the part of the beam 80 striking each of the spatially separated sensors in the PSD 74.
The difference in intensity results in differing signals from the photodetectors or 20 photocells, which are related to the amount of displ~cçment and the diffil~en~ss of the reflection. These differing signals are amplified and processed by the one or more di~le..Lial amplifiers 76 which supply an analog voltage signal represe~tative of displ~ement As shown in FIG. 1, the incident beam 75 passes through a L-~ls~a-t;llL window 25 82 in the impulsive air jet gene.~Lillg unit 20 such that it is substPnti~lly concentric with the output of the nozzle 45. It is aimed near the center of the area on the surface lS5, but can aimed anywhere within one half of the radius of the nozle 45 from the center of the area 155.
The reflected beam 80 also passes through the window 82 to return to the 30 detector.

The object under test 150 may optionally be held in place by a means 152 for preventing its movement such as a clamp, a hollowed out block, or a dimple on the surface of a conveyor belt. Any other suitable holding means may also be used. This ensures that the object 150 does not move while the firmness measurement is being 5 made. With the proper selection of process parameters the air jet application and disp!acP.m~nt sensing can take place in a period short enough that the movement ofthe fruit on a conveyor line would not affect the result of the test, thus dis~e~ g with the need for a means for preventing movement. Two methods of dete~ ling if the fruitbeing tested is in the proper position to be tested can be employed: a photo sensor (not 10 shown) could detect an object (the fruit) crossing a position on the p~c1ring line near to the testing device and trigger a test, or the displ~cçn~nt sensor itself could trigger a test when it detects a ,..in;...,.... in the rii~t~nce between the sensor and any object under it.
More likely, a packing house line would use a col,lbina~ion of the two: the photosensor would detect the presence of fruit and alert the rli~pl~cçmpnt sensor to start looking for a minimllm Insofar as the operation of the invention is concerned, any fluid which is capable of measurably d~rollll,ng the surface 155 of the object under test 150 and is Llalls~alenL
to the laser beam 7~ C~, air, nitrogen, etc.) may be used in the impulsive jet. The jets used to deform the object under test can use specific gasses (e.g. nitrogen or helium for testing objects which might be damaged by being exposed to oxygen; or SF6, which is much heavier and denser than air, for testing objects requiring a more forceful jet in order to be deformed) supplied from a pressurized source, or jets of liquid supplied from a liquid reservoir to deform the object under test. Fluids, such as liquids, that would scatter light from the laser beam 75 could be used if they are aimed at the object under test 150 in such a way that they do not interfere with either the inciclçnt laser beam 75 or the rçflected laser beam 80.
The surface-d~;~olmaLion measuring unit 60 outputs an analog signal whose voltage ~eplesellls the di~t~nce between the measuring unit 60 and the object under test 150. This signal is fed into the analyzing means 120.
The analyzing means 120 is triggered by the control unit 100 to analyze the analog signal from the measuring unit 60 near the moment of maximum deformation.

Conventional peak-detecting circuitry can be used to locate and measure the peak of the analog signal after triggering. An oscilloscope (not shown) can be used to determine the amount of dero,l"a~ion based on peak voltage displayed, the rise time of the voltage signal or the fall time of the voltage signal. Analyzing means 120 may also comprise an S analog filtering circuit and meter calibrated to in-lic~te r""llless. If desired, the analog signal from measuring unit 60 can be converted to a digital signal by an analog-to-digital converter for further proceccinE The surface-d~ru,..-a~ion output may be analyzed and used to control the sorting operations of a p~c~ing house. Analysis may typically include the dt;~."..ndlion of firmness and/or ripeness.
Firmness may be de~e.. lil~ed by correlating the amount of deformation of theobject to its associated firmness. Two other methods to determine firmness are measuring the rate at which the surface of the object under test deforms as the impulsive jet is applied to it, and measuring the rate at which the surface of the object under test recovers to its nondeformed state after the impulsive jet has ceased.
An ~ltern~tive embodiment is shown in FIG. 2. This embodiment follows the same principles of the embodiment of FIG. l, except that it does not have the window 82 of FIG. 1, the.t;rore the inr;d~nt laser beam 75 and the reflected laser beam 80 are not sul; s~ lly concentric with the nozzle 45. The embodiment of FIG. 2 would belimited, in that care should be taken in this embodiment to avoid interference by the 20 nozzle 45 with the operation ofthe disp!~c~m~nt sensor 60 by blocking the in~idçnt laser beam 75. There are two problems associated with this configuration: first, if the laser beam 75 is focused on the center of area 155 of the fruit to be tested 150 prior to the impact of the impulsive jet, then once the surface is deformed, the laser beam 75 will no longer be aimed at the center; and second, if the laser beam is at an angle to the 25 impulsive jet, then, if one draws a right triangle with the axis of the laser beam 75 being the hypotenuse and the axis of the impulsive jet being the cosine side, the amount of d~.malion of the fruit 150 will be determined by the change in the position of the surface 155 along the cosine side axis. However, the tli~pl~em~nt sensor 60 willmeasure the change in position along the hypotenuse side, giving an incorrect 30 measurement that will have to be subsequently corrected.

WO 95/07772 2 ~ 1 1 9 79 PCT/US94/10349 It is possible to direct the light from the laser to the object under test via a fiber optic line passing through the nozzle. This would have the advantage of il~lpl oving fluid flow, as the laser source could be concel.ll;c with the nozzle without having elbows in the fluidl line.
The actual amount of defo- .l.aLion of the surface 155 caused by the impulsive air jet is not critical, although it must be within a range that can be sensed and measured by the surface-deroll..alion measuring unit 60 and should be insufflcient to damage the object under test. The amount of dero.lnalion caused by a jet of any particular duration and force may readily be determined by direct measurement by the surface-derol malion 10 measuring unit 60. The force and duration of the jet may be adjusted, if necessa~y, so that the range of derc" ",aLions likely to be encountered for the class of objects under test is accommodated within the range that can be ll,ea~ul ed accurately by the surface-derolmalion mP~ellring unit 60. There is no neces~;ly that the surface 155 of the object under test 150 be fl~ttened or to reach any particular degree of convexity or concavity.
1~ It is only necess~y that the range of fi.m..ess sought to be measured can be h~..ed from the measured relative dero.lllalion ~i~t~n~es and that the object under test not be destroyed by pelrolll.ing the test.
Because it is the relative d~rull..aliûn ofthe object under test 150 that is measured, it is not "ecçs~.y to carefully select the portion ofthe surface 155 under test.
20 Concave, convex, and flat surfaces can all be tested for firmness.