CA1253232A - Active tactile sensor apparatus and method - Google Patents
Active tactile sensor apparatus and methodInfo
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Abstract
ABSTRACT OF THE INVENTION
A tactile sensing apparatus having a piezoelectric energizing layer with a plurality of conductors disposed on one surface of a piezoelectric material and a plurality of conductors disposed on the opposite surface of the piezoelectric material, the plurality of conductors having electrical connections connected to electrical energizing means. An electrical insulating layer is disposed adjacent the piezoelectric energizing layer. A second piezoelectric sensing layer is disposed adjacent the insulating layer, and has conducting surfaces disposed on opposite surfaces thereof. The conductors in the piezoelectric energizing layer provide N x M energizing areas with N + M electrical connections to the energizing layer. Further apparatus may include an oscillator, an optional amplifier and a switching means or multiplexer for the input signal.
The apparatus may optionally have more than one piezoelectric energizing layer as well as more than one piezoelectric sensing layer. PVF2 is the preferred piezoelectric material. An optional base material and protective layer may be used.
A method of operating the tactile sensor includes providing a variable frequency electrical signal at a frequency and amplitude adapted to energize the energizing areas. The signal is switched to the conduc-tors to energize selected energizing areas of the energizing layer in a predetermined sequence. The signal generated in the sensing layer that varies in frequency and amplitude in response to an object in contact with the tactile sensor is processed for frequency and amplitude information to determine the characteristics of the object such as shape, force or weight.
A tactile sensing apparatus having a piezoelectric energizing layer with a plurality of conductors disposed on one surface of a piezoelectric material and a plurality of conductors disposed on the opposite surface of the piezoelectric material, the plurality of conductors having electrical connections connected to electrical energizing means. An electrical insulating layer is disposed adjacent the piezoelectric energizing layer. A second piezoelectric sensing layer is disposed adjacent the insulating layer, and has conducting surfaces disposed on opposite surfaces thereof. The conductors in the piezoelectric energizing layer provide N x M energizing areas with N + M electrical connections to the energizing layer. Further apparatus may include an oscillator, an optional amplifier and a switching means or multiplexer for the input signal.
The apparatus may optionally have more than one piezoelectric energizing layer as well as more than one piezoelectric sensing layer. PVF2 is the preferred piezoelectric material. An optional base material and protective layer may be used.
A method of operating the tactile sensor includes providing a variable frequency electrical signal at a frequency and amplitude adapted to energize the energizing areas. The signal is switched to the conduc-tors to energize selected energizing areas of the energizing layer in a predetermined sequence. The signal generated in the sensing layer that varies in frequency and amplitude in response to an object in contact with the tactile sensor is processed for frequency and amplitude information to determine the characteristics of the object such as shape, force or weight.
Description
~253~32 ACTIVE TACTILE SENSOR APPARATUS AND METHOD
FIELD OF T~IE INVENTION
This invention relates to a tactile sensor and a sensing method that can be used to detect contact 5 between the sensor and another object. Some of the properties that can be sensed are shape, texture, pressure, position and orientation. The sensor and sensing method have utility in industrial machinery, robots, medical devices and prosthetic devices.
BACRGROUND OF THE INVENTION
Robotic devices and systems are finding increased usage in a variety of applications. They extend into the realms of medicine (e.g. prosthetic devices), 15 military applications, industrial robots (for assembly), hazardous industrial environments and so on.
For a robotic device to operate intelligently within a given but flexible and changing environment, it must be able to accurately determine, or sense, 20 what its surroundings are. Advanced sensory capabilities will characterize the next generation of robots, and among these sensory functions is tactile sensing, the ability to determine physical features through touch mechanisms. Although the goal can be stated 25 quite simply, the technological implementation presents quite another challenge. Furthermore, the tactile sensing capability is a broad spectrum: at one end of the spectrum is the ability to merely detect the presence of an object, and at the other end is the 30 ability to determine the surface texture of an object.
Rounding out the spectrum is the ability to determine an object's size and shape and whether or not it has moved on the sensor's surface.
An example of a piezoelectric device is U.S. Patent 35 4,328,441 (Kroeger, et al) and its international counter-part WO 81/02223. These reveal a layered structure ~53232 having piezoelectric polymer films on opposite sides of an insulating layer for the purpose of providing a keyboard. This does not avoid the phantom point problem.
IBM Technical Bulletin, Vol. ~0, No. 1, J.P.
Dahl, June 1977, reveals a scanned piezoelectric keyboard switch where each key is chosen to have a uni~ue inherent resonant frequency while the switches are wired in parallel. Contact dampens the f lequency and the imped-10 ance of the undampened crystal changes greatly.
I~M Technical Bulletin, Vol. 20, No. 7, J. Fajans, December 1~77, discloses an acoustical touch panel in which acoustic plane wave impulses are generated at fixed times in orthogonal directions by two long 15 piezoelectric crystals mounted on adjacent sides of a lower plate. ~ocal acoustical coupling is said to result in a spherical wave originating from the point of contact in an upper plate when an impulse is present in the lower plate.
P. Dario et al, "Touch Sensitive Polymer Skin Uses Piezoelectric Prop~rties to Recognize Orientation of Objects", an article in Sensor Review p. 194-198, October 1982, use a single layer polyvinylidene fluoride PVF2 sensor with 256 sensing areas (16 x 16 array) 25 to recognize object orientation. One lead pin is required for each sensing area.
A bilaminate PVF2 sensor is proposed in "Piezo-Pyroelectric Polymers SXin-~ike Tactile Sensors for Robots and Prostheses", 13th Symposium 7 Conference 30 and Ex~osition on Industrial Robots and Robots , Chicago, R. Bardelli et al, April 1983, where the outer layer senses temperature and the inner senses mechanical forces. The article teaches against row by column reading involving multiplexing. A lead for each sensing 35 area is advocated.
In "Piezoelectric Polymers: New Sensor Materials for Robotic Applications", 13th Symposium on Industrial ~;~53~:32 Robots and ~obots 7 Conference and Exposition Chica~, P. Dario et al April 1983, various PVF2 contact sensors and touch sensors are described. The touch sensor using 256 sensor regions has at least 256 leads.
5 A tactile sensor using a PVF2 emitter and receiver uses the time of flight of ultrasonic waves through a compliant material to measure pressure on the sensor.
In the prior art there are several major disadvan-tages that are overcome by the present invention.
10 First the location, shape, and pressure of an object can be actively sensed. Secondly, switching noise problems are overcome by multiplexing the energizing signal rather than the sensing signal. Third, the invention avoids the "phantom point" problem of a 15 crossed array. Fourth, great sensitivity and high resolution are possible. Finally, the complexity of the lead array can be greatly reduced by allowing the use of N + M leads to address N x M active areas.
In accordance with the invention there is provided an apparatus for tactile sensing. One embodiment of the apparatus is basically a sandwich structure of several layers. A first layer of piezoelectric 25 energizing material is used to interrogate the sensing layers. The first layer ma~ have parallel conductors or electrodes on two sides thereof with rows of conductors on one side and columns of conductors on the other.
Other patterns can be used but this pattern was found 30 useful for multiplexing techniques.
An insulating layer separates the piezoelectric energizing layer from a piezoelectric sensing layer that is used as a signal source to detect pressure on the apparatus. The sensing layer may contain two 35 conducting layers on opposing sides of a piezoelectric material. PVF2 is the material of choice for the piezoelectric material for both the energizing and ~2S3~
sensing layerO A base material and outer protective layer, may optionally be a part of the design as well as a multiplexer that is integral with the sensor.
Unlike conventional tactile sensors, this tactile 5 sensor has both a static and dynamic response. When an object contacts the transducer, the sensing layer is flexed, generating a small cutput transient voltage.
However, by continuously AC stimulating areas on the energizing layer (defined by the intersection of one 10 row conductor and one column conductor), an acoustic wave is transmitted through the insulating layer, which in turn stimulates the sensing layer. The output is then a continuous AC signal with a frequency equal to the stimulating frequency and an amplitude correspond-15 ing to the efficiency of acoustic coupling betweenthe layers. When an object comes in contact with the sensor, the acoustic coupling is changed, and the output signal amplitude is consequently changed.
Depending on the frequency of stimulation and the 20 amount of contact force, the acoustic coupling may be dampened or enhanced, and the output signal amplitude is reduced or increased, respectively. By multiplexing the stimulated points on the driving layer--not the signal from the sensing layer--absolute knowledge 25 of when the signal is produced is preserved, without the inherent "dead time" associated with output signal multiplexing. By noting the amplitude of the output signal, the amount of applied force can be determined, and by correlating the multiplexing address to the 30 output signal, the shape of the contacting object can be determined. Even though time multiplexing with row and column addressing was used in the present design, frequency multiplexing can be applied, as well, to obtain the tactile information.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates, in semischematic form, one embodiment of the tactile sensor of the invention.
Figure 2 i]lustrates an embodiment of electrodes ~53~32 used in the energizing layer.
Figure 3 illustrates a top view of one embodiment of the arrangement of conductors of the energizing layer.
Figure 4 illustrates a top view of one embodiment of the superposition of the two layers of electrodes used in the energizing layer.
Figure 5 illustrates one embodiment in semischematic form of the arrangement of various electronic devices 10 to the apparatus of Figure 1.
Figure 6 illustrates in semischematic form another embodiment of the invention wherein two energizing layers are used.
Figure 7 illustrates the typical output characteris-15 tics of the tactile sensor.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENT
_ Figure 1 illustrates one embodiment of the tactile sensor 100. This embodiment comprises a base material 20 101 that is preferably nonresilient. This base surface may be flat or of arbitrary curvature. If desired a resilient material 102 may be placed adjacent to the base material 101; however, this is optional.
An energizing layer 103 is disposed adjacent to the 25 base 101 or optional resilient material 102. Layer 103 is composed of electrodes 105 and 106 on two opposing surfaces of piezoelectric material 104. Electrodes 105,106 may be parallel arrays of electrode bars or conductors as in Figures 1 and 2 or as interconnected 30 discrete pads as shown in Figures 3 and 4. The electrode bars 105,106 are arranged so that they run at right angles and produce an array of surfaces where the surface of one bar is opposite that of another. These surfaces 210,211 stimulate the active site 220. This 35 surface 220 is the active site as explained below and as shown in Figure 2. Adjacent to the electrodes 106 is an insulator 107. Insulator 107 may be composed of an insulatincJ sheet or may be of an insulating adhesive. Preferred embodiment is less than 1/32 ~0 inch latex rubber coated with resilient adhesive on ~:5~3~32 both sides. A second piezoelectric sensing layer 10~ is positioned adjacent to the insulating layer 107. This sensing layer 108 is composed of a piezoelec-tric material 109 with a conductor 110,111 on opposing 5 surfaces. This piezoelectric sensing layer 10~ is preferably resilient. Finally, an optional resilient protective layer 112 may be used to protect the sensor 100 from the environment.
Figure 2 illustrates in an exploded view the 10 arrangement of the energizing layer 103 in greater detail. This layer 103 is composed of a plurality of conductors 105 disposed on one surface of layer 103 and a plurality of conductors 106 on the opposite surface. If conductors 201 and 202 are energized 15 then an energizing area 220 is defined. The energizing area is produced whenever portions of conductors 105,106 are formed at opposing surfaces. Applying an energizing signal to the appropriate conductors through a multiplexer 505 energizes the device.
Figure 3 illustrates a preferred embodiment of one set of electrodes 105,106 of the apparatus. A
typical electrode 300 is constructed of connecting pad 301 and individual electrode pads 302 that define energizing areas 220. E~ternal electrical connection 25 is made to the connection pads 301 and electrode pads 302 by lead connections 303.
Figure 4 illustrates a top view shows a preferred embodiment of one embodiment of electrodes 105,106 as they would be arranged when superimposed on opposite 30 surfaces of piezoelectric energizing layer 104. Thus electrodes 300 are placed at right angles to electrodes 400. The overlaps of two electrode pads 402 defines an energizing area 220.
One of the great advantages of the invention 35 is that the number of electrical connections required is greatly reduced, for a given number of energizing areas. Conversely, for a given number of electrical ~2532:32 connections the number of energi~ing areas is greatly increased. For example, in a rectangular array as iilustrated in Figure 4 where N is the number of connec-tions along the horizontal axis and M is the number 5 of connections along the vertical axis, N ~ M connections allow N x M energizing areas. Thus the particular embodiment shown in Figure 4 where N - 16 and M = 16, 32 connections allow 256 energizing areas.
These energizing areas correspond to sensing 10 areas in the sensing layer. These sensing areas are spatially located on the sensing layer in the same manner as the energizing areas on the energizing layer.
Only pressures located at a point: corresponding to the sensing energizing area will be measured as further 15 discussed below.
The pattern or layout of the conductors and pads may be rectilinear as shown in Figure 1-6 or be in a circular or in any arbitrary shape providing sensing information specific to the desired application.
Figure 5 illustrates one embodiment of the electron-ics associated with the tactile sensor 100. Signal generator 501 is connected to amplifier 503 by leads 502. The amplifier 503 is in turn connected to switching means or multiplexer 505 by leads 504.
Signal input to the tactile sensor apparatus 100 is through electrical connecting leads 506. Leads 506 may be N + M in number where the conductors in the energizing layer are adapted to provide N x M
array of energizing areas 220 in the embodiment of 30 Figure 1. Leads 506 may number an additional P + Q
for an P x Q array in the embodiment of Figure 6 discussed below. The output signal from the sensing layer 108 is directed to amplifier 509 by leads 508. The output of amplifier 509 is sent. to a signal processing means 35 511 by leads 510. Signal processing means 511 converts the information contained in the signal of amplitude and frequency to display and/or control apparatus 513 by leads 51~. Leads 514 and 516 from the signal ~:~53~
processor 511 are optional being required only if the switching means or multiplexer 505 and oscillator 501 are to be controlled by information from the signal processing means 511.
Optionally electrical switching means or multiplexer 505 and leads 506 may be built with the tactile sensor 100 as one unit. This would provide lower wiring complexity and reduce signal interference from other devices. The switching means 505 may be optionally 10 mounted on the base 101 of the apparatus or other suitable place. The oscillator 501 may be fixed or variable in frequency.
In general the apparatus of the invention may be described as comprising a piezoelectric energizing 15 layer 103 having a plurality of conductors 105 disposed on one surface of a piezoelectric material 104 and a plurality of conductors 106 disposed on the opposite surface of the piezoelectric material 104, the plurality of conductors 10~,105 having electrical connections 20 301,401 adapted to be connected to electrical energizing means (not shown); an electrical insulating layer 107 disposed adjacent the piezoelectric energizing layer 103; and a piezoelectric sensing layer 108, having conducting surfaces 110,111 disposed on opposite 25 surfaces thereof, and disposed adjacent the insulating layer 107. Details of the above device include:
conductors in the piezoelectric energizing layer 103 that are to provide N x M energizing areas with N + M
electrical connections to the energizing layer 103, 30 wherein N x M > l; electrical energizing means for driving said energizing layer and electrical processing means for processing signals from the piezoelectric sensing layer 108 and a switching means or multiplexer adapted to be connected to the N + M electrical connec-35 tions and adapted to energize the N x M energizingareas.
~L~53~3~
A further detailed description of the sensor 100 would include: a first electrode layer 105 having N electrodes 201, where N > l; a first piezoelectric polymer layer 104 disposed adjacent to the first electrode 5 layer 105; a second electrode layer 106 having M elec-trodes 202, where M > l; and disposed adjacent to the first piezoelectric polymer layer 104 wherein N x M > l; an insulating layer 107 disposed adjacent to the second electrode layer 106; a first conductive 10 layer 110 disposed adjacent to the insulating layer 107 and adapted to be connected to output processing means; a second piezoelectric polymer layer 109 disposed adjacent to the first conductive layer 110; and a second conductive layer 111 disposed adjacent to the 15 second piezoelectric polymer layer 109 and adapted to be connected to output processing means.
As mentioned previously the apparatus may optionally have a base material 101 which is typically rigid but may have another resilient layer 102 thereon. Like-20 wise a protective layer 112 is disposed adjacent tothe piezoelectric sensing layer. This protective layer 112 must be resilient to transmit forces to the sensing layer 10~.
Figure 6 illustrates another embodiment of the 25 invention wherein an additional piezoelectric energizing layer 603 is added. This embodiment 600 comprises a first electrode layer 605 having N electrodes 201, wherein N > l; a first piezoelectric polymer layer 604 disposed adjacent to the first electrode layer 30 605; a second electrode layer 606 having M electrodes 202, wherein M > 1, and disposed adjacent to the first piezoelectric polymer layer 604; a first insulating layer 607 disposed adjacent to the second electrode layer 606; a third electrode layer 105 having P electrodes 35 201, wherein P > 1, and disposed adjacent to the insulat-ing layer 607; a second piezoelectric polymer layer ~5323~
104 disposed adjacent to the third electrode layer 105; a fourth electrode layer having Q electrodes 202, wherein Q > 1, and disposed adjacent to the second piezoelectric polymer layer 104, wherein P x Q > l;
5 a second insulating layer 107 disposed adjacent to the fourth electrode layer 106; a first conducting layer 110 disposed adjacent to the second insulating layer 107 and adapted to be connected to output signal processing means; a third piezoelectric polymer layer 10 109 disposed adjacent to the first conducting layer 110; and a second conductive layer 111 disposed adjacent to the third piezoelectric polymer 109 and adapted to be connected to output processing means. Optionally, a protective layer 112 may be used as well as a base 15 101 and resilient layer. As can be seen,an additional piezoelectric energizing layer 603 and insulating layer 607 have been added to the basic design of Figure 1 and second electrode layers 605,606 are adapted to provide N x M energizing areas 220 in the first 20 piezoelectric polymer layer 603 with N ~ M electrode connections; and the third and fourth electrode layers 105,106 are adapted to provide P x Q energizing areas 220 in the second piezoelectric layer 103 with P + Q
electrode connections. Switching means or multiplexer 25 505 are connected to the N ~ M and P + Q electrode connections in a manner adapted to energize the appropri-ate N x M and P x Q energizing areas.
Figure 6 may also be described as: a first piezo-electric energizing layer 603 having a plurality of 30 conductors 201 disposed on one surface of a piezoelectric material 604 and a plurality of conductors 202 disposed on the opposite surface of the piezoelectric material 604, the plurality of conductors 201,202 having electrical connections 301,401 adapted to be connected to electrical 35 energizing means; a first electrical insulating layer 607 disposed adjacent the first piezoelectric energizing layer 603; a second piezoelectric energizing layer , ~Z~;~^3Z3~:
103 having a plurality of conductors 201 disposed on one surface of a piezoelectric material 104 and a plurality of conductors 202 disposed on the opposite surface of the piezoelectric material, the plurality 5 of conductors 201,202 having electrical connections 301,402 adapted to be connected to electxical energizing means; second electrical insulating layer 107 disposed adjacent the second piezoelectric energizing layer 103; a piezoelectric sensing layer 108 having conducting 10 surfaces 110;111 disposed on opposite surfaces thereof that is disposed adjacent the second insulating layer 107.
Another embodiment of the invention involves the use of two sensing layers rather than the single 15 sensing layer 108 illustrated in Figures 1 and 6. This additional sensing layer 108' (not illustrated) would be disposed adjacent to the existing piezoelectric sensing layer 108 with an additional insulating layer 107' between them. This additional sensing layer 20 can be used in the embodiments illustrated in Figures 1 and 6. The additional layer would allow a gradation in sensing capability with one layer sensing smaller forces than the other.
This second piezoelectric sensing layer having 25 conducting surfaces on opposite surfaces thereof, and disposed adjacent a second insulating layer may be adapted to have electrical and mechanical character-istics different from the other piezoelectric sensing layer. The layer sensing the lower forces would be 30 preferably placed uppermost in the sensor.
The device is contemplated to operate with variable frequency inputs as further discussed below. D.C.
operation of the energizing layer of the apparatus does not appear practical since the piezoelectric 35 layers have insufficient response to D.C. voltages.
For example, refering to Figure 1, for both D.C. and .
~:~513~:32 A.C. operation the passive and primary sensing ele~ent is the outer most layer of PV~2, layer 108. When an object exerts pressure on the sensor's surface, an output signal is generated. To determine the objects 5 characteristics as for example the shape of the object, single perpendicular pairs of conductors on the first PVF2 layer are energized with a voltage. If the object is not present over the junction of the perpendicular conductors, the second piezoelectric film will simply 10 expand slightly with no consequent output signal.
However, if the object is present, the sensing layer will be compressed and an output signal ~ill be registered.
Thus, by actively interrogating the N x M perpendicular pairs the shape of the object could be determined.
Another limitation of D.C. excitation of the energizing layer is the mechanical coupling between the two PVF2 layers through the insulating film.
If a 30 volt source (+15VDC, standard for many integrated analog circuits) is applied to the perpendicular conductors, 20 this energizing voltage will generate an electric field within the PVF2 film that causes a thickness expansion of approximately ten angstroms (lOA).
In order to accurately transmit this strain to the sensing film, the insulating layer 107 must be either 25 infinitely rigid or be moderately rigid and have thick-nesses on the order of this minute displacement.
Even if the D.C. energizing voltage is increased to, say, 200 V and the displacement increased to 66A, the thickness of the in~ulating material is not practical.
As a result acoustic coupling and an A.C. mode-of energizing operation is preferred.
The device is operated by providing a tactile sensor 100 having a piezoelectric energizing layer 103 with N x M energizing areas 220 and N + M connectors 35 301,401 for the energizing areas 201 and having a piezoelectric sensing layer 108 adjacent to the energizing layer 103 and electrically insulated therefrom; providing a variable frequency electrical signal at a frequency ~L253232 and amplitude adapted to energize the energizing areas 220; switching the signal to the N + M connectors in a manner adapted to energize selected energizing areas 220 of the energizing layer 103 in a predetermined 5 sequence; and processing a signal generated by the sensing layer 108 to determine the characteristics of an object that is touching the sensing layer 111 or protective layer 112. The energizing of selected energizing areas 220 may be in a predetermined sequence 10 in an algorithm driven sequence; in a random se~uence.
An algorithm may be used that provides low spatial resolution and reverts to high resolution when an object is sensed. The method can be adapted to processing a signal from the sensing layer that determines charac-15 teristics of an object touching the device or sensinglayer such as force, shape of the object or ~eight.
The method would be similar for the alternate embodiment of the tactile sensor 601; again one is switching the signal to the connectors 301,401 in 20 a manner adapted to energize selected energizing areas 220 of the energizing layers 103,603 in a predetermined sequence and processing the signal generated by the sensing layer to determine the characteristics of an object touching the sensing layer.
The signal generated in the sensing layer of the tactile sensor apparatus will vary in frequency and amplitude; by processing the frequency and amplitude information in the signal from the sensing layer charac-teristics of an object in contact with the sensor 30 can be determined.
Another method of operation is that of monitoring.
~hile in the monitor mode the energizing layer is inactive. The output of the sensing layer 111 is monitored for a given change in signal. When a signal 35 is detected the energizing system is activated and normal operation resumes. This method may be described in more detail as providing a tactile sensor having ~:53~Z:3;~
a piezoelectric energizing layer with N x M energizing areas and N + M connectors for the energizing areas and having a piezoelectric sensing layer adjacent to the energizing layer and electrically insulated 5 therefrom; providing electrical signal energizing and output processing means; monitoring the electrical output of the sensing layer to determine if an object is in contact with the tactile sensor while keeping the energizing layer and electrical signal energizing 10 means inactive; switching the tactile sensor system to active status when an output s;ignal is sensed from the sensing layer; providing an alternating frequency electrical signal at a frequency and amplitude adapted to energize the energizing areas; switching the signal 15 to the N + M connectors in a manner adapted to energize selected energizing areas of the energizing layer in a predetermined sequence; and processing a signal generated by the sensing layer to determine the charac-teristics of an object that is touching the tactile 20 sensor.
EXAMPLES 1-~
For these examples tests were done at the following forces 0,5,10, and 50g on the sensor.
The sensor was constructed in a ~ inch x ~ inch configuration. A 3/8 inch thick rigid plastic to which was bonded a 1/16 inch thick rigid platform was used for the base material. A 1/32 inch thick latex rubber material was placed over the base. The 30 piezoelectric energizing layer and piezoelectric sènsing layer (~ inch by 1~ inches) were both cut from the same PVF2 stock sheet material. Because of previous problems with separation of metallization on the layers both ~ inch wide strips (approximately 1~ inches long) 35 of metallization PVF2 were cut from a stock sheet so that the grain of metallizatlon/polymer ran parallel to the length of the strips. A 20:1 mixture of polyure-thane adhesive was prepared by adding one small drop ~2~3232 of Tycel*7200 (Lord Corporation) curing agent to .5 ml of T~cel*7000 adhesive. The mixture ~as stirred for about 1 minute and applied to the end of each strip on one side with a brush to lay down a good insulating layer. The adhesive was allowed to dry overnight. A second batch of adhesive was made and applied to one of the previously coated surfaces.
The second strip was laid on top of the first so that the two coated surfaces bonded to each other 10 with an overlap of ~ inch. The :Layers were pressed together and allowed to dry.
Because of heating problems while curing the wire bonding adhesive, the wire leads were first attached to the PVF2 strips before constructing the sensor.
15 Wire-wrap wire was bared approximately 3 mm and laid against the metallized surface near one end of the PVF~ strip. A drop of silver epoxy paste, mixed in a 1:1 ratio was dabbed on this junction and heat cured under a heat lamp for 1~ hours at 80DC. This makes 20 a solid bond with excellent electrical conductivity.
A second wire was attached to each strip on the opposite side near the same end using the same technique.
The finished sensor was then clamped using two insulated paper clips with magnetic bases and stretched 25 across the latex and base above. 0.3 inch x 0.3 inch contact areas were used ~or the weights. Detailed output signal measurements were made for a wide range of stimulation frequencies for the structure unloaded and loaded with 5g, lOg, or 50 grams. The data is 30 plotted in a single graph in Figure 7 so that comparisons can easily be made.
Test Conditions: Input voltage - lOVAC; output voltage bandwidth limited to 20 MHz to reduce the amount of noise content in the signal; load = 0,5,10,50 gm;
35 frequency range: 100 Hz to lOMHz; output voltage measured in mV peak-to-peak (mvpp).
*Trade mark.
~25~23~, This series of tests and the resulting graph of data (Figure 7) reveal considerable information on the tactile models of the device. Clearly, seYeral different trends are seen in terms of response to 5 loading. These are examined below.
First of all, both increased coupling and dampening modes are observed. At 105-110 KHz, a strong resonance is observed with increased monotonic dampening of the output response seen as the loading is increased.
In the frequencies between 2 KHz and 10 KHz, the increased coupling mode is observed for forces above and including 5 gram, while the dampening mode dominates in the 0-5 gram range; hence, the tactile mode is dependent on both frequency and loading.) 15 Two frequency crossover points between coupling and dampening modes are clearly visible. A very sharp crossover occurs at 1.2 KHz where all three loaded data curves intersect at a single point. The second frequency crossover is considerably broader and occurs 20 in the 22KHz-34KHz range.
The second main observation is that frequency shifts in resonance as a function of loading. In the 126-135 Hz range, the first resonance observed, a slight upward shift in resonance correlated with 25 increased force is observed. The same is true for the 105 KHz-llO KHz resonance discussed previously.
However, the most drastic and noteworthy is a shift that begins at 610 Hz under no load and ends up at 370 Hz for a 50 gram load. Not only does the resonant 30 frequency shift, but the amplitude increases dramatlcally.
The table below shows the summary data points of these phenomena:
~;~53~32 l?
Output Amplitude Loadinq (mv pp) Resonant Fre~uency From this response, it is apparent that the loading mass plays an important role in the resonant response of the device ~y moving in harmony with the piezoelectric ~PVF2) structure. Like a vibrating string, the PVF2 10 structure resonates at a frequency that is a function of mass. As the mass increases, the resonant frequency decreases. The increase in amplitude is probably due to increased coupling between the energizing and sensing layers of PVF2.
15 To reiterate, the phenomenon seen here is that the data points for the loaded device show a monotonic relationship at a given frequency. But, the data points for the unloaded device do not necessarily follow the same trend. This is because the response 20 is a function of loading, and the data in Figure 7 includes only loads in 5-50 gram range. In any case, the data presented here indicate strong amplitude and frequency correlations of output signal to loading.
Obviously, by performing a spectral analysis 25 of a wide band of stimulation frequencies, the precise loading could be determined and the range of possible loads may even be broadened. However, to perform such an analysis is expensive and time consuming.
To develop a sensor that responds relatively quickly, 30 say 1-10 msec for the en~ire array, and is not hardware intensive, it is better to examine a single or a few key frequencies rather than the entire spectrum.
The last point to be made concerns capacitive coupling betwee~ the PVF2 layers. This coupling is 35 always present to some extent, however, as the stimulation frequency increases, the coupling increases and eventually 3~5~3~
dominates the system so that no tactile response is observed.
In our test conditions, the coupling effect was noticeable around 300 KHz, was definitely dominating 5 the data at 700 KHz, and was the only signal observed at 900 KHz. In fact, for stimulation frequencies of 900 KHz and above, there were no observable diferences in the output signal level for various loadings. And as expected, as capacitive coupling increased, so 10 did the output signal level.
Thus, in general, the PVF2 structure must be stimulated with a signal whose frequency is well below the point where capacitive coupling interferes with the tactile response signal.
To further document the invention the oscilloscope signals for the sensor configuration used in Examples 1-4 were monitored.
The dampening mode tactile response was distinctly evident and apparent for the range of loads from 0 to 50 grams. The change in output voltage is a non-linear function of loading, but nonetheless, it is strongly correlated to the loading.
~5 A phase shift phenomenon was also observed.
This characteristic has been observed by other researchers investigating the tactile response of PVF2. The amount of phase shift may be correlated to the time of travel for an acoustic signal to propagate across the flexible 30 adhesive layer. As loading is applied to the structur~, the device becomes more tightly pressed, and the distance bet~een the PVF2 layers ~ecomes less. Thus, the time to travel and the phase shift becomes less.
The response to a sinusoidal input at resonance 35 (105 KHz) shows the dampening mode response and a sensitivity to :loads as small as one gram. Although ~;~5;~232 the change in output amplitude as a function of loading is not linear, the two parameters are correlated.
The response of the sensor to a 10 K~z square wave input was tested. This frequency was chosen because this frequency lies in the region where previously the unloaded response did not appear to correlate to the ~rend established by the loaded (5, 10, and 10 50 g) response data.
The most obvious response to the square wave input is the characteristic piezoelectric response of a decaying sinusoid, which begins with a sharp spike in response to the step stimulation and exponen-15 tially decays. Superimposed on the exponential decayis resonant ringing. As expected, the resonance was observed to ring at approximately 100 KHz.
As the device was loaded under this stimulation condition, two important changes were observed in 20 the output. First, the resonant spike and ringing continuously decreased as the loading increased.
This was expected from the data in Figure 7. More importantly, the low frequency (10 KHz) response, was also affected.
~or small loading (up to 5 grams), the load dampened the output response. The output resembled a square wave, with the amplitude decreased with increasing loading until at approximately 5 grams only the resonant response could be seen. The amplitude of the low frequency 30 stimulation and response had practically vanished.
As the loading continued to increase, an interesting reversal took place, and the output began to resemble a square wave in phase with the input. Thus, the increased coupling mode began to dominate the system, and the 35 output signal increased with loading. For 30 g loading, the resonant ringing had almost disappeared, and the low frequency response was similar to the input.
~L~25~;232 The total response to loading shows a smooth drop from 12 mvpp to zero in square wave output for the load range 0-5 grams followed by an increase in output signal to an asymptote at approximately 5 ~Ivpp. We 5 have chosen to call the force applied when minimum signal output is observed the loacl crossover point.
The load crossover point bet~een the increased coupling mode and the dampening mode is approximately 4~ grams of loading for the 10 KMz square wave. This 10 crossover point shifts up or down depending on the stimulation frequency. For example, at 100 XHz -105 KHz the crossover point has shifted upward to an undetermined point so that only the dampening mode is seen for loads in the 0 - 50 gram range.
One useful application of this frequency-dependent response is the incorporation of multiple sampling frequencies to dynamically change sensitivity without changing geometry or to verify a response at one frequency by correlation of the response at another frequency, 20 hence increasing the sensor's accuracy.
A preferred bonding or adhesive materia for the tactile sensor is Tycel ~ 7300 urethane laminating adhesive combined with 7200 Series curing agent in a ratio of 20:1 adhesive to curing agent (Hughson 25 Chemicals, Lord Corporation, 2000 West Grandview Blvd., Erie, Pennsylvania 16512~. Of course any material of similar characteristics can also be used. This nonconducting material is resilient and is used for bonding the various layers of the sensor together.
30 The above adhesive had the appropriate bonding qualities necessary to bond the various layers of the sensor to each other while simultaneously providing good acoustic coupling between the layers. It is essential that each of the layers of the tactile sensor be properly 35 bonded to the adjacent layers to provide good acoustic coupling between layers.
~;253232 A preferred embodiment for the insulators (e.g.
107) is a very thin layer of less than 1/32 inch thickness latex rubber coated with a resilient adhesive.
As mentioned earlier the piezoelectric layers 5 are preferably a piezoelectric polymer such as PVF2 and are in the form of a thin film the electrodes being formed or etched thereon on in ways generally known in the art. Preferably the electrodes are v~por deposited.
Electrical contact to the electrodes or conductors of the piezoelectric sensing and energizing layers is preferably with a silver epoxy although other materials known in the art may be used. An example of preferred electrical conducting epoxy is EPO-TEK~ H20E (Epoxy 15 Technology Inc., 14 Fortune Drive, Billerica, Massachusetts 01821~ although any similar silver filled epoxy such as those designed for chip bonding in microelectronic and optoelectronic applications may be used. The H20E epoxy used requires heat treatment; thus, temperature 20 should be kept below the temperature where the piezoelec-tric material would lose its electrical polarization.
For PVF2 this temperature should be below 120C.
A temperature of 80C was found to be suitable.
The leads are preferably attached to the piezoelec-25 tric layers of the sensor prior to assembly with the nonconducting adhesive used to hold the various layers together. This allows subsequent assembly steps at room temperature and avoids elevated temperatures that would affect the nonconducting adhesive.
As mentioned previously polyvinylidene fluoride (PVF2) is the prererred piezoelectric material. It should have its electrical polarization oriented in the thickness direction. Preferred thickness of the piezoelectric material using PVF2 is approximately 35 28~m. This is a medium size thickness that optimizes the motor and generator responses (mechanical reaction to electrical stimulus and electrical reaction to mechanical stim~lus) of PVF2. Other usable thicknesses ~ZS323:2 range from a few micrometers to as large as several millimeters.
Input voltages to the energi2ing electrical energiz-ing layer 103 of the tactile sensor lOO by an oscillator 5 501 may be fixed, variable, sinusoidal square or a suitable arbitrary wave form of single or multiple frequencies. A square wave of lK~Iz-lOKHz was ~ound to provide adequate information about the sensor response at the ~undamental frequency and higher harmonics lO and to provide adequate information for ambiguously identifying the force applied to the tactile sensor from an unknown load.
The invention solves another problem common to cross point arrays--the phantom point. For example 15 in an N = 2 by M = 2 array of conductors there are N x M = 4 points. If however three of these points are energized simultaneously the fourth point cannot be determined to be on or off. Output signals would be the same in either case. The invention avoids 20 this problem by addressing each point independently in time by the switching means or multiplexer 505.
While the forms of the invention herein disclosed constitute presently preferred embodiments, many others are possible. It is not intended herein to mention 25 all of the possible equivalent forms or ramifications of the invention. It is to be understood that the terms used herein are merely descriptive rather than limiting, and that various changes may be made without departing from the spirit or scope of the invention.
.
FIELD OF T~IE INVENTION
This invention relates to a tactile sensor and a sensing method that can be used to detect contact 5 between the sensor and another object. Some of the properties that can be sensed are shape, texture, pressure, position and orientation. The sensor and sensing method have utility in industrial machinery, robots, medical devices and prosthetic devices.
BACRGROUND OF THE INVENTION
Robotic devices and systems are finding increased usage in a variety of applications. They extend into the realms of medicine (e.g. prosthetic devices), 15 military applications, industrial robots (for assembly), hazardous industrial environments and so on.
For a robotic device to operate intelligently within a given but flexible and changing environment, it must be able to accurately determine, or sense, 20 what its surroundings are. Advanced sensory capabilities will characterize the next generation of robots, and among these sensory functions is tactile sensing, the ability to determine physical features through touch mechanisms. Although the goal can be stated 25 quite simply, the technological implementation presents quite another challenge. Furthermore, the tactile sensing capability is a broad spectrum: at one end of the spectrum is the ability to merely detect the presence of an object, and at the other end is the 30 ability to determine the surface texture of an object.
Rounding out the spectrum is the ability to determine an object's size and shape and whether or not it has moved on the sensor's surface.
An example of a piezoelectric device is U.S. Patent 35 4,328,441 (Kroeger, et al) and its international counter-part WO 81/02223. These reveal a layered structure ~53232 having piezoelectric polymer films on opposite sides of an insulating layer for the purpose of providing a keyboard. This does not avoid the phantom point problem.
IBM Technical Bulletin, Vol. ~0, No. 1, J.P.
Dahl, June 1977, reveals a scanned piezoelectric keyboard switch where each key is chosen to have a uni~ue inherent resonant frequency while the switches are wired in parallel. Contact dampens the f lequency and the imped-10 ance of the undampened crystal changes greatly.
I~M Technical Bulletin, Vol. 20, No. 7, J. Fajans, December 1~77, discloses an acoustical touch panel in which acoustic plane wave impulses are generated at fixed times in orthogonal directions by two long 15 piezoelectric crystals mounted on adjacent sides of a lower plate. ~ocal acoustical coupling is said to result in a spherical wave originating from the point of contact in an upper plate when an impulse is present in the lower plate.
P. Dario et al, "Touch Sensitive Polymer Skin Uses Piezoelectric Prop~rties to Recognize Orientation of Objects", an article in Sensor Review p. 194-198, October 1982, use a single layer polyvinylidene fluoride PVF2 sensor with 256 sensing areas (16 x 16 array) 25 to recognize object orientation. One lead pin is required for each sensing area.
A bilaminate PVF2 sensor is proposed in "Piezo-Pyroelectric Polymers SXin-~ike Tactile Sensors for Robots and Prostheses", 13th Symposium 7 Conference 30 and Ex~osition on Industrial Robots and Robots , Chicago, R. Bardelli et al, April 1983, where the outer layer senses temperature and the inner senses mechanical forces. The article teaches against row by column reading involving multiplexing. A lead for each sensing 35 area is advocated.
In "Piezoelectric Polymers: New Sensor Materials for Robotic Applications", 13th Symposium on Industrial ~;~53~:32 Robots and ~obots 7 Conference and Exposition Chica~, P. Dario et al April 1983, various PVF2 contact sensors and touch sensors are described. The touch sensor using 256 sensor regions has at least 256 leads.
5 A tactile sensor using a PVF2 emitter and receiver uses the time of flight of ultrasonic waves through a compliant material to measure pressure on the sensor.
In the prior art there are several major disadvan-tages that are overcome by the present invention.
10 First the location, shape, and pressure of an object can be actively sensed. Secondly, switching noise problems are overcome by multiplexing the energizing signal rather than the sensing signal. Third, the invention avoids the "phantom point" problem of a 15 crossed array. Fourth, great sensitivity and high resolution are possible. Finally, the complexity of the lead array can be greatly reduced by allowing the use of N + M leads to address N x M active areas.
In accordance with the invention there is provided an apparatus for tactile sensing. One embodiment of the apparatus is basically a sandwich structure of several layers. A first layer of piezoelectric 25 energizing material is used to interrogate the sensing layers. The first layer ma~ have parallel conductors or electrodes on two sides thereof with rows of conductors on one side and columns of conductors on the other.
Other patterns can be used but this pattern was found 30 useful for multiplexing techniques.
An insulating layer separates the piezoelectric energizing layer from a piezoelectric sensing layer that is used as a signal source to detect pressure on the apparatus. The sensing layer may contain two 35 conducting layers on opposing sides of a piezoelectric material. PVF2 is the material of choice for the piezoelectric material for both the energizing and ~2S3~
sensing layerO A base material and outer protective layer, may optionally be a part of the design as well as a multiplexer that is integral with the sensor.
Unlike conventional tactile sensors, this tactile 5 sensor has both a static and dynamic response. When an object contacts the transducer, the sensing layer is flexed, generating a small cutput transient voltage.
However, by continuously AC stimulating areas on the energizing layer (defined by the intersection of one 10 row conductor and one column conductor), an acoustic wave is transmitted through the insulating layer, which in turn stimulates the sensing layer. The output is then a continuous AC signal with a frequency equal to the stimulating frequency and an amplitude correspond-15 ing to the efficiency of acoustic coupling betweenthe layers. When an object comes in contact with the sensor, the acoustic coupling is changed, and the output signal amplitude is consequently changed.
Depending on the frequency of stimulation and the 20 amount of contact force, the acoustic coupling may be dampened or enhanced, and the output signal amplitude is reduced or increased, respectively. By multiplexing the stimulated points on the driving layer--not the signal from the sensing layer--absolute knowledge 25 of when the signal is produced is preserved, without the inherent "dead time" associated with output signal multiplexing. By noting the amplitude of the output signal, the amount of applied force can be determined, and by correlating the multiplexing address to the 30 output signal, the shape of the contacting object can be determined. Even though time multiplexing with row and column addressing was used in the present design, frequency multiplexing can be applied, as well, to obtain the tactile information.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates, in semischematic form, one embodiment of the tactile sensor of the invention.
Figure 2 i]lustrates an embodiment of electrodes ~53~32 used in the energizing layer.
Figure 3 illustrates a top view of one embodiment of the arrangement of conductors of the energizing layer.
Figure 4 illustrates a top view of one embodiment of the superposition of the two layers of electrodes used in the energizing layer.
Figure 5 illustrates one embodiment in semischematic form of the arrangement of various electronic devices 10 to the apparatus of Figure 1.
Figure 6 illustrates in semischematic form another embodiment of the invention wherein two energizing layers are used.
Figure 7 illustrates the typical output characteris-15 tics of the tactile sensor.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENT
_ Figure 1 illustrates one embodiment of the tactile sensor 100. This embodiment comprises a base material 20 101 that is preferably nonresilient. This base surface may be flat or of arbitrary curvature. If desired a resilient material 102 may be placed adjacent to the base material 101; however, this is optional.
An energizing layer 103 is disposed adjacent to the 25 base 101 or optional resilient material 102. Layer 103 is composed of electrodes 105 and 106 on two opposing surfaces of piezoelectric material 104. Electrodes 105,106 may be parallel arrays of electrode bars or conductors as in Figures 1 and 2 or as interconnected 30 discrete pads as shown in Figures 3 and 4. The electrode bars 105,106 are arranged so that they run at right angles and produce an array of surfaces where the surface of one bar is opposite that of another. These surfaces 210,211 stimulate the active site 220. This 35 surface 220 is the active site as explained below and as shown in Figure 2. Adjacent to the electrodes 106 is an insulator 107. Insulator 107 may be composed of an insulatincJ sheet or may be of an insulating adhesive. Preferred embodiment is less than 1/32 ~0 inch latex rubber coated with resilient adhesive on ~:5~3~32 both sides. A second piezoelectric sensing layer 10~ is positioned adjacent to the insulating layer 107. This sensing layer 108 is composed of a piezoelec-tric material 109 with a conductor 110,111 on opposing 5 surfaces. This piezoelectric sensing layer 10~ is preferably resilient. Finally, an optional resilient protective layer 112 may be used to protect the sensor 100 from the environment.
Figure 2 illustrates in an exploded view the 10 arrangement of the energizing layer 103 in greater detail. This layer 103 is composed of a plurality of conductors 105 disposed on one surface of layer 103 and a plurality of conductors 106 on the opposite surface. If conductors 201 and 202 are energized 15 then an energizing area 220 is defined. The energizing area is produced whenever portions of conductors 105,106 are formed at opposing surfaces. Applying an energizing signal to the appropriate conductors through a multiplexer 505 energizes the device.
Figure 3 illustrates a preferred embodiment of one set of electrodes 105,106 of the apparatus. A
typical electrode 300 is constructed of connecting pad 301 and individual electrode pads 302 that define energizing areas 220. E~ternal electrical connection 25 is made to the connection pads 301 and electrode pads 302 by lead connections 303.
Figure 4 illustrates a top view shows a preferred embodiment of one embodiment of electrodes 105,106 as they would be arranged when superimposed on opposite 30 surfaces of piezoelectric energizing layer 104. Thus electrodes 300 are placed at right angles to electrodes 400. The overlaps of two electrode pads 402 defines an energizing area 220.
One of the great advantages of the invention 35 is that the number of electrical connections required is greatly reduced, for a given number of energizing areas. Conversely, for a given number of electrical ~2532:32 connections the number of energi~ing areas is greatly increased. For example, in a rectangular array as iilustrated in Figure 4 where N is the number of connec-tions along the horizontal axis and M is the number 5 of connections along the vertical axis, N ~ M connections allow N x M energizing areas. Thus the particular embodiment shown in Figure 4 where N - 16 and M = 16, 32 connections allow 256 energizing areas.
These energizing areas correspond to sensing 10 areas in the sensing layer. These sensing areas are spatially located on the sensing layer in the same manner as the energizing areas on the energizing layer.
Only pressures located at a point: corresponding to the sensing energizing area will be measured as further 15 discussed below.
The pattern or layout of the conductors and pads may be rectilinear as shown in Figure 1-6 or be in a circular or in any arbitrary shape providing sensing information specific to the desired application.
Figure 5 illustrates one embodiment of the electron-ics associated with the tactile sensor 100. Signal generator 501 is connected to amplifier 503 by leads 502. The amplifier 503 is in turn connected to switching means or multiplexer 505 by leads 504.
Signal input to the tactile sensor apparatus 100 is through electrical connecting leads 506. Leads 506 may be N + M in number where the conductors in the energizing layer are adapted to provide N x M
array of energizing areas 220 in the embodiment of 30 Figure 1. Leads 506 may number an additional P + Q
for an P x Q array in the embodiment of Figure 6 discussed below. The output signal from the sensing layer 108 is directed to amplifier 509 by leads 508. The output of amplifier 509 is sent. to a signal processing means 35 511 by leads 510. Signal processing means 511 converts the information contained in the signal of amplitude and frequency to display and/or control apparatus 513 by leads 51~. Leads 514 and 516 from the signal ~:~53~
processor 511 are optional being required only if the switching means or multiplexer 505 and oscillator 501 are to be controlled by information from the signal processing means 511.
Optionally electrical switching means or multiplexer 505 and leads 506 may be built with the tactile sensor 100 as one unit. This would provide lower wiring complexity and reduce signal interference from other devices. The switching means 505 may be optionally 10 mounted on the base 101 of the apparatus or other suitable place. The oscillator 501 may be fixed or variable in frequency.
In general the apparatus of the invention may be described as comprising a piezoelectric energizing 15 layer 103 having a plurality of conductors 105 disposed on one surface of a piezoelectric material 104 and a plurality of conductors 106 disposed on the opposite surface of the piezoelectric material 104, the plurality of conductors 10~,105 having electrical connections 20 301,401 adapted to be connected to electrical energizing means (not shown); an electrical insulating layer 107 disposed adjacent the piezoelectric energizing layer 103; and a piezoelectric sensing layer 108, having conducting surfaces 110,111 disposed on opposite 25 surfaces thereof, and disposed adjacent the insulating layer 107. Details of the above device include:
conductors in the piezoelectric energizing layer 103 that are to provide N x M energizing areas with N + M
electrical connections to the energizing layer 103, 30 wherein N x M > l; electrical energizing means for driving said energizing layer and electrical processing means for processing signals from the piezoelectric sensing layer 108 and a switching means or multiplexer adapted to be connected to the N + M electrical connec-35 tions and adapted to energize the N x M energizingareas.
~L~53~3~
A further detailed description of the sensor 100 would include: a first electrode layer 105 having N electrodes 201, where N > l; a first piezoelectric polymer layer 104 disposed adjacent to the first electrode 5 layer 105; a second electrode layer 106 having M elec-trodes 202, where M > l; and disposed adjacent to the first piezoelectric polymer layer 104 wherein N x M > l; an insulating layer 107 disposed adjacent to the second electrode layer 106; a first conductive 10 layer 110 disposed adjacent to the insulating layer 107 and adapted to be connected to output processing means; a second piezoelectric polymer layer 109 disposed adjacent to the first conductive layer 110; and a second conductive layer 111 disposed adjacent to the 15 second piezoelectric polymer layer 109 and adapted to be connected to output processing means.
As mentioned previously the apparatus may optionally have a base material 101 which is typically rigid but may have another resilient layer 102 thereon. Like-20 wise a protective layer 112 is disposed adjacent tothe piezoelectric sensing layer. This protective layer 112 must be resilient to transmit forces to the sensing layer 10~.
Figure 6 illustrates another embodiment of the 25 invention wherein an additional piezoelectric energizing layer 603 is added. This embodiment 600 comprises a first electrode layer 605 having N electrodes 201, wherein N > l; a first piezoelectric polymer layer 604 disposed adjacent to the first electrode layer 30 605; a second electrode layer 606 having M electrodes 202, wherein M > 1, and disposed adjacent to the first piezoelectric polymer layer 604; a first insulating layer 607 disposed adjacent to the second electrode layer 606; a third electrode layer 105 having P electrodes 35 201, wherein P > 1, and disposed adjacent to the insulat-ing layer 607; a second piezoelectric polymer layer ~5323~
104 disposed adjacent to the third electrode layer 105; a fourth electrode layer having Q electrodes 202, wherein Q > 1, and disposed adjacent to the second piezoelectric polymer layer 104, wherein P x Q > l;
5 a second insulating layer 107 disposed adjacent to the fourth electrode layer 106; a first conducting layer 110 disposed adjacent to the second insulating layer 107 and adapted to be connected to output signal processing means; a third piezoelectric polymer layer 10 109 disposed adjacent to the first conducting layer 110; and a second conductive layer 111 disposed adjacent to the third piezoelectric polymer 109 and adapted to be connected to output processing means. Optionally, a protective layer 112 may be used as well as a base 15 101 and resilient layer. As can be seen,an additional piezoelectric energizing layer 603 and insulating layer 607 have been added to the basic design of Figure 1 and second electrode layers 605,606 are adapted to provide N x M energizing areas 220 in the first 20 piezoelectric polymer layer 603 with N ~ M electrode connections; and the third and fourth electrode layers 105,106 are adapted to provide P x Q energizing areas 220 in the second piezoelectric layer 103 with P + Q
electrode connections. Switching means or multiplexer 25 505 are connected to the N ~ M and P + Q electrode connections in a manner adapted to energize the appropri-ate N x M and P x Q energizing areas.
Figure 6 may also be described as: a first piezo-electric energizing layer 603 having a plurality of 30 conductors 201 disposed on one surface of a piezoelectric material 604 and a plurality of conductors 202 disposed on the opposite surface of the piezoelectric material 604, the plurality of conductors 201,202 having electrical connections 301,401 adapted to be connected to electrical 35 energizing means; a first electrical insulating layer 607 disposed adjacent the first piezoelectric energizing layer 603; a second piezoelectric energizing layer , ~Z~;~^3Z3~:
103 having a plurality of conductors 201 disposed on one surface of a piezoelectric material 104 and a plurality of conductors 202 disposed on the opposite surface of the piezoelectric material, the plurality 5 of conductors 201,202 having electrical connections 301,402 adapted to be connected to electxical energizing means; second electrical insulating layer 107 disposed adjacent the second piezoelectric energizing layer 103; a piezoelectric sensing layer 108 having conducting 10 surfaces 110;111 disposed on opposite surfaces thereof that is disposed adjacent the second insulating layer 107.
Another embodiment of the invention involves the use of two sensing layers rather than the single 15 sensing layer 108 illustrated in Figures 1 and 6. This additional sensing layer 108' (not illustrated) would be disposed adjacent to the existing piezoelectric sensing layer 108 with an additional insulating layer 107' between them. This additional sensing layer 20 can be used in the embodiments illustrated in Figures 1 and 6. The additional layer would allow a gradation in sensing capability with one layer sensing smaller forces than the other.
This second piezoelectric sensing layer having 25 conducting surfaces on opposite surfaces thereof, and disposed adjacent a second insulating layer may be adapted to have electrical and mechanical character-istics different from the other piezoelectric sensing layer. The layer sensing the lower forces would be 30 preferably placed uppermost in the sensor.
The device is contemplated to operate with variable frequency inputs as further discussed below. D.C.
operation of the energizing layer of the apparatus does not appear practical since the piezoelectric 35 layers have insufficient response to D.C. voltages.
For example, refering to Figure 1, for both D.C. and .
~:~513~:32 A.C. operation the passive and primary sensing ele~ent is the outer most layer of PV~2, layer 108. When an object exerts pressure on the sensor's surface, an output signal is generated. To determine the objects 5 characteristics as for example the shape of the object, single perpendicular pairs of conductors on the first PVF2 layer are energized with a voltage. If the object is not present over the junction of the perpendicular conductors, the second piezoelectric film will simply 10 expand slightly with no consequent output signal.
However, if the object is present, the sensing layer will be compressed and an output signal ~ill be registered.
Thus, by actively interrogating the N x M perpendicular pairs the shape of the object could be determined.
Another limitation of D.C. excitation of the energizing layer is the mechanical coupling between the two PVF2 layers through the insulating film.
If a 30 volt source (+15VDC, standard for many integrated analog circuits) is applied to the perpendicular conductors, 20 this energizing voltage will generate an electric field within the PVF2 film that causes a thickness expansion of approximately ten angstroms (lOA).
In order to accurately transmit this strain to the sensing film, the insulating layer 107 must be either 25 infinitely rigid or be moderately rigid and have thick-nesses on the order of this minute displacement.
Even if the D.C. energizing voltage is increased to, say, 200 V and the displacement increased to 66A, the thickness of the in~ulating material is not practical.
As a result acoustic coupling and an A.C. mode-of energizing operation is preferred.
The device is operated by providing a tactile sensor 100 having a piezoelectric energizing layer 103 with N x M energizing areas 220 and N + M connectors 35 301,401 for the energizing areas 201 and having a piezoelectric sensing layer 108 adjacent to the energizing layer 103 and electrically insulated therefrom; providing a variable frequency electrical signal at a frequency ~L253232 and amplitude adapted to energize the energizing areas 220; switching the signal to the N + M connectors in a manner adapted to energize selected energizing areas 220 of the energizing layer 103 in a predetermined 5 sequence; and processing a signal generated by the sensing layer 108 to determine the characteristics of an object that is touching the sensing layer 111 or protective layer 112. The energizing of selected energizing areas 220 may be in a predetermined sequence 10 in an algorithm driven sequence; in a random se~uence.
An algorithm may be used that provides low spatial resolution and reverts to high resolution when an object is sensed. The method can be adapted to processing a signal from the sensing layer that determines charac-15 teristics of an object touching the device or sensinglayer such as force, shape of the object or ~eight.
The method would be similar for the alternate embodiment of the tactile sensor 601; again one is switching the signal to the connectors 301,401 in 20 a manner adapted to energize selected energizing areas 220 of the energizing layers 103,603 in a predetermined sequence and processing the signal generated by the sensing layer to determine the characteristics of an object touching the sensing layer.
The signal generated in the sensing layer of the tactile sensor apparatus will vary in frequency and amplitude; by processing the frequency and amplitude information in the signal from the sensing layer charac-teristics of an object in contact with the sensor 30 can be determined.
Another method of operation is that of monitoring.
~hile in the monitor mode the energizing layer is inactive. The output of the sensing layer 111 is monitored for a given change in signal. When a signal 35 is detected the energizing system is activated and normal operation resumes. This method may be described in more detail as providing a tactile sensor having ~:53~Z:3;~
a piezoelectric energizing layer with N x M energizing areas and N + M connectors for the energizing areas and having a piezoelectric sensing layer adjacent to the energizing layer and electrically insulated 5 therefrom; providing electrical signal energizing and output processing means; monitoring the electrical output of the sensing layer to determine if an object is in contact with the tactile sensor while keeping the energizing layer and electrical signal energizing 10 means inactive; switching the tactile sensor system to active status when an output s;ignal is sensed from the sensing layer; providing an alternating frequency electrical signal at a frequency and amplitude adapted to energize the energizing areas; switching the signal 15 to the N + M connectors in a manner adapted to energize selected energizing areas of the energizing layer in a predetermined sequence; and processing a signal generated by the sensing layer to determine the charac-teristics of an object that is touching the tactile 20 sensor.
EXAMPLES 1-~
For these examples tests were done at the following forces 0,5,10, and 50g on the sensor.
The sensor was constructed in a ~ inch x ~ inch configuration. A 3/8 inch thick rigid plastic to which was bonded a 1/16 inch thick rigid platform was used for the base material. A 1/32 inch thick latex rubber material was placed over the base. The 30 piezoelectric energizing layer and piezoelectric sènsing layer (~ inch by 1~ inches) were both cut from the same PVF2 stock sheet material. Because of previous problems with separation of metallization on the layers both ~ inch wide strips (approximately 1~ inches long) 35 of metallization PVF2 were cut from a stock sheet so that the grain of metallizatlon/polymer ran parallel to the length of the strips. A 20:1 mixture of polyure-thane adhesive was prepared by adding one small drop ~2~3232 of Tycel*7200 (Lord Corporation) curing agent to .5 ml of T~cel*7000 adhesive. The mixture ~as stirred for about 1 minute and applied to the end of each strip on one side with a brush to lay down a good insulating layer. The adhesive was allowed to dry overnight. A second batch of adhesive was made and applied to one of the previously coated surfaces.
The second strip was laid on top of the first so that the two coated surfaces bonded to each other 10 with an overlap of ~ inch. The :Layers were pressed together and allowed to dry.
Because of heating problems while curing the wire bonding adhesive, the wire leads were first attached to the PVF2 strips before constructing the sensor.
15 Wire-wrap wire was bared approximately 3 mm and laid against the metallized surface near one end of the PVF~ strip. A drop of silver epoxy paste, mixed in a 1:1 ratio was dabbed on this junction and heat cured under a heat lamp for 1~ hours at 80DC. This makes 20 a solid bond with excellent electrical conductivity.
A second wire was attached to each strip on the opposite side near the same end using the same technique.
The finished sensor was then clamped using two insulated paper clips with magnetic bases and stretched 25 across the latex and base above. 0.3 inch x 0.3 inch contact areas were used ~or the weights. Detailed output signal measurements were made for a wide range of stimulation frequencies for the structure unloaded and loaded with 5g, lOg, or 50 grams. The data is 30 plotted in a single graph in Figure 7 so that comparisons can easily be made.
Test Conditions: Input voltage - lOVAC; output voltage bandwidth limited to 20 MHz to reduce the amount of noise content in the signal; load = 0,5,10,50 gm;
35 frequency range: 100 Hz to lOMHz; output voltage measured in mV peak-to-peak (mvpp).
*Trade mark.
~25~23~, This series of tests and the resulting graph of data (Figure 7) reveal considerable information on the tactile models of the device. Clearly, seYeral different trends are seen in terms of response to 5 loading. These are examined below.
First of all, both increased coupling and dampening modes are observed. At 105-110 KHz, a strong resonance is observed with increased monotonic dampening of the output response seen as the loading is increased.
In the frequencies between 2 KHz and 10 KHz, the increased coupling mode is observed for forces above and including 5 gram, while the dampening mode dominates in the 0-5 gram range; hence, the tactile mode is dependent on both frequency and loading.) 15 Two frequency crossover points between coupling and dampening modes are clearly visible. A very sharp crossover occurs at 1.2 KHz where all three loaded data curves intersect at a single point. The second frequency crossover is considerably broader and occurs 20 in the 22KHz-34KHz range.
The second main observation is that frequency shifts in resonance as a function of loading. In the 126-135 Hz range, the first resonance observed, a slight upward shift in resonance correlated with 25 increased force is observed. The same is true for the 105 KHz-llO KHz resonance discussed previously.
However, the most drastic and noteworthy is a shift that begins at 610 Hz under no load and ends up at 370 Hz for a 50 gram load. Not only does the resonant 30 frequency shift, but the amplitude increases dramatlcally.
The table below shows the summary data points of these phenomena:
~;~53~32 l?
Output Amplitude Loadinq (mv pp) Resonant Fre~uency From this response, it is apparent that the loading mass plays an important role in the resonant response of the device ~y moving in harmony with the piezoelectric ~PVF2) structure. Like a vibrating string, the PVF2 10 structure resonates at a frequency that is a function of mass. As the mass increases, the resonant frequency decreases. The increase in amplitude is probably due to increased coupling between the energizing and sensing layers of PVF2.
15 To reiterate, the phenomenon seen here is that the data points for the loaded device show a monotonic relationship at a given frequency. But, the data points for the unloaded device do not necessarily follow the same trend. This is because the response 20 is a function of loading, and the data in Figure 7 includes only loads in 5-50 gram range. In any case, the data presented here indicate strong amplitude and frequency correlations of output signal to loading.
Obviously, by performing a spectral analysis 25 of a wide band of stimulation frequencies, the precise loading could be determined and the range of possible loads may even be broadened. However, to perform such an analysis is expensive and time consuming.
To develop a sensor that responds relatively quickly, 30 say 1-10 msec for the en~ire array, and is not hardware intensive, it is better to examine a single or a few key frequencies rather than the entire spectrum.
The last point to be made concerns capacitive coupling betwee~ the PVF2 layers. This coupling is 35 always present to some extent, however, as the stimulation frequency increases, the coupling increases and eventually 3~5~3~
dominates the system so that no tactile response is observed.
In our test conditions, the coupling effect was noticeable around 300 KHz, was definitely dominating 5 the data at 700 KHz, and was the only signal observed at 900 KHz. In fact, for stimulation frequencies of 900 KHz and above, there were no observable diferences in the output signal level for various loadings. And as expected, as capacitive coupling increased, so 10 did the output signal level.
Thus, in general, the PVF2 structure must be stimulated with a signal whose frequency is well below the point where capacitive coupling interferes with the tactile response signal.
To further document the invention the oscilloscope signals for the sensor configuration used in Examples 1-4 were monitored.
The dampening mode tactile response was distinctly evident and apparent for the range of loads from 0 to 50 grams. The change in output voltage is a non-linear function of loading, but nonetheless, it is strongly correlated to the loading.
~5 A phase shift phenomenon was also observed.
This characteristic has been observed by other researchers investigating the tactile response of PVF2. The amount of phase shift may be correlated to the time of travel for an acoustic signal to propagate across the flexible 30 adhesive layer. As loading is applied to the structur~, the device becomes more tightly pressed, and the distance bet~een the PVF2 layers ~ecomes less. Thus, the time to travel and the phase shift becomes less.
The response to a sinusoidal input at resonance 35 (105 KHz) shows the dampening mode response and a sensitivity to :loads as small as one gram. Although ~;~5;~232 the change in output amplitude as a function of loading is not linear, the two parameters are correlated.
The response of the sensor to a 10 K~z square wave input was tested. This frequency was chosen because this frequency lies in the region where previously the unloaded response did not appear to correlate to the ~rend established by the loaded (5, 10, and 10 50 g) response data.
The most obvious response to the square wave input is the characteristic piezoelectric response of a decaying sinusoid, which begins with a sharp spike in response to the step stimulation and exponen-15 tially decays. Superimposed on the exponential decayis resonant ringing. As expected, the resonance was observed to ring at approximately 100 KHz.
As the device was loaded under this stimulation condition, two important changes were observed in 20 the output. First, the resonant spike and ringing continuously decreased as the loading increased.
This was expected from the data in Figure 7. More importantly, the low frequency (10 KHz) response, was also affected.
~or small loading (up to 5 grams), the load dampened the output response. The output resembled a square wave, with the amplitude decreased with increasing loading until at approximately 5 grams only the resonant response could be seen. The amplitude of the low frequency 30 stimulation and response had practically vanished.
As the loading continued to increase, an interesting reversal took place, and the output began to resemble a square wave in phase with the input. Thus, the increased coupling mode began to dominate the system, and the 35 output signal increased with loading. For 30 g loading, the resonant ringing had almost disappeared, and the low frequency response was similar to the input.
~L~25~;232 The total response to loading shows a smooth drop from 12 mvpp to zero in square wave output for the load range 0-5 grams followed by an increase in output signal to an asymptote at approximately 5 ~Ivpp. We 5 have chosen to call the force applied when minimum signal output is observed the loacl crossover point.
The load crossover point bet~een the increased coupling mode and the dampening mode is approximately 4~ grams of loading for the 10 KMz square wave. This 10 crossover point shifts up or down depending on the stimulation frequency. For example, at 100 XHz -105 KHz the crossover point has shifted upward to an undetermined point so that only the dampening mode is seen for loads in the 0 - 50 gram range.
One useful application of this frequency-dependent response is the incorporation of multiple sampling frequencies to dynamically change sensitivity without changing geometry or to verify a response at one frequency by correlation of the response at another frequency, 20 hence increasing the sensor's accuracy.
A preferred bonding or adhesive materia for the tactile sensor is Tycel ~ 7300 urethane laminating adhesive combined with 7200 Series curing agent in a ratio of 20:1 adhesive to curing agent (Hughson 25 Chemicals, Lord Corporation, 2000 West Grandview Blvd., Erie, Pennsylvania 16512~. Of course any material of similar characteristics can also be used. This nonconducting material is resilient and is used for bonding the various layers of the sensor together.
30 The above adhesive had the appropriate bonding qualities necessary to bond the various layers of the sensor to each other while simultaneously providing good acoustic coupling between the layers. It is essential that each of the layers of the tactile sensor be properly 35 bonded to the adjacent layers to provide good acoustic coupling between layers.
~;253232 A preferred embodiment for the insulators (e.g.
107) is a very thin layer of less than 1/32 inch thickness latex rubber coated with a resilient adhesive.
As mentioned earlier the piezoelectric layers 5 are preferably a piezoelectric polymer such as PVF2 and are in the form of a thin film the electrodes being formed or etched thereon on in ways generally known in the art. Preferably the electrodes are v~por deposited.
Electrical contact to the electrodes or conductors of the piezoelectric sensing and energizing layers is preferably with a silver epoxy although other materials known in the art may be used. An example of preferred electrical conducting epoxy is EPO-TEK~ H20E (Epoxy 15 Technology Inc., 14 Fortune Drive, Billerica, Massachusetts 01821~ although any similar silver filled epoxy such as those designed for chip bonding in microelectronic and optoelectronic applications may be used. The H20E epoxy used requires heat treatment; thus, temperature 20 should be kept below the temperature where the piezoelec-tric material would lose its electrical polarization.
For PVF2 this temperature should be below 120C.
A temperature of 80C was found to be suitable.
The leads are preferably attached to the piezoelec-25 tric layers of the sensor prior to assembly with the nonconducting adhesive used to hold the various layers together. This allows subsequent assembly steps at room temperature and avoids elevated temperatures that would affect the nonconducting adhesive.
As mentioned previously polyvinylidene fluoride (PVF2) is the prererred piezoelectric material. It should have its electrical polarization oriented in the thickness direction. Preferred thickness of the piezoelectric material using PVF2 is approximately 35 28~m. This is a medium size thickness that optimizes the motor and generator responses (mechanical reaction to electrical stimulus and electrical reaction to mechanical stim~lus) of PVF2. Other usable thicknesses ~ZS323:2 range from a few micrometers to as large as several millimeters.
Input voltages to the energi2ing electrical energiz-ing layer 103 of the tactile sensor lOO by an oscillator 5 501 may be fixed, variable, sinusoidal square or a suitable arbitrary wave form of single or multiple frequencies. A square wave of lK~Iz-lOKHz was ~ound to provide adequate information about the sensor response at the ~undamental frequency and higher harmonics lO and to provide adequate information for ambiguously identifying the force applied to the tactile sensor from an unknown load.
The invention solves another problem common to cross point arrays--the phantom point. For example 15 in an N = 2 by M = 2 array of conductors there are N x M = 4 points. If however three of these points are energized simultaneously the fourth point cannot be determined to be on or off. Output signals would be the same in either case. The invention avoids 20 this problem by addressing each point independently in time by the switching means or multiplexer 505.
While the forms of the invention herein disclosed constitute presently preferred embodiments, many others are possible. It is not intended herein to mention 25 all of the possible equivalent forms or ramifications of the invention. It is to be understood that the terms used herein are merely descriptive rather than limiting, and that various changes may be made without departing from the spirit or scope of the invention.
.
Claims (60)
1. A tactile sensing apparatus comprising:
a. a piezoelectric energizing layer having a plurality of conductors disposed on one surface of a piezoelectric material and a plurality of conductors disposed on the opposite surface of the piezoelectric material, the plurality of conductors having electrical connections adapted to be connected to electrical energizing means;
b. an electrical insulating layer disposed adjacent the piezoelectric energizing layer;
and c. a piezoelectric sensing layer, having conducting surfaces disposed on opposite surfaces thereof, and disposed adjacent the insulating layer.
a. a piezoelectric energizing layer having a plurality of conductors disposed on one surface of a piezoelectric material and a plurality of conductors disposed on the opposite surface of the piezoelectric material, the plurality of conductors having electrical connections adapted to be connected to electrical energizing means;
b. an electrical insulating layer disposed adjacent the piezoelectric energizing layer;
and c. a piezoelectric sensing layer, having conducting surfaces disposed on opposite surfaces thereof, and disposed adjacent the insulating layer.
2. The apparatus of Claim 1 further comprising a protective layer disposed adjacent to the piezoelectric sensing layer.
3. The apparatus of Claim 1 wherein the conductors in the piezoelectric energizing layer are adapted to provide N x M energizing areas with N + M electrical connections to the energizing layer wherein N x M > 1.
4. The apparatus of Claim 3 further comprising electrical energizing means for driving the energizing layer and electrical processing means for processing signals from the piezoelectric sensing layer.
5. The apparatus of Claim 4 wherein the electrical energizing means further comprises:
a. a variable frequency oscillator;
b. an amplifier coupled to the oscillator;
c. a multiplexer coupled to the amplifier and coupled to the energizing layer; and d. a signal processor coupled to the variable frequency oscillator and multiplexer; and wherein the electrical processing means further comprises an output amplifier coupled to the signal processor that is in turn coupled to signal output means.
a. a variable frequency oscillator;
b. an amplifier coupled to the oscillator;
c. a multiplexer coupled to the amplifier and coupled to the energizing layer; and d. a signal processor coupled to the variable frequency oscillator and multiplexer; and wherein the electrical processing means further comprises an output amplifier coupled to the signal processor that is in turn coupled to signal output means.
6. The apparatus of Claim 3 further comprising a multiplexer adapted to be connected to the N + M
electrical connections and adapted to energize the N x M energizing areas.
electrical connections and adapted to energize the N x M energizing areas.
7. The apparatus of Claim 6 further comprising electrical energizing means adapted to energizing the multiplexer and electrical processing means adapted to processing signals from the piezoelectric sensing layer.
8. The apparatus of Claim 7 wherein the electrical energizing means further comprises: a variable frequency oscillator coupled to the multiplexer and a signal processor; and wherein the electrical processing means further comprises the signal processor coupled to the piezoelectric sensing layer.
9. The apparatus of Claim 7 wherein the electrical energizing means further comprises an oscillator and wherein the electrical processing means comprises a signal processor.
10. The apparatus of Claim 9 wherein the oscillator is a variable frequency oscillator.
11. The apparatus of Claim 1 wherein the piezoelec-tric material is PVF2.
12. A tactile sensing apparatus comprising:
a. a base material;
b. a piezoelectric energizing layer disposed on the base material having a plurality of conductors disposed on one surface of a piezoelectric material and a plurality of conductors disposed on the opposite surface on the piezoelectric material, the plurality of conductors having electrical connections adapted to be connected to electrical switching means;
c. an electrical insulating layer disposed adjacent the energizing layer; and d. a piezoelectric sensing layer, having conducting surfaces disposed on opposite surfaces thereof, and disposed adjacent the insulating layer, the conducting surfaces adapted to be connected to electrical processing means.
a. a base material;
b. a piezoelectric energizing layer disposed on the base material having a plurality of conductors disposed on one surface of a piezoelectric material and a plurality of conductors disposed on the opposite surface on the piezoelectric material, the plurality of conductors having electrical connections adapted to be connected to electrical switching means;
c. an electrical insulating layer disposed adjacent the energizing layer; and d. a piezoelectric sensing layer, having conducting surfaces disposed on opposite surfaces thereof, and disposed adjacent the insulating layer, the conducting surfaces adapted to be connected to electrical processing means.
13. The apparatus of Claim 12 further comprising a protective layer disposed adjacent to the piezoelectric sensing layer.
14. The apparatus of Claim 12 wherein the conductors in the piezoelectric energizing layer are adapted to provide N x M energizing areas with N + M electrical connections to the energizing layer wherein N x M > 1.
15. The apparatus of Claim 12 further comprising:
a. electrical energizing means for energizing the piezoelectric energizing layer; and b. electrical processing means for processing signals from the piezoelectric sensing layer.
a. electrical energizing means for energizing the piezoelectric energizing layer; and b. electrical processing means for processing signals from the piezoelectric sensing layer.
16. The apparatus of Claim 12 wherein a piezoelec-tric material disposed in the piezoelectric energizing and sensing layer further comprises PVF2.
17. The apparatus of Claim 12 further comprising a resilient material between the base material and piezoelectric energizing layer.
18. The apparatus of Claim 12 further comprising electrical switching means connected to the N + M
electrode connections and disposed on the base material.
electrode connections and disposed on the base material.
19. The apparatus of Claim 15 wherein the electrical energizing means further comprises an oscillator.
20. The apparatus of Claim 18 wherein the electrical switching means comprises a multiplexer.
21. The apparatus of Claim 19 wherein the oscillator further comprises a variable frequency oscillator.
22. A tactile sensing apparatus comprising:
a. a first electrode layer having N electrodes, where N ? 1;
b. a first piezoelectric layer disposed adjacent to the first electrode layer;
c. a second electrode layer having M electrodes, where M > l, and disposed adjacent to the first piezoelectric polymer layer wherein N x M > 1;
d. an insulating layer disposed adjacent to the second electrode layer;
e. a first conductive layer disposed adjacent to the insulating layer and adapted to be connected to output processing means;
f. a second piezoelectric layer disposed adjacent to the first conductive layer; and g. a second conductive layer disposed adjacent to the second piezoelectric layer and adapted to be connected to output processing means.
a. a first electrode layer having N electrodes, where N ? 1;
b. a first piezoelectric layer disposed adjacent to the first electrode layer;
c. a second electrode layer having M electrodes, where M > l, and disposed adjacent to the first piezoelectric polymer layer wherein N x M > 1;
d. an insulating layer disposed adjacent to the second electrode layer;
e. a first conductive layer disposed adjacent to the insulating layer and adapted to be connected to output processing means;
f. a second piezoelectric layer disposed adjacent to the first conductive layer; and g. a second conductive layer disposed adjacent to the second piezoelectric layer and adapted to be connected to output processing means.
23. The apparatus of Claim 22 further comprising a protective layer disposed adjacent to the second conductive layer.
24. The apparatus of Claim 22 further comprising a base layer disposed adjacent to the first electrode layer.
25. The apparatus of Claim 24 further comprising a protective layer disposed adjacent to the second conductive layer.
26. The apparatus of Claim 22 wherein the first electrode layer and second electrode layer are adapted to provide N x M energizing areas in the first piezoelec-tric layer with N + M electrode connections.
27. The apparatus of Claim 23 wherein the first electrode layer and second electrode layer are adapted to provide N x M energizing areas in the first piezoelec-tric layer with N + M electrode connections.
28. The apparatus of Claim 24 wherein the first electrode layer and second electrode layer are adapted to provide N x M energizing areas in the first piezoelec-tric layer with N + M electrode connections.
29. The apparatus of Claim 35 wherein the first electrode layer and second electrode layer are adapted to provide N x M energizing areas in the first piezoelec-tric layer with N + M electrode connections.
30. The apparatus of Claim 26 wherein the piezoelec-tric layer comprises PVF2.
31. The apparatus of Claim 26 further comprising electrical switching means connected to the N + M
electrical connections in a manner adapted to energize the N x M energizing areas.
electrical connections in a manner adapted to energize the N x M energizing areas.
32. The apparatus of Claim 29 further comprising electrical switching means connected to the N + M
electrical connections in a manner adapted to energize the N x M energizing areas and disposed on the base material.
electrical connections in a manner adapted to energize the N x M energizing areas and disposed on the base material.
33. The apparatus of Claim 26 further comprising:
a. electrical energizing means for energizing the energizing areas through the N and M electrodes;
and b. electrical output processing means for processing signals from the first and second conductive layers.
a. electrical energizing means for energizing the energizing areas through the N and M electrodes;
and b. electrical output processing means for processing signals from the first and second conductive layers.
34. The apparatus of Claim 31 further comprising:
a. electrical energizing means for energizing the energizing areas connected to the multiplexer;
and b. electrical output processing means for processing signals from the first and second conductive layers.
a. electrical energizing means for energizing the energizing areas connected to the multiplexer;
and b. electrical output processing means for processing signals from the first and second conductive layers.
35. The apparatus of Claim 34 wherein the electrical energizing means comprises an oscillator.
36. A tactile sensing apparatus comprising:
a. a first piezoelectric energizing layer having a plurality of conductors disposed on one surface of a piezoelectric material and a plurality of conductors disposed on the opposite surface of the piezoelectric material, the plurality of conductors having electrical connections adapted to be connected to electrical energizing means;
b. a first electrical insulating layer disposed adjacent the first piezoelectric energizing layer;
c. a second piezoelectric energizing layer having a plurality of conductors disposed on one surface of a piezoelectric material and a plurality of conductors disposed on the opposite surface of the piezoelectric material, the plurality of conductors having electrical connections adapted to be connected to electrical energizing means;
d. a second electrical insulating layer disposed adjacent the second piezoelectric energizing layer; and e. a piezoelectric sensing layer having conducting surfaces disposed on opposite surfaces thereof that is disposed adjacent the second insulating layer.
a. a first piezoelectric energizing layer having a plurality of conductors disposed on one surface of a piezoelectric material and a plurality of conductors disposed on the opposite surface of the piezoelectric material, the plurality of conductors having electrical connections adapted to be connected to electrical energizing means;
b. a first electrical insulating layer disposed adjacent the first piezoelectric energizing layer;
c. a second piezoelectric energizing layer having a plurality of conductors disposed on one surface of a piezoelectric material and a plurality of conductors disposed on the opposite surface of the piezoelectric material, the plurality of conductors having electrical connections adapted to be connected to electrical energizing means;
d. a second electrical insulating layer disposed adjacent the second piezoelectric energizing layer; and e. a piezoelectric sensing layer having conducting surfaces disposed on opposite surfaces thereof that is disposed adjacent the second insulating layer.
37. The apparatus of Claim 36 further comprising a base material disposed adjacent the first piezoelectric energizing layer.
38. The apparatus of Claim 37 further comprising a protective layer disposed adjacent to the piezoelectric sensing layer.
39. The apparatus of Claim 36 wherein the conductors are adapted to provide N x M energizing areas with N + M electrical connections to the conductors wherein N x M ? 1 in the first piezoelectric layer and P x Q
energizing areas in the second piezoelectric energizing layer with P + Q electrical connections wherein P x Q ? 1.
energizing areas in the second piezoelectric energizing layer with P + Q electrical connections wherein P x Q ? 1.
40. The apparatus of Claim 39 further comprising switching means connected to the N + M and P + Q electri-cal connections in a manner adapted to energize the appropriate N x M and P x Q energizing areas.
41. A tactile sensing apparatus comprising:
a. a first electrode layer having N electrodes, wherein N ? 1;
b. a first piezoelectric polymer layer disposed adjacent to the first electrode layer;
c. a second electrode layer having M electrodes, wherein M ? 1, and disposed adjacent to the first piezoelectric polymer layer, wherein N x M ? 1;
d. a first insulating layer disposed adjacent to the second electrode layer;
e. a third electrode layer having P electrodes, wherein P ? 1, and disposed adjacent to the insulat-ing layer;
f. a second piezoelectric polymer layer disposed adjacent to the third electrode layer;
g. a fourth electrode layer having Q electrodes, wherein Q ? 1, and disposed adjacent to the second piezoelectric polymer layer, wherein P x Q > 1;
h. a second insulating layer disposed adjacent to the fourth electrode layer;
i. a first conducting layer disposed adjacent to the second insulating layer and adapted to be connected to output signal processing means;
j. a third piezoelectric polymer layer disposed adjacent to the first conducting layer;
and k. a second conductive layer disposed adjacent to the third piezoelectric polymer and adapted to be connected to output processing means.
a. a first electrode layer having N electrodes, wherein N ? 1;
b. a first piezoelectric polymer layer disposed adjacent to the first electrode layer;
c. a second electrode layer having M electrodes, wherein M ? 1, and disposed adjacent to the first piezoelectric polymer layer, wherein N x M ? 1;
d. a first insulating layer disposed adjacent to the second electrode layer;
e. a third electrode layer having P electrodes, wherein P ? 1, and disposed adjacent to the insulat-ing layer;
f. a second piezoelectric polymer layer disposed adjacent to the third electrode layer;
g. a fourth electrode layer having Q electrodes, wherein Q ? 1, and disposed adjacent to the second piezoelectric polymer layer, wherein P x Q > 1;
h. a second insulating layer disposed adjacent to the fourth electrode layer;
i. a first conducting layer disposed adjacent to the second insulating layer and adapted to be connected to output signal processing means;
j. a third piezoelectric polymer layer disposed adjacent to the first conducting layer;
and k. a second conductive layer disposed adjacent to the third piezoelectric polymer and adapted to be connected to output processing means.
42. The apparatus of Claim 41 wherein the first and second electrode layers are adapted to provide N x M energizing areas in the first piezoelectric polymer film layer with N + M electrode connections;
and wherein the third and fourth electrode layers are adapted to provide P x Q energizing areas in the second piezoelectric film layer with P + Q electrode connections.
and wherein the third and fourth electrode layers are adapted to provide P x Q energizing areas in the second piezoelectric film layer with P + Q electrode connections.
43. The apparatus of Claim 42 further comprising switching means connected to the N + M and P + Q electrode connections in a manner adapted to energize the appropri-ate N x M and P x Q energizing areas.
44. The apparatus of Claim 42 wherein the switching means comprises a multiplexer.
45. The apparatus of Claim 42 further comprising a first multiplexer connected to the N + M electrode connections and a second multiplexer connected to the P + Q electrode connections each adapted to respec-tively energize the N x M and P x Q energizing areas.
46. The apparatus of Claim 1 further comprising:
a. an electrical insulating layer disposed adjacent the piezoelectric sensing layer; and b. a second piezoelectric sensing layer, having conducting surfaces on opposite surface thereof, and disposed adjacent the second insulating layer and wherein the second piezoelectric sensing layer is adapted to have electrical and mechanical characteristics different from the other piezoelec-tric sensing layer.
a. an electrical insulating layer disposed adjacent the piezoelectric sensing layer; and b. a second piezoelectric sensing layer, having conducting surfaces on opposite surface thereof, and disposed adjacent the second insulating layer and wherein the second piezoelectric sensing layer is adapted to have electrical and mechanical characteristics different from the other piezoelec-tric sensing layer.
47. The apparatus of Claim 22 further comprising:
a. a second insulating layer disposed adjacent to the second conductive layer;
b. a third conductive layer disposed adjacent to the second insulating layer and adapted to be connected to output processing means;
c. a third piezoelectric polymer layer disposed adjacent to the third conductive layer;
and d. a fourth conductive layer disposed adjacent to the third piezoelectric polymer layer and adapted to be connected to output processing means.
a. a second insulating layer disposed adjacent to the second conductive layer;
b. a third conductive layer disposed adjacent to the second insulating layer and adapted to be connected to output processing means;
c. a third piezoelectric polymer layer disposed adjacent to the third conductive layer;
and d. a fourth conductive layer disposed adjacent to the third piezoelectric polymer layer and adapted to be connected to output processing means.
48. The apparatus of Claim 47 wherein the second and third piezoelectric layers are adapted to have different electrical and mechanical characteristics.
49. The apparatus of Claim 41 further comprising:
a. a third insulating layer disposed adjacent to the second conducting layer;
b. a third conducting layer disposed adjacent to the third insulating layer and adapted to be connected to output signal processing means;
c. a fourth piezoelectric polymer layer disposed adjacent to the third conducting layer;
and d. a fourth conducting layer disposed adjacent to the fourth piezoelectric polymer layer and adapted to be connected to signal processing means.
a. a third insulating layer disposed adjacent to the second conducting layer;
b. a third conducting layer disposed adjacent to the third insulating layer and adapted to be connected to output signal processing means;
c. a fourth piezoelectric polymer layer disposed adjacent to the third conducting layer;
and d. a fourth conducting layer disposed adjacent to the fourth piezoelectric polymer layer and adapted to be connected to signal processing means.
50. The apparatus of Claim 49 wherein the third and fourth piezoelectric layers are adapted to have different electrical and mechanical characteristics.
51. A method of operating a tactile sensor comprising:
a. providing a tactile sensor having a piezoelectric energizing layer with N x M energizing areas and N + M connectors for the energizing areas and having a piezoelectric sensing layer adjacent to the energizing layer and electrically insulated therefrom;
b. providing an alternating frequency electri-cal signal at a frequency and amplitude adapted to energize the energizing areas;
c. switching the signal to the N + M connectors in a manner adapted to energize selected energizing areas or the energizing layer in a predetermined sequence; and d. processing a signal generated by the sensing layer to determine the characteristics of an object that is touching the sensing layer.
a. providing a tactile sensor having a piezoelectric energizing layer with N x M energizing areas and N + M connectors for the energizing areas and having a piezoelectric sensing layer adjacent to the energizing layer and electrically insulated therefrom;
b. providing an alternating frequency electri-cal signal at a frequency and amplitude adapted to energize the energizing areas;
c. switching the signal to the N + M connectors in a manner adapted to energize selected energizing areas or the energizing layer in a predetermined sequence; and d. processing a signal generated by the sensing layer to determine the characteristics of an object that is touching the sensing layer.
52. The method of Claim 51 whereby the energizing of selected areas in a predetermined sequence is in an algorithm driven sequence.
53. The method of Claim 51 whereby the energizing of selected areas in a predetermined sequence is in a random sequence.
54. The method of Claim 51 whereby the energizing of selected areas in a predetermined sequence is by an algorithm that provides low spatial resolution and reverts to high resolution when an object is sensed.
55. A method of Claim 51 whereby the processing of a signal from the sensing layer is adapted to determine force on the sensing layer.
56. The method of Claim 51 whereby the processing of a signal from the sensing layer is adapted to determine the shape of an object touching the sensing layer.
57. A method of operating a tactile sensor comprising:
a. providing a tactile sensor having a first and second piezoelectric energizing layer with N x M energizing areas and N + M connectors on the first layer and P x Q energizing areas and P + Q connectors on the second layer, further having a piezoelectric sensing layer disposed adjacent to the second energizing layer and electri-cally insulated therefrom;
b. providing an alternating frequency electri-cal signal at a frequency and amplitude adapted to energize the M x N and P x Q energizing areas;
c. switching the signal to the connectors in a manner adapted to energize selected energizing areas of the energizing layer in a predetermined sequence; and d. processing a signal generated by the sensing layer to determine the characteristics of an object touching the sensing layer.
a. providing a tactile sensor having a first and second piezoelectric energizing layer with N x M energizing areas and N + M connectors on the first layer and P x Q energizing areas and P + Q connectors on the second layer, further having a piezoelectric sensing layer disposed adjacent to the second energizing layer and electri-cally insulated therefrom;
b. providing an alternating frequency electri-cal signal at a frequency and amplitude adapted to energize the M x N and P x Q energizing areas;
c. switching the signal to the connectors in a manner adapted to energize selected energizing areas of the energizing layer in a predetermined sequence; and d. processing a signal generated by the sensing layer to determine the characteristics of an object touching the sensing layer.
58. A method of operating a tactile sensor comprising:
a. providing a tactile sensor having a piezoelectric energizing layer with N x M energizing areas and N + M connectors for the energizing areas and having a piezoelectric sensing layer adjacent to the energizing layer and electrically insulated therefrom;
b. providing a variable frequency electrical signal at a frequency and amplitude adapted to energize the energizing areas;
c. switching the signal to the connectors in a manner adapted to energize selected energizing areas of the energizing layer in a predetermined sequence;
d. generating a signal in the sensing layer that varies in frequency, amplitude, in response to an object in contact with the tactile sensor;
and e. processing the frequency and amplitude information in the signal from the sensing layer to determine the characteristics of the object.
a. providing a tactile sensor having a piezoelectric energizing layer with N x M energizing areas and N + M connectors for the energizing areas and having a piezoelectric sensing layer adjacent to the energizing layer and electrically insulated therefrom;
b. providing a variable frequency electrical signal at a frequency and amplitude adapted to energize the energizing areas;
c. switching the signal to the connectors in a manner adapted to energize selected energizing areas of the energizing layer in a predetermined sequence;
d. generating a signal in the sensing layer that varies in frequency, amplitude, in response to an object in contact with the tactile sensor;
and e. processing the frequency and amplitude information in the signal from the sensing layer to determine the characteristics of the object.
59. A method of operating a tactile sensor comprising:
a. providing a tactile sensor having a piezoelectric energizing layer with N x M energizing areas and N + M connectors for the energizing areas and having a piezoelectric sensing layer adjacent to the energizing layer and electrically insulated therefrom;
b. providing a variable frequency electrical signal at a frequency and amplitude adapted to energize the energizing areas;
c. switching the signal to the connectors in a manner adapted to energize selected energizing areas of the energizing layer in a predetermined sequence and in a manner adapted to eliminate the phantom point problem;
d. generating a signal in the sensing layer that varies in frequency and amplitude in response to an object in contact with the tactile sensor;
and e. processing the signal from the sensing layer to determine characteristics of the object.
a. providing a tactile sensor having a piezoelectric energizing layer with N x M energizing areas and N + M connectors for the energizing areas and having a piezoelectric sensing layer adjacent to the energizing layer and electrically insulated therefrom;
b. providing a variable frequency electrical signal at a frequency and amplitude adapted to energize the energizing areas;
c. switching the signal to the connectors in a manner adapted to energize selected energizing areas of the energizing layer in a predetermined sequence and in a manner adapted to eliminate the phantom point problem;
d. generating a signal in the sensing layer that varies in frequency and amplitude in response to an object in contact with the tactile sensor;
and e. processing the signal from the sensing layer to determine characteristics of the object.
60. A method of operating a tactile sensor system comprising:
a. providing a tactile sensor having a piezoelectric energizing layer with N x M energizing areas and N + M connectors for the energizing areas and having a piezoelectric sensing layer adjacent to the energizing layer and electrically insulated therefrom;
b. providing electrical signal energizing and output processing means;
c. monitoring the electrical output of the sensing layer to determine if an object is in contact with the tactile sensor while keeping the energizing layer and electrical signal energizing means inactive;
d. switching the tactile sensor system to active status when an output signal is sensed from the sensing layer;
e. providing an alternating frequency electri-cal signal at a frequency and amplitude adapted to energize the energizing areas;
f. switching the signal to the N + M connectors in a manner adapted to energize selected energizing areas of the energizing layer in a predetermined sequence; and g. processing a signal generated by the sensing layer to determine the characteristics of an object that is touching the tactile sensor.
a. providing a tactile sensor having a piezoelectric energizing layer with N x M energizing areas and N + M connectors for the energizing areas and having a piezoelectric sensing layer adjacent to the energizing layer and electrically insulated therefrom;
b. providing electrical signal energizing and output processing means;
c. monitoring the electrical output of the sensing layer to determine if an object is in contact with the tactile sensor while keeping the energizing layer and electrical signal energizing means inactive;
d. switching the tactile sensor system to active status when an output signal is sensed from the sensing layer;
e. providing an alternating frequency electri-cal signal at a frequency and amplitude adapted to energize the energizing areas;
f. switching the signal to the N + M connectors in a manner adapted to energize selected energizing areas of the energizing layer in a predetermined sequence; and g. processing a signal generated by the sensing layer to determine the characteristics of an object that is touching the tactile sensor.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000502531A CA1253232A (en) | 1986-02-24 | 1986-02-24 | Active tactile sensor apparatus and method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000502531A CA1253232A (en) | 1986-02-24 | 1986-02-24 | Active tactile sensor apparatus and method |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1253232A true CA1253232A (en) | 1989-04-25 |
Family
ID=4132531
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000502531A Expired CA1253232A (en) | 1986-02-24 | 1986-02-24 | Active tactile sensor apparatus and method |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1253232A (en) |
-
1986
- 1986-02-24 CA CA000502531A patent/CA1253232A/en not_active Expired
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