PATENT ABSTRACT
A synthetic nervous system ( 10 ) capable of rudimental learning and self-organization for robotic applications having a control circuit ( 190 ) and servo actuators ( 224 ) using oscillating continuously variable analog voltages to mimic natural bio-neural processes. Simple oscillators ( 1 - 8 ) capable of being modulated in frequency, phase, amplitude, and DC offset act as analog processing elements or oscillating infinite state machines. A central pattern generator ( 140 ) utilizing periodic, quasi-periodic, or chaotic oscillators or phase shifters, or a combination thereof, along with a basic motor neuron circuit ( 314 ) enables multiple servos to coordinate their behavior to enable bio-inspired locomotion such as walking, swimming, flapping, crawling, and the like. Sensors ( 200 ) interfaced to the control circuit ( 190 ) provide a wide range of adaptive behavior such as following a light source, avoiding an obstacle, and shifting balance point. Overlapping or concurrent sensor input can provide complex behavior with minimal circuitry.

PATENT DESCRIPTION
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention is directed to robotic control systems and, more particularly, to analog circuitry that simulates natural neurons, including a central pattern generator utilizing the multiple domains of frequency, phase, amplitude, and DC offset, and to a continuously variable analog synthetic nervous system.  
         [0003]     2. Description of the Related Art  
         [0004]     Robotic designs attempt to simulate the movement patterns of animals. With the exception of some lower invertebrates, animals have a nervous network that utilizes a central pattern generator to coordinate and synchronize the movements of their muscles. The central pattern generator has a pacemaker neuron functioning as a simple oscillator that does not require an input. The pacemaker neuron, when combined with a phase shifting network or interacting pacemaker neurons, causes the generation of an oscillating signal that is received at the muscle tissue through inter-neurons and motor neurons. In the time domain, these neurons communicate via voltage spikes. In other words, output voltage pulses are generated that can be measured in cycles per second.  
         [0005]     This form of communication can be effective and robust, especially in the noisy environment where signal attenuation may occur over a long distance, e.g., from the spinal cord to a human hand.  
         [0006]     A substantial amount of research has taken place in this field with respect to robotics and artificial life. This research and its resulting applications tends to be not only complex but also expensive. Very complex circuits using custom silicon and digital signal processors have been created to simulate how a natural central processing generator and nervous system work. Others have attempted to create simple nervous network systems for robots. One example is found in U.S. Pat. No. 5,325,031 issued to Tilden on Jun. 28, 1994. Tilden describes an adaptive robotic nervous system and control circuit for use with a limbed robot that utilizes a reconfigurable central network oscillator to sequence the processes of the robotic legs, each of which is itself autonomous. A pulse delay circuit is provided that, when connected to a second pulse delay circuit, acts as an artificial neuron. The device of Tilden suffers from several disadvantages, one of which is that the actuated limb has no way of detecting where it is in its phase space, and hence it limits feedback control beyond motor power consumption. In addition, Tilden utilizes Schmidt triggers in the central pattern oscillator that fire at one voltage and reset at a lower voltage to give a digital output, thus failing to take full advantage of the benefits of analog circuitry.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     The disclosed embodiments of the invention are directed to robotic systems, and particularly to control circuits for robotic systems utilizing a basic motor neuron circuit that synthesizes all forms of limbed, finned, and undulating robotic locomotion. In one embodiment, an oscillating infinite state machine approach is used wherein analog circuits utilizing off-the-shelf servo motors, particularly those used in radio controlled aircraft and model cars, provide a simplified and cost-effective method for controlling locomotion and other robotic movement.  
         [0008]     More specifically, in one embodiment of the invention analog electronic circuitry is provided that includes a plurality of basic motor neuron circuits controlled by a central pattern generator circuit to provide a continuously variable analog voltage. This voltage enables multiple motor neurons to coordinate their behavior and allow such robotic activities as walking, swimming, flapping, crawling, etc. By interfacing sensors to the synthetic nervous system, a wide range of adaptive behavior can be simulated by the robot, e.g., following a light, avoiding an obstacle, shifting a balance point, and the like.  
         [0009]     In accordance with another embodiment of the invention, a control circuit for an actuator is provided. The control circuit includes an analog central pattern generator circuit structured to generate a sine wave shaped control signal at an output and an analog multi-vibrator circuit having an input coupled to the output of the central pattern generator and an output configured to be coupled to the actuator. The analog multi-vibrator circuit is structured to generate a sine-variable rectangular wave signal in response to the control signal from the central pattern generator to drive the servo in a smooth sine movement pattern.  
         [0010]     In accordance with another embodiment of the invention, a basic motor neuron circuit is provided. This circuit includes a first transistor having a control terminal coupled to an input, a first terminal coupled to a voltage source and a second terminal; a second transistor having a control terminal coupled to the second terminal of the first transistor, a first terminal coupled to the voltage source and to an output, and a second terminal coupled to a reference voltage; and a third transistor having a control terminal coupled to the output and to the voltage source, a first terminal coupled to the voltage source, and a second terminal coupled to the reference voltage. Ideally, bipolar or integrated NPN or PNP transistors are used.  
         [0011]     In accordance with another aspect of the foregoing embodiment, this basic motor neuron circuit preferably includes a first capacitor coupled between the control terminal of the third transistor and the output, and a second capacitor coupled between the first terminal of the third transistor and the control terminal of the second transistor, the first and second capacitors configured to control timing for the circuit.  
         [0012]     In accordance with another embodiment of the invention, the basic motor neuron circuit includes a first resistor and a second resistor coupled in series between the control terminal of the second transistor and the voltage source and configured to control a pulse width of a pulse signal generated on the output.  
         [0013]     In accordance with yet another aspect of the invention, a robotic system is provided having at least one movable component coupled to a servo that generates movement of the component, the robotic machine including: a control circuit coupled to the servo for controlling actuation of the servo, the control circuit including: a first transistor having a control terminal coupled to an input, a first terminal coupled to a voltage source and a second terminal; a second transistor having a control terminal coupled to the second terminal of the first transistor, a first terminal coupled to the voltage source and to an output, and a second terminal coupled to a reference voltage; and a third transistor having a control terminal coupled to the output and to the voltage source, a first terminal coupled to the voltage source, and a second terminal coupled to the reference voltage.  
         [0014]     In accordance with yet a further embodiment of the invention, a synthetic nervous system for robotic applications having a control circuit and servo actuators using continuously variable analog voltages to mimic natural bio-neural processes is provided that includes a central pattern generator utilizing periodic, quasi-periodic, or chaotic oscillators or phase shifters, or a combination thereof, along with a basic motor neuron circuit. Ideally the system enables multiple motor neurons to coordinate their behavior to enable such things as walking, swimming, flapping, crawling, and the like. Sensors interfaced to the control circuit provide a wide range of adaptive behavior such as following light, avoiding an obstacle, and shifting a balance point. Overlapping or concurrent behavior can provide complex behaviors with minimal circuitry.  
         [0015]     As will be readily appreciated from the foregoing, the approach of the present invention is fundamentally different from prior designs. Some contemporary systems use an integrate-and-fire design to robotics locomotion control using an adaptive ring oscillator while the present invention uses simple phased, coupled continuously variable analog logic and oscillators implemented as oscillating infinite state machines that can be modulated in frequency, phase, amplitude, and DC offset. These oscillators are used as computational elements capable of maximizing processing power while minimizing circuitry.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The foregoing and other features and advantages of the present invention will be more readily appreciated as the same become better understood from the following detailed description when taken in conjunction with the accompanying drawings, wherein:  
         [0017]      FIG. 1  is a circuit diagram of a basic motor neuron circuit formed in accordance with the present invention;  
         [0018]      FIG. 2  is a circuit diagram of a master-slave central pattern generator formed in accordance with the present invention;  
         [0019]      FIG. 3  is a frequency-modulated central pattern generator formed in accordance with the present invention;  
         [0020]      FIG. 4  is a circuit diagram of a variable master-slave central pattern generator formed in accordance with the present invention;  
         [0021]      FIG. 5  is a circuit diagram of an amplitude modulator circuit for use with a central pattern generator formed in accordance with the present invention;  
         [0022]      FIG. 6  is an illustration of a DC offset modulator circuit for use with the basic motor neuron circuit and central pattern generator circuits;  
         [0023]      FIG. 7  is a diagram of a control circuit for a four-legged eight-servo light-seeking robotic walker formed in accordance with the present invention;  
         [0024]      FIG. 8  is a diagram illustrating the topology of a synthetic nervous system formed in accordance with the present invention;  
         [0025]      FIG. 9  is a schematic of a motor neuron circuit utilizing a 555 timer chip formed in accordance with the present invention;  
         [0026]      FIGS. 10A-10C  are circuit schematics for a short-term memory as used for a two-servo walker with an analog input formed in accordance with the present invention;  
         [0027]      FIG. 11  is a circuit schematic of an alternative central pattern generator utilizing a NE567 tone decoder chip in accordance with the present invention;  
         [0028]      FIG. 12  is a circuit schematic for an eight-transistor two-servo photowalker formed in accordance with the present invention;  
         [0029]      FIGS. 13A-13B  are a circuit schematic and corresponding topology diagram of a control circuit for a two-servo walking light follower formed in accordance with the present invention;  
         [0030]      FIGS. 14A through 14D  are a topology diagram and accompanying circuit schematics for a phase switch matrix control circuit and voltage-to-position converter configured for use with a four-legged eight-servo walker formed in accordance with the present invention;  
         [0031]      FIGS. 15A and 15B  are a circuit schematic and accompanying topology diagram for a learning connectionist synapse formed in accordance with the present invention;  
         [0032]      FIGS. 16A and 16B  are a circuit schematic and corresponding topology diagram for a learning connectionist neuron formed in accordance with the present invention;  
         [0033]      FIG. 17  is a topology diagram of an input synapse array formed in accordance with the present invention;  
         [0034]      FIG. 18A  is an oscilloscope waveform diagram of the outputs of the master-slave central pattern generator of  FIG. 2 ;  
         [0035]      FIG. 19  is an oscilloscope waveform diagram of the output from a modified central pattern generator for use with a four-legged eight-servo walker;  
         [0036]      FIG. 20  is an oscilloscope waveform diagram of the output of a modified central pattern generator for use with a four-legged eight-transistor walker; and  
         [0037]      FIG. 21  is an oscilloscope waveform diagram illustrating the output of a near-chaotic central pattern generator formed in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0038]      FIG. 1  is a circuit diagram of a basic motor neuron circuit  10  formed in accordance with one embodiment of the invention. This circuit is configured as a waveform generator for use with commercially available model-hobbyist type servos. The circuit  10  includes a rectangular wave multi-vibrator circuit formed of a first transistor (Q 1 )  14  and a second transistor (Q 2 )  16 . A third transistor (Q 3 )  18  is configured to operate as a voltage-controlled resistor and is coupled between an input  20  (Vin) and a control terminal or base of the first transistor  14 . A first resistor  22  (R 1 ) is coupled between the input  20  and the control terminal or base of the third transistor  18 , and a second resistor  24  (R 2 ) is coupled between the control terminal or base of the third transistor  18  and a voltage source  26 , which is preferably set at 5 volts for this application. The second resistor  24  provides a bias to the third transistor  18  so that it operates in the linear region and, functionally, as a voltage-controlled resistor.  
         [0039]     The third transistor  18  has a first terminal coupled to the voltage source  26  and a second terminal coupled to the voltage source  26  through a third resistor  28  (R 3 ) and also to a control terminal of the first transistor  14  via a fourth resistor  30  (R 4 ). The first transistor  14  has a first terminal coupled to the voltage source  26  via a fifth resistor  32  (R 5 ) and also coupled via a sixth resistor  34  (R 6 ) to an output  36  (SERVO OUT). In addition, the first terminal of the first transistor  14  is also coupled to a control terminal of the second transistor  16  via a first capacitor  38  (C 1 ). The control terminal of the second transistor  16  is also coupled to the voltage source  26  via a seventh resistor  40  (R 7 ) and to ground or a reference potential  46  through a second capacitor  43  (C 2 ). The first terminal of the second transistor  16  is coupled to the voltage source  26  via an eighth resistor  42  (R 8 ) and to the control terminal of the first transistor  14  via a third capacitor  44  (C 3 ). The second terminals of the first and second transistors  14 ,  16  are coupled to a common reference potential  46 , shown in this example with a ground symbol. A fourth capacitor  45  (C 4 ) is coupled between the base of Q 1  and ground  46 .  
         [0040]     As described above, the first and second transistors  14 ,  16  are coupled together to function as a square wave multi-vibrator. The fifth resistor  32  and the eighth resistor  42  are chosen to obtain a desired waveform at the output  36 . The first and third capacitors  38 ,  44  are the timing capacitors for the circuit  10 . The seventh resistor  40  controls the time between pulses at the output  36 , and the value of this resistor is not critical so long as it provides pulses in the range of 20 milliseconds to 50 milliseconds. The third and fourth resistors,  28 ,  30  along with the third transistor  18  control the length of the pulse. Preferably, the third and fourth resistors  28 ,  30  are chosen to give about a 2-millisecond pulse, but the fourth resistor  30  can be variable to choose whatever is appropriate for the circuit.  
         [0041]     The Vin input  20  functions as a signal summation point for the output of other circuits to be described below. Zero volts at the Vin input  20  provides roughly a 2-millisecond pulse at the output  36 , and 5 volts at the input  20  provides approximately 1-millisecond pulses. These pulses are preferably provided directly to a commercially available servo (not shown in  FIG. 1 ) that has an input coupled to the output  36  of the circuit  10 .  
         [0042]     Bipolar or integrated NPN transistors are used in this basic motor neuron circuit  10 . While operational amplifiers can be used, such as those fabricated using CMOS technology, cost and simplification is a goal and hence operational amplifiers are not preferred for this circuit.  
         [0043]     Turning next to  FIG. 2 , shown therein is a master-slave central pattern generator circuit  48  formed in accordance with the present invention to include a first section  50  and a second section  52 . The first section  50  includes a fourth transistor (Q 4 )  54  having a control terminal coupled to a voltage source  56 , which could be the same voltage source  26  used with the basic motor neuron circuit  10  when these circuits are coupled together. A ninth resistor  58  (R 9 ) is interposed between the voltage source  56  and the control terminal of the fourth transistor  54 . The fourth transistor  54  has a first terminal coupled to the voltage source  56  via a tenth resistor  60  (R 10 ) and also coupled to an output  62  (OUT 1 ) via an eleventh resistor  64  (R 11 ). The first terminal of the fourth transistor  54  is also coupled to the control terminal of a fifth transistor (Q 5 )  66  via a twelfth resistor  68  (R 12 ).  
         [0044]     The fourth transistor  54  also has its first terminal coupled to its control terminal via a fourth capacitor  70  (C 4 ), fifth capacitor  72  (C 5 ), and sixth capacitor  74  (C 6 ) series coupled together. A second terminal of the fourth transistor  54  is coupled to a ground or reference potential  76  and to a sixteenth resistor  78  (R 16 ) that is coupled between the fourth and fifth capacitors  70 ,  72  and to a seventeenth resistor  80  (R 17 ) coupled between the fifth capacitor  72  and the sixth capacitor  74 .  
         [0045]     Turning to the second section  52 , this section includes the fifth transistor  66  in which the control terminal is coupled to the voltage source  56  via a thirteenth resistor  82  (R 13 ), a first terminal is coupled to the voltage source  56  via a fourteenth resistor  84  (R 14 ), and to an output  86  (OUT 2 ) via a fifteenth resistor  88  (R 15 ). In addition, the fifth transistor  66  has its first terminal coupled to its control by series connected seventh, eighth, and ninth capacitors  90 ,  92 ,  94 . The second terminal of the fifth transistor  66  is coupled to the ground or reference potential  76 , and to an eighteenth resistor  96  (R 18 ) coupled between the seventh and eighth capacitors  90 ,  92 , and to a nineteenth resistor  98  (R 19 ) coupled between the eighth and ninth capacitors  92 ,  94 .  
         [0046]     In operation, the first and second sections  50 ,  52  are single transistor sine wave oscillators. The sixteenth through the nineteenth resistors  78 ,  80 , and  96 ,  98  and the fourth through the ninth capacitors  70 ,  72 ,  74 , and  90 ,  92 ,  94  cooperate to provide the RC timing constants. The RC time constant should be in the range of 0.5 to 3.0 seconds for the robotic applications disclosed herein. The time constant can be varied as necessary to meet the needs of a particular application. The value of the ninth, tenth, thirteenth and fourteenth resistors  58 ,  60 ,  82 ,  84  are chosen for best waveform output. Each of the first and second oscillators  50 ,  52  has its own basic motor neuron output  62 ,  86  through the eleventh resistor  64  and the fifteenth resistor  88 , respectively. The first section  50  has its output coupled OUT 1  to the input  20  of the basic motor neuron circuit  10  shown in  FIG. 1 . The second output  86  (OUT 2 ) is likewise coupled to a basic motor neuron circuit for actuating a second servo (not shown). The second section  52  is a slave that is out of phase with the first section  50 . The central pattern generator  48  does not have an input and commences generating a single sine wave at the OUT 1  output  62  of the first section  50  upon power-up.  
         [0047]     The first and section sections  50 ,  52  are lightly coupled together through the twelfth resistor  68 . In this manner, the second section  52  becomes phase locked and phase shifted with respect to the first section  50 . The first, second, and fourth periods and chaotic phase orbits of these circuits can be measured at the twelfth resistor  68  and a fifteenth resistor  88  with proper adjustment of the tenth resistor  60  and the fourteenth resistor  84 , which are used to modify the sine wave output.  
         [0048]     By coupling the output  62  of the first section  50  to the input  20  of the basic motor neuron circuit  10 , a sine variable rectangular waveform will appear at the output  36  of the basic motor neuron circuit  10 , which is used as an input to a servo or actuator (not shown in this FIGURE). This will cause a rotatable shaft in the servo to turn back and forth in a smooth sine pattern. This back-and-forth motion forms the basic action of robotic locomotion in a synthetic nervous system consisting of the basic motor neuron circuit  10  and the central pattern generator circuit  48 .  
         [0049]     Adding an additional RC pole to the central pattern generator sine wave signal will provide greater oscillator stability and modify the sine wave so that it may be more appropriate to certain locomotion schemes.  
         [0050]     Turning next to  FIG. 3 , shown therein is a frequency modulated central pattern generator circuit  100  formed in accordance with another embodiment of the present invention. This circuit  100  includes a sixth transistor  102  (Q 6 ) having its control terminal coupled to a voltage source  104  via a twentieth resistor  106  (R 20 ), and having its first terminal also coupled to the voltage source  104  via a twenty-first resistor  108  (R 21 ). The first terminal is also coupled to an output  110  (OUT 3 ) via a twenty-second resistor  112  (R 22 ) and to its control terminal by series coupled tenth, eleventh, and twelfth capacitors  114 ,  116 ,  118 . The sixth transistor also has a second terminal that is coupled to a ground or reference potential  120  and to a twenty-third resistor  122  (R 23 ) that has its other terminal coupled between the tenth and eleventh capacitors  114 ,  116 . A tenth transistor  124  (Q 10 ) has its control terminal coupled to a 5-volt voltage source, such as the voltage source  104  referenced above, via a twenty-fifth resistor  126  (R 25 ) and also coupled to a frequency input terminal  128  via a twenty-fourth resistor  130  (R 24 ). This tenth transistor  124  has a first terminal coupled between the eleventh and twelfth capacitors  116 ,  118  and a second terminal coupled to the ground or reference potential  120  via a twenty-sixth resistor  132  (R 26 ).  
         [0051]     This frequency-modulated central pattern generator circuit  100  is configured to replace one of the RC timing resistors, such as the nineteenth resistor  98  in the master-slave central pattern generator  48  or the seventeenth resistor  80  in the first section  50  thereof. For example, if the nineteenth resistor  98  were replaced with the frequency-modulated central pattern generator circuit  100 , the output  110  (OUT 3 ) of the central pattern generator circuit  100  would be coupled between the eighth and ninth capacitors  92 ,  94 . The twenty-fourth through the twenty-sixth resistors  130 ,  126 ,  132 , respectively, and the sixth transistor  102  cooperate to act as a high-impedance voltage controlled resistor. This enables modification of the central pattern generator  48  so that it can be sped up or slowed down, and it also allows for more complex waveforms. Thus, this central pattern generator circuit  100  provides for frequency modification of the central pattern generator  48  of  FIG. 2  and hence of the basic motor neuron circuit  10 . In use this circuit controls the speed of movement from walking to running.  
         [0052]     Turning next to  FIG. 4 , shown therein is a variable master-slave central pattern generator circuit  140  modified to enable phase shifting of the output signal, which allows reversing of the circuit and hence the motion of the servo connected at the output  36  (SERVO OUT) of the basic motor neuron circuit  10  shown in  FIG. 1 . In  FIG. 4 , elements in common with those shown in  FIG. 2  have the same reference number. Here, eleventh, twelfth, and thirteenth transistors  134 ,  136 ,  138  (Q 11 , Q 12 , Q 13 ) are added to the circuit  48  of  FIG. 2  to form the variable master-slave central pattern generator circuit  140 . The twelfth transistor  136  has a control terminal coupled to a phase shift input  144  via a twenty-seventh resistor  142  (R 27 ), and a first terminal coupled to the twelfth resistor  68 . A second terminal of the twelfth transistor  136  is coupled directly to the control of the fifth transistor  66 . The eleventh transistor  134  has a control terminal coupled to the phase shift input  144  via a twenty-eighth resistor  146  (R 28 ), a first terminal coupled to the 5-volt voltage source  56 , and a second terminal coupled to the control of the thirteenth transistor  138  by a twenty-ninth resistor  148  (R 29 ) and to the positive voltage reference potential  76  via a thirtieth resistor  150  (R 30 ). Finally, the thirteenth transistor  138  has its first terminal coupled to the first terminal of the fifth transistor  66  via a thirty-first resistor  152  (R 31 ) and its second terminal coupled directly to the control of the fourth transistor  54 .  
         [0053]     In this modified variable central pattern generator  140 , the eleventh transistor  134  (Q 11 ) receives a O-volt to 5-volt phase shift input signal at the phase shift input  144  to invert the phase shift signal so that only the twelfth or thirteenth transistor  136 ,  138 , (Q 12 , Q 13 ) respectively, is on at any one time. These two transistors are structured to control the flow of information, and this simple arrangement allows the twelfth transistor  136  to be phase shifted from about 90 degrees to 270 degrees in relation to the thirteenth transistor  138 , enabling simple reversing of the robotic direction.  
         [0054]     Amplitude modulation of the sine wave output signal generated by the central pattern generator  48 ,  140  is provided via an amplitude modulator circuit  154  shown in  FIG. 5 . Here, a seventh transistor (Q 7 )  156  has its control terminal coupled to an amplitude input  158  via a thirty-second resistor  160  (R 31 ) and to a voltage source, such as voltage source  56 , via a thirty-third resistor  162 . The first terminal of the seventh transistor  156  is coupled to the output  62  (OUT 1 ) of the first section  50 , and the second terminal  157  of this transistor forms the output of the amplitude modulator circuit  154 , which is received at a DC offset modulator circuit  164  in  FIG. 6 . An amplitude input control signal is received at the amplitude input  158 . The amplitude modulator circuit is used to control the amount of limb swing or rotation, such as length of stride.  
         [0055]     Turning to  FIG. 6 , the DC offset modulator circuit  164  consists of series-coupled eighth and ninth transistors  166 ,  168  (Q 8 , Q 9 ) in which the control terminal of the eighth transistor  166  is coupled to a first offset input  170  (Offset 1 ) via a thirty-fourth resistor  172  (R 34 ), a second terminal is coupled to a DC input  174  (DCin) via a thirty-fifth resistor  176  (R 34 ). The ninth transistor  168  has a control terminal coupled to a second DC offset input  178  (Offset 2 ) via a thirty-sixth resistor  180  (R 36 ).  
         [0056]     The eighth transistor  166  also has a first terminal coupled to a voltage source  56  via a thirty-seventh resistor  182  (R 37 ), and its second terminal is also coupled to a DC output  184  (DCout) via a thirty-eighth resistor  186  (R 38 ). The ninth transistor  168  has its first terminal coupled to the second terminal of the eighth transistor  166  and hence to the thirty-eighth resistor  186 . A second terminal of the ninth transistor  168  is coupled to the ground reference potential  76  via a thirty-ninth resistor  188  (R 39 ).  
         [0057]     The DC offset modulator circuit  164  is configured so that the DC input  174  is coupled to the second terminal  157  of the seventh transistor  156  in the amplitude modulator circuit  154 . The DC output  184  is then coupled to the Vin input  20  of the basic motor neuron circuit  10  of  FIG. 1 . The DC offset modulator circuit  164  is utilized for balancing and steering of the robotic machine in combination with the amplitude modulator circuit  154  of  FIG. 5 . The amplitude modulator circuit  154  provides for amplitude adjustment of the sine wave output from the sine wave oscillator of the first section  50 .  
         [0058]     The DC output  184  from the DC offset modulator  164  and the output  110  from the frequency-modulated central pattern generator circuit  100  are configured to be summed at the Vin input  20  of the basic motor neuron circuit  10  to provide full control of the servos and the resulting movement of the robotic machine. For example, DC offset to one set of servos will cause turning of the robotic walker machine.  
         [0059]      FIG. 7  is a synthetic nervous system or control circuit  190  for a four-legged eight-servo light-seeking robotic walker machine. The control circuit  190  in one embodiment utilizes sixteen oscillators and thirty-four transistors, preferably NPN transistors, arranged as a synthetic nervous system. Pairs of sine oscillators are configured as central pattern generators  48 , shown in  FIG. 2 , to control each leg of the robotic machine. More particularly, a first leg control circuit  192  includes oscillators Sine  1  and Sine  2 , which are the first and second sections  50 ,  52  of the central pattern generator  48  of  FIG. 2 . Coupled to Sine  1  is the amplitude modulator circuit  154  that in turn is coupled to the basic motor neuron circuit  10  of  FIG. 1 , as is Sine  2 , which is coupled to the output  86  from the second section  52  for the basic motor neuron circuit  10 .  
         [0060]     Similar construction is used for the second leg control circuit  194 . The third and fourth leg control circuits  196 ,  198  only utilize the central pattern generator  48  and the basic motor neuron circuit  10 .  
         [0061]     Sine oscillators  1 ,  3 ,  5 , and  7  are configured to control forwards and backwards leg swing while Sine oscillators  2 ,  4 ,  6 , and  8  are configured to control the up and down movements of the leg. Amps  1  and  2  are the amplitude modulator circuits  154  of  FIG. 5  that are controlled through a cross-connected light-dependent sensor circuit  200 . The sensor circuit  200  consists of a first light dependent resistor  202  and second light dependent resistor  204  powered by the voltage source  26 , preferably at 5 volts, and connected to ground reference potential  46  via first and second resistive elements  206 ,  208 . A first output node  210  is formed at the connection between the first resistive element  206  and the first light dependent resistor  202 , and a second output node  212  is formed at the connection between the second resistive element  208  and the second light dependent resistor  204 . The first output node  210  is coupled to the amplitude input  158  of Amp  2 , and the second output node  212  is coupled to the amplitude input  158  of Amp  1 . This controls the amount of swing in the front legs in proportion to the amount of light received at the light dependent resistors  202 ,  204 . Cross-tying the light dependent resistors  202 ,  204  enables light-seeking behavior by the robotic machine.  
         [0062]     The collector of Sine  1  is wired to the base of Sine  7 , as is the collector of Sine  1  wired to the base of Sine  2 . Sine  1  and  7  are locked about 90 degrees out of phase. Sine  7  is connected to Sine  5  and  8  in the same collector-to-base fashion. Sine  5  is connected to Sine  3  and  6 , and Sine  3  is connected to Sine  4 . Ideally, these connections are made through a resistor, preferably of a value similar to the value of resistor  68  (R 9 ) of  FIG. 2 .  
         [0063]     All of the leg pairs  192 ,  194 ,  196 ,  198  are phase locked roughly 90 degrees from each other. On an oscilloscope in the “XY” setting, this will show a roughly circular phase orbit. When connected to the basic motor neuron circuit  10  and wired to a servo, this will cause the legs to show forward locomotion.  
         [0064]     Because Sine oscillators  1 ,  7 ,  5 , and  3  are roughly 90 degrees out of phase, this will cause each leg in the robotic machine to swing forward in proper phase unison. Because Sine oscillators  2 ,  4 ,  6 , and  8  are driven by the second section  52 , which is phase shifted from the first section  50 , this will coordinate lifting of the legs at the time the legs are moving forward, thus enabling a forward walking motion. Amps  1  and  2  control the amount of leg swing through signals received from the light sensor circuit  200  to enable the robotic machine or quadropod to walk towards a light source.  
         [0065]     As will be readily appreciated from the foregoing, the “basic motor neuron” circuit described above utilizes a two-transistor multi-vibrator in combination with a third transistor having a high impedance on its base that is functional as a voltage variable resistor. This circuit outputs ideally a 1-2 millisecond pulse train that is needed to control a servo. While an existing JFET MPF102 transistor has been used as the third transistor, much better and linear results using a less-expensive 2n222 NPN transistor can be obtained with lower cost and complexity. Other circuits, such as a 555 timer chip, op amps and diodes, can be used, but the preferred embodiment described above is in keeping with the goal of a straightforward, simple robust circuit. A chip such as the PIC 12F675, however, can be used in place of two basic motor neuron circuits, which replaces 30 or more electronic components by digitizing the oscillators and outputting a proper signal.  
         [0066]     While the foregoing embodiment is still somewhat complicated, involving 34 transistors, 16 of them implemented as oscillators, 8 of which are phase-locked and some of which are phase-locked to multiple oscillators, a more simplified two-servo light-following walking robot can be built with a touch sensor that uses 555 timer chips to replace the transistors in the basic motor neuron circuit along with two phase-coupled sine oscillators. In one embodiment, two 555 timers, two transistors, two servos, and several passive sensors and components can be used to provide a substantial amount of processing power. Additional features and alternative embodiments of the present invention will now be described in conjunction with  FIGS. 8-21 . The goal here is to simplify the basic motor neuron circuit using a 555 timer design having only six external components, ideally working almost identical to the three-transistor basic motor neuron circuit described above. One 555 timer is needed per servo. The sine oscillators are identical to the ones described above.  
         [0067]     Referring to  FIG. 8 , shown therein is a synthetic nervous system topology  220  for a single motor neuron  222  coupled to an actuator  224  such as a servo.  FIG. 8  further shows amplitude and DC offset circuits  226 ,  228 , respectively, series coupled as inputs to the motor neuron  222 . An oscillator  230 , such as a pacemaker neuron, receives a frequency input from a frequency circuit  232  and other optional oscillators  234  and a phase circuit  236  to generate an output that is received at the amplitude circuit  226 . Further additional oscillators  238  can be used as input to the phase circuit  236 , all in a manner as described above with respect to the embodiments depicted in  FIGS. 1-7 .  
         [0068]     Turning next to  FIG. 9 , shown therein is an alternative embodiment of a basic motor neuron circuit  240  utilizing a 555 timer chip  242 . As shown therein, pin  1  is coupled to ground and pin  8  is coupled to a 5-volt voltage source. Resistor R 1  couples the voltage source to pin  7  and to a diode D 1 . A resistor R 2  couples pin  7  to pin  6  and to pin  2 . A capacitor C 1  couples the diode D 1  to ground. Pin  5  functions through resistor R 3  as the input to the motor neuron circuit  240 . Pin  4  is coupled to a 5-volt voltage source, while pin  3  serves as the output to the actuator.  
         [0069]     Turning next to  FIGS. 10A-10C , shown therein are a basic short-term memory circuit  244 , a short-term memory circuit  246  for a two-servo walker, and a simple analog input circuit  248  for the short-term memory circuit  246 , respectively. The basic short-term memory  244  shown in  FIG. 10A  includes three resistors and a capacitor coupled to a common node. A synapse resistor has its free terminal functioning as an analog input to the short-term memory circuit  244 . A bias resistor R bias  has its free terminal coupled to a 5-volt voltage source. A third resistor R synapse2  has its free terminal coupled to the nervous system, while the memory capacitor C m  has its free terminal coupled to ground. This is a preferred circuit for most of the applications of the present invention. The resistor R bias  prevents self-discharge. The circuit of  FIG. 10A  is utilized in controlling and influencing nervous system behavior, such as a bump switch, phase shifter, modulator, etc.  
         [0070]     In  FIG. 10B , the short-term memory circuit  246  has a switch Sw with one terminal coupled to a 5-volt voltage source and a second terminal coupled to resistor R synapse  and to a memory capacitor C memory  that has its free terminal coupled to ground. The connection between the switch Sw, capacitor C memory  and resistor R synapse  is optionally coupled to a ground through an optional resistor R optional . The free terminal of the resistor R synapse  is coupled to a phase switcher.  
         [0071]      FIG. 10C  illustrates the simple analog input  248  to the short-term memory circuit  246  and includes a first bias resistor R bias , having one terminal coupled to a 5-volt voltage source and a second terminal coupled to a switch that has its second terminal coupled to a second terminal of a second bias resistor R bias2 , whose free terminal is coupled to ground. The connection between the two bias resistors R bias1  and R bias2  serves as the output to the short-term memory  246 . Thus, the analog input circuit  248  provides a convenient way to charge the capacitor C memory , making the circuit self-adjusting, such as when a leg over-impacts a surface. This is used to adjust the DC offset modulation. Thus, the short-term memory circuit  246  can be considered as a combination of the basic short-term memory circuit  244  and the analog input circuit  248  for use in controlling phase switches to control functioning of the nervous system.  
         [0072]     Turning next to  FIG. 11 , shown therein is an alternative embodiment of a central pattern generator circuit  250  that uses a quadrature oscillator with outputs going through a first order low-pass filter. More particularly, the central pattern generator circuit  250  utilizes an NE567 tone decoder/phase-locked loop chip  252  having pins  1  and  2  open, pin  3  coupled to a phase inverter, and pin  4  coupled to a 5-volt voltage source. Pin  8  is coupled to a 5-volt voltage source through a first resistor R 1  and to a phase  1  output through resistor R 2 . Pin  7  is coupled to ground and to the phase  1  OUT through capacitor C 2 . The capacitor C 1  coupled pin  7  to pin  6 . Pin  6  is also coupled to pin  5  through resistor R 4  and to a second output phase  2  OUT via resistor R 3 . The phase OUT is also coupled to ground through a capacitor C 3 . A first transistor Q 1  and second transistor Q 2  are coupled in reverse parallel relationship with the gate of Q 1  coupled to a 5-volt voltage source through resistor R 5  and to a frequency modulated input through resistor R 7 . A first terminal of resistor Q 1  is coupled to the sixth pin of the chip  252  and a second terminal of Q 1  is coupled to the fifth pin of the chip  252 . The second terminal of Q 1  is also coupled to the first terminal of Q 2  which has its second terminal coupled to pin  6 . The control terminal of transistor Q 2  is coupled to the 5-volt voltage source through resistor R 6  and coupled to the frequency modulated input through resistor R 8 .  
         [0073]     As can be seen therein, resistors R 1 , R 5 , and R 6  function as bias resistors, while resistors R 2  and R 3  are first order low-pass resistors. Resistor R 4  is a timing resistor cooperating with capacitor C 1 , which is a timing capacitor. Capacitors C 2  and C 3  are first order low-pass capacitors, while transistors Q 1  and Q 2  function as a voltage variable resistor. Phase  1  OUT and phase  2  OUT are outputs to basic motor neuron circuits, while phase invert is a control signal to swap phases at appropriate voltages. The output of this central pattern generator is close to a sine wave with a built-in phase inverter to enable change in direction of the actuator or robot. Ideally, the phase  1  OUT and phase  2  OUT are 90 degrees out of phase to provide locomotion through two actuators.  
         [0074]     It is to be understood that any appropriate analog oscillator can be used besides transistors and the 567 tone decoder disclosed herein. The advantage of transistors or operational amplifier oscillators is that they can be weakly phase-coupled to generate more complex waveforms. For high locomotion efficiency, phase-coupled oscillators should meet the Liapunov criterion for stability.  
         [0075]      FIG. 12  is an electrical schematic for an eight-transistor two-servo photowalker. This schematic shows the control circuitry  254  having a high impedance to facilitate analog sensors, photocells, tough sensors, heat sensors, and the like.  FIG. 12  shows the use of two basic motor neuron circuits  256  and  258  coupled to corresponding central pattern generators  260 ,  262 , respectively, that are lightly coupled together in a master-slave relationship. These circuits correspond to the basic motor neuron circuit and central pattern generator described above with respect to  FIGS. 1 and 2 .  
         [0076]     An additional element is the use of photocells  264 ,  266 , shown as resistor R photocell1  and resistor R photocell2  coupled in series between a 5-volt voltage source and ground. The common node between the two photocells  264 ,  266  is coupled to the input of the basic motor neuron circuit  256  via a resistor R synapse .  
         [0077]     The resistor R synapse  controls how much the photocells are enabled to influence the DC offset of the output from the central pattern generator  260 . In the context of a robot, this controls which side the front leg swings on. Thus, a light-following or light-avoiding behavior can be accomplished. It is recommended that R synapse  have an initial value of 47 k ohm for this application or embodiment. R 3 &#39;s value will have a substantial influence on how far the servo will cause the robotic limb to move. A potentiometer is recommended to initially obtain the desired results, after which a fixed resistance can be substituted. It is also to be understood that 555 timer circuits described above can be substituted for the basic motor neuron circuits  256 ,  258  illustrated herein.  
         [0078]     Turning next to  FIGS. 13A and 13B , shown therein are a control circuit  268  and circuit topology  270 , respectively, for a two-servo walking light-follower robot. This control circuit  268  is substantially similar to the control circuit  254  shown in  FIG. 12 , except it is using 555 chips in the basic motor neuron circuits  270 ,  272 . This provides a lower impedance and enables the use of commercially available 555 chips. The two illustrated photocells create a DC offset modulator to the input of the first basic motor neuron circuit  270 , which can function as the front servo. The resistor R synapse  determines the coupling&#39;s strength between the photocells R photocell1 , R photocell2 . It is recommended that a 10 k resistor be used initially for resistor R synapse  and then adjust as needed. Resistor R 3  determines the amount of coupling between the two sine oscillator circuits  274 ,  276 . Resistor R 2  on the sine oscillator circuits  274 ,  276  can be adjusted to obtain a proper waveform.  
         [0079]     Referring next to  FIG. 14A , shown therein is a phase switch matrix  280  for a four-legged quadropod. The circuit topology illustrated in  FIG. 14A  is similar to that used in the four-legged quadropod topology illustrated in  FIG. 7 , except instead of four separate sine oscillators, only one sine oscillator is used in combination with phase shifters fed through the phase switch matrix  280  to tap into different phases. Thus, all phases will be available. The sine oscillator  282  provides a sine wave output to three separate phase shifters  284 ,  286 ,  288  that each offset the sine oscillator output signal by 90 degrees and feed their outputs through respective phase switch matrix circuits  290 ,  292 ,  294 ,  296  that are also cross-coupled together.  FIG. 14C  shows in more detail the circuit schematics for one embodiment of a quad tightly-coupled central pattern generator  295  for this particular embodiment.  FIG. 14B  illustrates one embodiment of the phase switch matrix circuits  290 ,  292 ,  294 ,  296  utilizing four  4066  quad analog switches.  
         [0080]     The outputs of the phase switch matrix circuits  290 ,  292 ,  294 ,  296  are fed to respective nervous system components, such as respective basic motor neuron circuits as described above and associated voltage-to-position converters, such as the voltage-to-position circuit  297  illustrated in  FIG. 14D . The voltage-to-position converter circuit  297  is an exemplary circuit, and it is to be understood that various alternatives to this circuit that are application-dependent can be used. This circuit has a tri-state input wherein a low voltage will actuate the motor in a first direction of rotation, a higher mid-level voltage is the deadband, and a further higher voltage makes the motor rotate in an opposite second direction. The dead band range is adjustable depending on the resistance of the bias resistors. The resistor Rmotor is a potentiometer coupled to the motor shaft and provides the feedback for the circuit. This circuit can replace the basic motor neuron circuit and the circuit found in the radio controlled aircraft-type servos such that any DC gearhead motor can be used. The DC gearhead motor may function as a rotational or linear voltage to position converter depending on how it&#39;s set up. Furthermore, the DC gearhead motor may be replaced with any actuator that is bi-directional (e.g. pistons)  
         [0081]      FIGS. 15A and 15B  illustrate a learning connectionist synapse circuit  310  and related circuit topology  312 , respectively. The circuit  310  includes a 555 timer chip having the first pin coupled to ground and also coupled to the second pin via a first capacitor C 1 . The second pin is also coupled to the sixth pin directly and to the seventh pin through resistor R 2  and to the eighth pin through resistor R 3 . The eighth pin is coupled to a 5-volt voltage source. The fifth pin is coupled to a learning rate node through resistor R 4 . The fourth pin is coupled to a learning enable node directly. Pin  3  couples the 555 timer chip to a DS1804 EEPROM chip at pin  1  thereof by resistor R 5 . This is the clock input for the DS1804 chip. Pin  2  of this chip is coupled to a 1.5-volt threshold excite/inhibit signal source. Pin  3  is not connected, while pin  4  is coupled to ground. Pin  5  functions as a signal input and pin  6  is the signal output. Pin  8  is coupled to the 5-volt voltage source through resistor R 6 . Pin  7  is coupled to the 5-volt voltage source through resistor R 7  and to ground through capacitor C 2 . It is also coupled to ground through resistor R 8  and switch Sw 1 .  
         [0082]     The learning connectionist synapse  310  functions as a variable resistor, i.e., a rheostat and not a potentiometer. An array of the synapses is illustrated in  FIG. 17 .  
         [0083]     Turning to  FIG. 16B , shown therein is a learning connectionist neuron circuit  314  and related topology  316 , respectively. The circuit  314 , which is very similar to the synapse circuit  310  described in conjunction with  FIGS. 15A and 15B , has pin  3  coupled to a 5-volt voltage source and pin  6  coupled to ground. Pin  5  is the output to the nervous system. As shown in the topology of  FIG. 16B , the connectionist neuron receives input from the excite/inhibit input that in turn receives input from a sensor, such as an analog sensor. The connectionist neuron is controlled by a neuron enable signal to thus function as a potentiometer and not a rheostat. This circuit provides non-volatile changes to behavior. The 555 chip provides voltage-controlled pulses. The higher the frequency of the learning rate input, the higher the learning rate. However, too high of a frequency throws the system into oscillations. For example, it will cause a robot to overshoot and overcorrect repeatedly.  
         [0084]     The synapse circuit  310  and neuron circuit  314  provide non-volatile long-term memory. The synapse can be input to the excite/inhibit of the neuron. It modifies impedance of the sensor/analog input, influencing the weight of the sensor input. Multiple layers of synapse can be provided for non-linearity in the control system and greater flexibility. The neuron circuit  314  generates an output voltage and acts as a potentiometer instead of a rheostat.  
         [0085]     With respect to waveforms,  FIG. 18  illustrates a waveform output from the central pattern generator circuit  48  of  FIG. 2  using OUT 1  and OUT 2   62 ,  86 , respectively, as the X and Y inputs. This is a period  1  illustration, which is useful for general-purpose robotics, such as swimming.  
         [0086]      FIG. 19  shows a variation of the period  1  signal to create longer contract with a surface. For example, this variation of the period  1  waveform would be useful with the four-legged, eight-servo quadropod (loads, racing, etc.).  
         [0087]      FIG. 20  is an oscilloscope waveform display of period  4  showing variability in the output over time. While it is fairly stable, it would be useful for providing variation in stride on soft surfaces, such as sand, to prevent the robot from becoming stuck in the sand.  
         [0088]      FIG. 21  is an oscilloscope waveform display of a chaotic generator having some stability for providing more life-like, dynamic use.  
         [0089]     While preferred embodiments of the invention have been illustrated and described, it is to be understood that various changes can be made therein without departing from the scope of the invention. For example, the basic motor neuron circuit can use the 555 chip, as described above, or this chip can be replaced with a microcontroller chip that generates the proper signal. While such a chip provides less space, it does increase cost.  
         [0090]     While the present invention has been illustrated and described in conjunction with servos, such as off-the-shelf servos used in radio-controlled vehicles, it is to be understood that the present invention is applicable with any voltage-to-position converter. DC gearhead motors can be changed out for pneumatics and hydraulics, so long as there is analog feedback, such as a potentiometer, in order to know the position of the movable part.  
         [0091]     Also, a master oscillator having an op amp phase shifter may be more appropriate in some situations. In addition, although bipolartransistors have been illustrated and NPN and other integrated transistors have been described, it is to be understood that bipolar or integrated transistors may be used exclusively or in any combination thereof. Hence, the invention is to be limited only by the scope of the claims that follow and the equivalents thereof.  
         [0092]     All of the above U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety.