Abstract:
A table tennis practice system comprised of a robot and an enclosure or recycle net which catches balls returned by a player. The robot propels balls fed to it at a set rate so that a player on the other end of the table can receive practice similar to that between humans. The robot and recycle net are constructed so that the robot may be placed anywhere between the sides of one end of the table while simultaneously retrieving and recycling balls returned by a player. This lateral mobility of the robot permits serves from the corners of the table or any point between. Its recycle system does not rely on air movement for ball transportation, hence there is improved reliability. The timing system eliminates jamming when it can be caused by balls falling into the holes of perforated platters or notched wheels of timing devices at an in appropriate time.

Description:
BACKGROUND 
     This invention is related to machines used by humans to simulate practice with another human partner in the field of sports. In this case, the sport is table tennis. 
     Prior robots have been invented for sports such as tennis, table tennis, baseball and soccer. However, recycle systems have only been known to have been attempted for table tennis. At least one ball collecting system was invented for tennis (see U.S. Pat. No. 4,116,436, Bjorhn, 1978) but since the balls are not returned to a robot after collection, it is not considered to be a recycle system. U.S. Pat. No. 4,077,386 by Berliner in 1978 and some other robots employ a recycle system. 
     The convenience of a recycle system is desirable when practicing with a robot. However, at the present state of the art, recycle systems are lacking in their ability to permit the head of the robot to be positioned so that it can serve from various horizontal angles. Past recycle systems required the robot to be set in a fixed position relative to the table. This position was usually halfway between the table sides. If a recycle system returns balls to the robot via a flexible hose as in U.S. Pat. No. 4,765,618, the robot may be positioned at any suitable point between the table sides. This permits serves from various horizontal angles. Another way to do this is to omit a recycle system and feed the robot from a hopper. In the case of the hopper, it is part of the robot and therefore goes where the robot goes. 
     Although the hose system mentioned above works, it has inherent problems. The hopper also works, but there is no recycling. 
     Another problem on some earlier robots was jamming. The method of supplying balls to the head at a set rate was often achieved by rotating a notched wheel or perforated platter to convert from a multiplicity of balls to a single ball. The conversion allows successive single balls to be fed into the head. These methods often caused jamming because there is no guarantee that balls will fall into notches or perforations at the right time and place. The result is that balls sometimes get caught between fixed and moving surfaces of the ball container, thereby causing a jam. 
     Now, let us return to the problems encountered when a flexible hose is employed as a ball transportation path. In U.S. Pat. Nos. 4,559,918 and 4,765,618, the point-of-entry of balls returned to the system is a fixed trough or pan. The flexible hose permits variable lateral positioning of the robot&#39;s head and a minimum hose length is required to cover positions over the entire width of the table. 
     The energy required to return balls to the head in the foregoing robots is supplied by an electric fan, which causes the balls to travel up the hose or tube under the force of air pressure or vacuum. The length of hose or tube and the airflow speed determine the recycle time of the system. This time is the time required to retrieve a returned ball and send it to the head. If this time is relatively long, the system is unable to keep up with the rate at which balls need to be served. This limitation can only be overcome by employing a more powerful energy source, which means a larger fan and more powerful motor. In practice, a more powerful source tends to be impractical because far more noise is generated and electrical energy requirement is highly increased. 
     Yet another problem with air feed systems, is that when the travel of balls up the hose or tube is not uniform, a situation sometimes arises where the balls pile up and inhibit further travel. This inhibition is due to the inability of the air supply to overcome the weight of a few balls at pile up. The result is that recycling ceases. 
     This invention permits the head of the robot to be placed at any position between the sides of the table without employing an air recycle system. Also, it eliminates jamming of the balls in the feed system. The mobility of the head allows the operator to receive serves from any angle and eliminates the need for a separate ball container. 
     SUMMARY 
     The table tennis robot can be clamped to one end of the table at any available position between the sides of the table. A disk at the lower extremity of the robot forces the elastic bottom of the recycle net downward to form a conical trough at whatever position is chosen along the length of the net. Balls entering the recycle net enclosure are caught and roll down the incline of the trough, stopping on the disk. The balls are jostled about the disk by a rotating square platter and one by one they are lifted by an arm which is attracted by magnets affixed to a rotating wheel. This wheel clutches a lifted ball and carries it into a channel where it stops. When the wheel carries another ball it pushes the first ball further up the channel. The cycle continues and eventually the channel is filled with balls to the point where they arrive at the head of the robot. The head of the robot propels the balls one at a time onto the playing area so that a player can obtain practice. The rate at which the balls are propelled is dependent on the rotational speed of the wheel with magnets. 
     Provision is made for tilting the head of the robot to permit serves at different vertical angles. Also, the head of the robot may be oscillated in an arc of the horizontal plane and the height of the head maybe adjusted as desired. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of the robot. 
     FIG. 2 is a cut-away perspective view of the collection net and the robot as in FIG. 1. A small cut-away of the table is shown in the clamp of the robot. 
     FIG. 3 is a cut-away perspective view of the collection net and the table. It establishes the relationship between the table, collection net and robot, when viewed in conjunction with FIG.  2 . 
     FIG. 4 is a side view of the lower or ball retrieval section of the robot. 
     FIG. 5 is the opposite side view of FIG.  4 . 
     FIG. 6 is a front facing end view of the ball retrieval section of the robot. 
     FIG. 7 is a side view of the upper section of the robot. It includes the head and parts of the ball transportation path. 
     FIG. 8 is a plan of the section shown in FIG.  7 . 
     FIG. 9 is an opposite side view of FIG.  7 . 
     FIG. 10 is a schematic of the electrical power supply and remote control, which powers the robot. 
    
    
     DESCRIPTION 
     In FIG. 1, screw clamp  1  is connected via cylindrical bar  2  to rectangular bar  3 . Ninety-degree plate  4 , which is connected to bar  3 , suspends the lower section of the robot. The components on plate  5  comprise the lower portion of the robot and will be called the retrieval system throughout this description. 
     The components of the retrieval system are shown in FIGS.  4 , 5 , 6 . Electric motor  6  is mounted on plate  7 (FIG.  5 , 6 ). Plate  7  positions motor  6  so that its shaft engages wheel  8  at its periphery. The shaft  9  of wheel  8  goes through a bushing in plate  5  and protrudes on the other side of the plate. The protrusion of the shaft engages rubber-rimmed wheel  10  at its periphery. Wheel  10  is mounted on shaft  11 , which is affixed to plate  5 . Ninety-degree angled plate  12  is connected to plate  5 . A screw,  13 , going through a hole in  12  also goes through the following components; spacer  15 , ball bearing  16 , spacer  17 , and disk  18 . When the nut  19  is threaded onto screw  13 , the preceding four components are held firmly onto plate  12 . Plate  14  is free to rotate on bearing  16 , since spacers  15 ,  17  isolate the outer race of bearing  16  from the fixed surfaces of plate  12  and disk  18 . Bearing  16  is press-fitted into plate  14  and therefore permits its rotation. In FIGS. 5,  6 , it is seen that wheel  8  also engages plate  14 . This engagement is such that contact from wheel  8  is in an area of plate  14  where a complete circle centered about the center of plate  14  can be rotated by wheel  8 . Disk  18  cannot rotate, because the force of nut  19  presses it onto spacer  17 , the inner race of bearing  16 , spacer  15  and plate  12 . 
     In FIGS. 4,  6 , a cylindrical post  21  is attached at one end to plate  5 . The other end provides a pivot for lever  22 . An iron rod  23  is rigidly inserted into lever  22 . Two cylindrical magnets  20  are affixed to wheel  10  and oriented so that a pole of each, faces out from the center of wheel  10 , and is close to, but within the periphery of wheel  10 . 
     A three-sided channel  24  is connected by screws  25  to plate  5 (FIG.  5 ). Also, in FIGS. 1,  4  another screw  26  holds channel  24  onto a cylindrical post  27 . The length of the post is the width of the channel, and its other end is attached to plate  5  by screw  28 . A curved plate  29 , which has a ninety-degree bent section for mounting, is connected to plate  5  by screws  25 . 
     A cylindrical post  30  is affixed at one end into rectangular bar  3  so that its length runs parallel to channel  24 . A collar  31  fits over rod  30  and is able to slide along the rod. Set-screw  32  locks the collar onto rod  30  at any height desired. 
     Plate  33  supports the upper section of the robot by way of its connection to the bottom end of collar  31 . The views of FIG. 7,  8  omit the post and collar  30 ,  31  in order to provide a clearer view of the components on plate  33 . If FIG. 7 is compared to FIG. 1 it can be seen that side view FIG. 7 is the side nearest collar  31 . 
     On plate  33 , a ninety-degree angled plate  34  is connected to one end of plate  33 (FIGS. 7,  9 ). To this is affixed two posts  35 (one visible). Coil springs  36  are attached to each post  35  and their other ends are connected to post  27  FIG.  1 . Also mounted on plate  34  is a rectangular section of square tubing  37 . Section  37  is oriented so that one open end faces the trough of channel  24 . A curved metal plate  38 , which is attached to section  37 , protrudes into channel  24 . The other open end of section  37  faces a similar open end in another rectangular section of square tubing  39 . Section  39  can be described as a rectangular box, which has two open ends, and the vertical sides of the box are extended away from the box as shown in FIGS. 1,  7 ,  8 . Section  39  is attached to plate  40 . Plate  40  is attached to a ball bearing and its holder  41  whose shaft is affixed vertically into plate  33 . A cylindrical post  42  is connected to one end of plate  40  and its other end fits into a bearing  43  which is pressed into connecting rod  44 . The other end of  44  is connected to an eccentric  45 . Eccentric  45  is fitted to the output shaft of gearmotor  46 , which is connected to plate  47 (FIG.  9 ). Plate  47  is mounted onto posts  48 (FIGS  8 ,  9 ) which are connected to plate  33 . 
     The extended vertical sides of section  39  support a cylinder  49  which is pivoted about its diameter on shafts  50 ,  51  which go from the cylinder through holes in the extended sides (FIG.  1 , 7 ). The shaft  51 , is not visible on the drawing, however, its placement and operation are similar to shaft  50  except that shaft  51  is longer than shaft  50 , and the length that protrudes outwardly from its supporting arm, is threaded. Knob  52  is threaded onto shaft  51 , FIG.  8 . If knob  52  is tightened on to the supporting arm of shaft  51 , cylinder  49  is pulled tight against the arm. If it is adequately tight, cylinder  49  is fixed. Cylinder  49  can rotate about its pivots, if it is not held tightly by knob  52 . 
     In FIG. 7, a flanged cylinder  53  is shouldered (shoulder not visible) on one end so that it fits into cylinder  49 . Screws  54  and nuts  55  connect posts  56  to the flanged end of cylinder  53 . In FIGS. 7,  8  the screws are exposed for clarity. The nuts in FIGS. 7,  8  are partially into cylinder  53 . Plate  57  is connected to posts  56  as shown in FIG.  8 (one shown). Electric motors  58 ,  59  are mounted onto plate  57 . The motors have wheels  60 ,  61  fitted to their shafts. These motors are arranged so that at the closest proximity of the peripheries of the wheels they carry, a table tennis ball, introduced between them, is slightly compressed. The arrangement of the gap between both wheels is such that a ball traveling from left to right through cylinder  53  will go into the gap. A ninety-degree angled plate  62  confines the ball so that it can go only into the gap between wheels  60 ,  61 . In FIG. 7,  8  hinge  63  is connected atop section  37 . It carries a flap  64  whose unconnected end falls and orients the length of the flap in a vertical plane. 
     In FIG. 2, the recycle net and frame  65  are shown. The net is made of cloth. The robot in FIG. 1 is seen with a small cut-away of the end of the table top within the clamp  1 . The purpose of this figure is to show that the horizontal or bottom section  66  of the recycle net is depressed when the robot is clamped to the table. When this happens, disk  18  forces section  66  into a partially conical depression. The table is cut-away to give a clear view of the bottom of the recycle net. Section  66  is made from elastic material. 
     FIG. 8 shows the position of the recycle net relative to the table  67  and by association, the robot to the recycle net. 
     The robot is powered by an electrical power supply and remote control unit. The circuit is shown in FIG.  10 . Commercial power in the order of 100 volts enters at  70  of FIG.  10 . When switch  72  is closed, alternating current flows through fuse  71  and the left winding of transformer  73 . The right side secondary of transformer  73  has approximately 12 volts induced across its winding. This alternating voltage will cause an alternating current (AC) to flow, and bridge rectifier  74  converts the AC to direct current (DC). The robot&#39;s motors require DC at a maximum of 12 volts. Capacitor  89  improves the quality of DC by reducing ripple. The positive output of rectifier  74  supplies voltage to switch  75 ,  79 , voltage regulators (VR)  83 ,  84 . The four motors employed are  6 ,  46 ,  59 ,  58 . They are powered and controlled by VR  76 ,  80 ,  83 ,  84  respectively. When power switch  72  is closed, power is available to the entire circuit. If switch  75  is subsequently closed,  12  volts is supplied to VR  76 . Fixed resistor (R)  78  and motor  6  are both directly connected to the output of VR  76 . The other end of motor  6  is connected to the minus or (−ve) of the power supply. Resistor  78  and variable resistor  77  comprise a voltage divider which determines the output voltage of VR  76  and hence the rotational speed of motor  6 . The circuit of motor  46  operates in an identical manner to that of motor  6 . The corresponding components are switches  75 ,  79 , resistors (R)  78 ,  84 , and variable resistors (RV)  77 ,  81 . 
     The circuit of motor  59  receives power whenever the unit is powered up. The direction in which motor  59  rotates is determined by switch  85 , which is on the output of VR  83 . Switch  85  is a double pole, double throw type. The positive (+ve) voltage from VR  83  is supplied to a pole of switch  85 . The −ve terminal of the power supply is connected to the other pole on the same side or throw of switch  85 . The terminals of motor  59  are each connected to a separate common pole of switch  85 . The pair of poles for the other throw of switch  85 , are cross-connected to the +ve and −ve poles so that when a second throw of switch  85  is made, the terminals of motor  59  are supplied the opposite polarity of the first throw. R  86  and RV  87  in the circuit of motor  46 , have the same function as R  75 , RV  77  in the circuit of motor  6 . 
     The circuit of motor  58  functions identically to those of motors  6 ,  46  with the exception that its VR  84  is directly connected to the +ve of the power supply. There is no individual switch. Fixed resistor R  88  and variable resistor RV  90  function identically to R  75  RV  77 . 
     Description of Operation 
     The robot may be clamped onto the end of the table by adjusting the screw on clamp  1  after the robot has been placed in the desired position on the table. Disk  18  presses down on the bottom elastic section  66  of the recycle net. A partial cone is formed in the bottom. 
     The robot can be positioned almost anywhere on the table-end and the conical shape will be realized. 
     When balls are thrown into the enclosure of the recycle net, they roll down the incline of the cone and stop on disk  18 . When motor  6  is operated, wheel  8  is rotated and this causes square plate  14  to rotate clockwise (FIGS.  5 , 6 ). This action causes the corners of plate  14  to jostle the balls around. Eventually, a ball  68  (FIG. 4) stops between wheel  10 , curved plate  29  and plate  5 . In this stopped position, the ball is resting on top of rod  23 . Wheel  10  is driven to rotate by shaft  9  so it rotates clockwise (FIG.  1 , 4 ). Soon, one of the magnets  20  approaches iron rod  23  and the magnet attracts it. The rod is carried upward, and carries the stopped ball up along the curved plate  29  and into the gap between wheel  10  and mid-section of channel  24 . The ball is therefore clutched between wheel  10  and the mid-section of channel  24 . The clutching action is brief since only a small section of the channel faces wheel  10 . During the clutching action, the ball is carried further up the channel. When the ball is no longer clutched, it remains in the channel and is prevented from falling because wheel  10  is still rotating. 
     While rod  23  was carrying the ball upwards, it also prevented jostled balls from entering the space formerly occupied by the ball. Rod  23  is stopped on post  27  so that the magnet releases it and it falls back to its rest stop on disk  18 . At this point, another jostled ball can go into the space formerly occupied by the first ball. The other magnet on wheel  10  comes around, lifts rod  23  and the second ball up into the wheel-and-channel gap. The second ball pushes the first further up the channel. The cycle of lifting balls continues as long as motor  6  operates. Eventually, the channel is filled with balls up to plate  38 . The balls are pushed along curved plate  38  at the top of the channel (FIG.  1 , 7 ) and enter square tube section  37 . There, flap  64  is lifted about the hinge  63  and the balls go across the gap between section  37 ,  39  into square section  39  then through cylinders  49 ,  53  and out to the gap between propulsion wheels  60 ,  61 . If wheel  60  is rotating counterclockwise, the first ball will be propelled from the robot with some spin and at a speed, which is proportional to the wheel&#39;s rotational speed. If wheel  61  rotates clockwise, the ball would also be propelled with the same results except that the ball would spin in the opposite direction. If both wheels rotate simultaneously so that  60  rotates counterclockwise and  61  rotates clockwise, and their speeds are equal, then the ball would be propelled without spin. Various combinations of the speed of wheel  60 ,  61  can achieve various spins. This includes rotating both wheels in the same direction. However, in the latter case, a differential of wheel speeds must exist. 
     In FIGS.  7 , 8 , it can be seen that if gearmotor  46  is operated, the eccentric  45  on its output shaft will transfer motion through the connecting rod to drop-arm  42 , thereby causing oscillation of plate  40  about bearing  41 . The result is that section  39  and the rest of components connected to its right will oscillate over an arc in the horizontal plane, thereby permitting angled serves. Balls are able to go across the gap from section  37  to section  39 , because the opening on section  39  which faces  37 , has minimal movement during oscillation. This is so because it is at a small distance away from the pivot  41 . Set screw  32 , post  30  and collar  31  permit adjustment of the height from which balls are propelled. Knob  52  (FIG. 8) permits tilt, thereby allowing propulsion of the ball through various vertical angles. 
     The hinge  63  and flap  64  comprise a relief valve. When the robot-head is adjusted to a lower height, less space is available in the channel, and so balls escape by forcing flap  64  upwards and out of sections  37 , 39 .