Abstract:
An exercise machine has automatic and programmable resistance selection apparatus with vertically aligned weights that are selectable by rotably engaging a lift pin to select each weight stack. The exercise machine further includes a control panel from which the number of weights to be lifted can be ordered by the user. Alternatively the number of weights being lifted may be programmed from a remote location.

Description:
[0001]    This application claims the benefit of U.S. Provisional patent application Ser. No. 60/213839 filed Jun. 23, 2000, which is incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to an exercise machine that can be adjusted easily for various resistance levels. More particularly, this invention relates to remotely adjustable or programmable resistance exercise machines.  
           [0004]    2. Description of Related Art  
           [0005]    Physical exercise for strength training or bodybuilding consists of a sequence of movements that begins at a rest position, provides a stress on a particular muscle or group of muscles for a period of time and then ends at the rest position.  
           [0006]    There are at least three types of machine-based exercises:  
           [0007]    1. Isokinetic—The machine is programmed to pace the cycle at a constant speed. If the user moves faster, he or she encounters a higher resistance. If the user moves slower, he or she encounters less resistance. This type of exercise is currently not favored for muscle build-up.  
           [0008]    2. Isometric—The user exerts a force with no movement (e.g. against a wall). This type of exercise is used in physical therapy where damage to the ligaments prohibits large movements. It is not applicable for general muscle building.  
           [0009]    3. Isocentric—The machine provides a constant force or torque as a resistance. This is currently the most desirable type of exercise for muscle building.  
           [0010]    Various methods of generating constant resistance for machines that can be used to perform isocentric exercises have been suggested in the art. These include machines relying on magnetic clutch resistance, direct DC motor resistance, hydraulic and pneumatic resistance (both passive resistance and work against active pressure sources), springs, weights and combinations of these technologies.  
           [0011]    Market research indicates a strong preference by users for machines that use weights as the active resistance element. The smooth and even operation of well-designed weight machines has been the key to their acceptance. Some advanced technology machines based on direct motor drive, as illustrated by U.S. Pat. No. 5,020,794, Englehardt et al., have gained limited acceptance in upscale professional gyms. However, the inherent cost of the components, the electronics and the power requirements to operate such machines have made them uneconomical for the home market.  
           [0012]    While selectable weight stacks, and even motor-driven selectable weight stacks, have been disclosed in the prior art, they suffer from several disadvantages.  
           [0013]    U.S. Pat. No. 5,876,313 (Krull) shows a radial weight selector incorporated into exercise machines. The Krull patent shows selector pins engaged such that all the weights that are selected are engaged simultaneously. Although Krull further demonstrates that a single weight stack is not adequate to cover the range of resistance that is required for an exercise machine and illustrates a dual weight stack having weights that are placed side by side to achieve a full weight range, Krull utilizes a bulky and expensive design that requires four guide rods. The rods must be manufactured of a strong metal, be precisely machined to be straight, then mounted precisely. Further, each weight must have low-friction linear bearings to allow the weights to move smoothly along the axis that is dictated by the guide rods. The two stacks placed side-by side require a large footprint. The combined stacks are not likely to fit in the footprint of most common weight exercise machines, thus requiring a complete redesign of such machines.  
           [0014]    Krull teaches a selector assembly that is rotated either by a motor, which is mounted on the selector, or by dropping the assembly onto a set of gears that are rotated mechanically or by a motor. The first solution requires that the motors be lifted along with the weights. This approach is undesirable because of the extra weight of the motors, motor stress, and the difficulties associated with providing power to a reciprocating motor. The second solution, where the selector engages a set of gears in the base, requires a precise alignment of the gears and will likely cause the selector to be misaligned after the completion of a number of cycles during which the selector may be rotated and can ultimately cause a critical failure.  
           [0015]    Other Krull patents disclose exercise machines that address weight selection mechanisms. These also suffer from various disadvantages. These patents include U.S. Pat. Nos. 5,935,048, 5,944,642 and 6,033,350.  
           [0016]    The patents to Lowe (U.S. Pat. No. 6,117,049), Scaramucci (U.S. Pat. No. 6,015,367) and La Lanne (U.S. Pat. No. 3,647,209), as well as U.S.S.R. Patent 1,389,789, are further examples of selectable weight stacks. The La Lanne patent discloses a radial weight selection mechanism; the Scaramucci patent discloses a weight mechanism selected by hooks; the Lowe patent discloses a motor-driven mechanism driving a threaded shaft to select the weights; and the U.S.S.R. patent discloses spring-load radial plungers for the weight selection.  
           [0017]    These patents suffer from the disadvantages of providing relatively complex mechanisms. Moreover, the Lowe patent, which discloses a motor-driven selection mechanism, suffers from the further disadvantage of requiring the motor to be mounted on the weights and for the motor to move, as the weights are lifted.  
           [0018]    As will be explained hereinafter, the present invention combines the use of weights with the ability to remotely select the weights, for example by a motor-driven selector mechanism, while at the same time avoiding the disadvantages of the prior art. The technology also lends itself to mechanized selection of the weight using flexible cables and mechanical dials. An application for such a mechanism is found in commonly available exercise machines where direct access to the weight stack is limited due to the elaborate structure of these machines. Because the resistance is generated by the pull of gravity on the weights, the design is energy efficient and is only marginally more expensive than a conventional, pin-selected weight stack machine.  
         SUMMARY OF THE INVENTION  
         [0019]    An object of this invention is to provide an exercise machine having remote and programmable resistance selection.  
           [0020]    A further object of this invention is to provide an exercise machine having a motor-driven selector for selecting the weights in which the motor does not move with the weights as the weights are raised or lowered.  
           [0021]    Another object of this invention is to provide an exercise machine with nestable, multiple weight stacks that are selectable by engaging a single lift pin pair to select each weight of a weight stack.  
           [0022]    The exercise machine of this invention uses weights as a resistance against which the various muscles are exercised. Although not limited to a particular market, the goal is to provide a machine that can be economically offered to the home market while still providing the advantages of more expensive exercise machines. One advantage is to provide an exercise machine with programmable resistance capabilities. In an exercise machine with programmable resistance capabilities, the user can select the desired resistance through a panel from the seat. A complete workout can be pre-programmed and the user follows the machine in “Automatic” mode very much like working with a personal trainer. By automating the resistance selection, the exercise machine can be programmed remotely (for example, from a personal computer or from the Internet). This allows the exercise machine to become part of a comprehensive regimen of diet and exercise, which may be planned by experts (or expert software). The exercise machine with programmable resistance capabilities also allows the actual performance of the user to be fed back to the regimen planner for follow-up modification or to display the actual execution in comparison with the original plan.  
           [0023]    To accomplish these and other objects an electronically selectable exercise machine has a coupling mechanism such as a handle connected to a cable at its proximal end arranged to transfer a resistance to a user of the electronically selectable exercise apparatus. The machine includes a lifting plate connected to the cable at its distal end and one or more sets of weights arranged in stacks. A motor-driven selector is provided which is arranged to engage one weight in each stack. Since the weights are stacked on each other, if the selected weight is lifted, all the other weights of that stack disposed above the selected weight are lifted simultaneously by the plate. The motor is located such that it does not move with the weights as the weights are raised or lowered. In a particularly advantageous arrangement, two sets of stacks are provided which are nested together to reduce space. The weights of each stack can reciprocate vertically along two guide rods.  
           [0024]    Each weight of each stack has an opening or cavity receiving one of the guide rods. A selector in the form of a cylindrical member is also disposed in this opening.  
           [0025]    The selector also includes two sets of lifting pins. The weights have tabs, each weight of a particular set having a uniquely oriented set of tabs. The selector has a set of unique angular positions, the number of positions being equal to the number of weights in a stack plus one. In each of its positions except one, the selector then engages the tabs of one of the weights. As the selector is lifted, it lifts with it the weight corresponding to the current position of the selector and all the weights disposed above that particular tab. The selector is rotated to a predetermined angular position when the stacks are at the bottom of the equipment. The rotation is accomplished by using stationary motors that may be controlled locally or remotely.  
           [0026]    The exercise machine has a programmable control unit in communication with the motors, and a display that is used to show the current weight setting of the machine and provide other data regarding the operation of the machine. The control unit further includes an input keypad to allow the input of a schedule of resistances provided to said users, and a network interface in communication with a computing system to record a user&#39;s progress in exercising and to calculate future exercise regimen. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    [0027]FIG. 1 is a side view of a weight lifting machine of this invention.  
         [0028]    [0028]FIG. 2 is a cut away plan view of the weight stack used in the machine of FIG. 1 taken along line  2 - 2 .  
         [0029]    [0029]FIG. 3 is a perspective view of the weight lifting machine of this invention.  
         [0030]    [0030]FIG. 4 is a cut away view of the weight stack of the machine of FIG. 1 taken along line  4 - 4 .  
         [0031]    [0031]FIG. 5 illustrates an enlarged perspective view of the weight stack and details of the selector mechanism.  
         [0032]    [0032]FIG. 6 is a top view of the secondary weight stack of this invention.  
         [0033]    [0033]FIG. 7 is a cut away view of the weight stack of FIG. 6 taken along line  7 - 7 .  
         [0034]    [0034]FIG. 8 illustrates the weight stack with one large weight plate and two small weight plates selected according to this invention.  
         [0035]    [0035]FIG. 9 illustrates the weight stack with five large weight plates and six small weight plates selected according to this invention.  
         [0036]    [0036]FIG. 10 is a block diagram of the electronic control and display circuit for the programmable weight lifting machine of this invention.  
         [0037]    [0037]FIG. 11 is a cross sectional view of a weight plate showing the lifting ring and lift tabs of this invention.  
         [0038]    [0038]FIG. 12 is a diagram of a lift tab of this invention.  
         [0039]    [0039]FIG. 13 is a perspective view of the weight selector of this invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0040]    [0040]FIG. 1 shows an exercise machine  100  of this invention incorporating a selectable weight stack  101 . The user pulls on handle  105  that is connected at the proximal end of a cable or similar elongated member  110  to the weight stack  101 . The machine  100  further includes a control unit  102  having a user display panel  103 . The control unit is connected to a drive unit (discussed in more detail below, in conjunction with FIG. 3) that is used to select the “weight” to be lifted. Usually, at least some of the weights of the weight stack  101  in accordance with a choice made by the user will be selected. However, where only minimal weight is desired, the user may select only the top plate of the weight stack and not the weights, per se.  
         [0041]    As shown in more detail in FIG. 3, the machine  100  includes a vertical post  106  with a longitudinal guide bar  119 . The post  106  supports a horizontal plate  108 . Plate  108  supports two pulleys  117 ,  118 . The machine  101  further includes a base  158  which supports the post  106  as well as two vertical guide rods  111 ,  112 .  
         [0042]    The weight stack  101  consists of weights which are selectively coupled to a plate  113  as discussed in more detail below. The stack  101  is arranged and constructed so that it is movable vertically up or down along the two guide rods  111 ,  112  and guide bar  119 . The cable  110  is trained over pulleys  117  and  118  and then passes through a hold in plate  108 . It then extends downwardly between the guide rods  111  and  112  and is attached to the plate  113  of stack  101  by a hook  114  at the distal end of the cable. As the user pulls on cable  110  with handle  105 , the cable  110  forces the plate  113  and any weights attached thereto to rise. Thus the force exerted by the user on the handle is determined by the number of weights attached to the plate  113  (as well as the weight of the plate  113  itself). As the user allows the handle to move back toward the plate  108 , the plate  113  and weights attached thereto are lowered toward the base  158 . Bushings  115  and  116  attached to plate  113  are provided and act as linear bearings, to reduce the friction between the guide rods  111  and  112  and the lift plate  113 , as the weight stack is raised and lowered.  
         [0043]    [0043]FIG. 2 provides a horizontal cross sectional view of the weight stack  101 , looking downwardly just below plate  113  and FIG. 4 shows a vertical cross sectional view of the weight stack  101 . As can be seen in these Figures, the weight stack  101  includes plate  113 , a set or plurality of vertically aligned outer weights  121  forming an outer weight stack, a set or plurality of vertically aligned inner weights  122  forming an inner weight stack and two selectors  141 ,  150 . The selectors  141 ,  150 , disposed in cavities or passageways in the weights (one such cavity or passageway being shown in FIG. 7), are used to selectively couple some or all of the outer and inner weights  121 ,  122  to the plate  113 .  
         [0044]    As seen more clearly in FIG. 2, each outer weight  121  has a round opening for a corresponding inner weight  122 . Both weights  121 ,  122  are free to move vertically, independently of each other, along rods  111 ,  112 . Both weights  121  and  122  are prevented from rotating about their respective vertical axes by guide bar  119 , guide notch  129  (formed in the inner weight  122 ) and guide notch  129 A (formed in outer weight  121 ). While the inner weights  122  are generally circular in shape, each outer weight has a somewhat oblong configuration, with straight sides  502  and curved ends  504  and  506 . End  504  defines a greater radius of curvature than end  506 . This shape advantageously presents a center of gravity for the weight at guide  111 , thereby preventing binding as the outer weights are raised or lowered about the guide.  
         [0045]    As seen in FIG. 4, selector  150  has at its top end a lip  128  which rests on bushing  116 . The bushing  116  is made of a low-friction material such as nylon, and allows the selector  150  to rotate freely with respect to the lift plate  113  and guide rod  112 . Selector  141  has a similar lip  115 A resting on bushing  115 . Bushing  115  is also made of nylon and allows the selector  141  to rotate with respect to the plate  113  and guide rod  111 . Lip  128  is positioned to abut the top surface of plate  113 . Accordingly, as plate  113  is raised by a user pulling on cable  110 , the plate lifts selector  150  which, in turn, allows the user to raise the weights selected by selector  150 .  
         [0046]    Details of the selector mechanism used to select the weights coupled to the plate  113  are now described in conjunction with the Figures. As shown in FIG. 13, the selector  150  consists of a cylindrical wall  150 A on which there are mounted an array of lift pins  142 . The array is partitioned into two sets of diametrically opposed pins  144   a  and  144   b . All pins  144   a  are vertically aligned and all pins  144   b  are vertically aligned along the surface  150 A as shown. In addition each pin  144   a  is aligned horizontally with a respective pin  144   b . The vertical spacing between the pins  144  in the array  142  matches the height of the weights  121 , 122  in the stack  101 .  
         [0047]    Each inner weight  122  includes a tab ring  125 . As shown in FIGS. 5 and 11 the tab rings  125  are press-fit into holes  121 A of the respective weights  122  from their respective underside. Due to a slight taper (shown somewhat exaggerated in FIG. 11), each ring  125  is wedged onto the respective weight  122 . Each tab ring is provided with two tabs  126   a ,  126   b  diametrically opposed to each other. The tab ring  125  defines a hole  126   c  for the selector  150 .  
         [0048]    When the selector  150  is inserted through the hole  126   c , two appropriately aligned lift pins  144   a ,  144   b  register with the tabs  126   a  and  126   b  on tab-ring  125 . Therefore, when the selector  150  moves up, it lifts the weight  122  with it through the tabs  126   a ,  126   b.    
         [0049]    [0049]FIG. 12 shows details of the tabs  126   a  and  126   b  of FIGS. 5 and 11. Tab  126   a  is formed of a structural material such as steel to be able to support the entire weight stack  101 . For example, this weight may be 300 lbs. or greater. To support the weight of the stack the lifting tab should have a width W 1  of approximately 1.5 times the diameter of the selector pin. For example, a 300-lb. weight stack requires a 0.250″ selector pin, thus the lift tab  126   a  is approximately 0.4″. To make the lift pins  144   a ,  144   b  self-securing, a seating notch  128  is formed in the lifting tab  126 . The seating notch  128  must be wide enough to accommodate any tolerances in the alignment of the selector pin. Therefore, the seating notch  128  should be at least 20% larger in diameter than the selector pin. In the case described above the width W 2  of the notch is approximately 0.3″ in diameter. The outer weights  121  are provided with identical tab rings and tabs to match lift pins on selector  141 .  
         [0050]    [0050]FIG. 7 provides a sectional view of inner weight stack  129  comprised of inner weights  122 , each inner weight  122  being nested in a corresponding outer weight  121  (see FIG. 2). As can be seen in FIG. 7, the tabs  126   a  of each inner weight  122  are angularly offset from each other.  
         [0051]    More specifically, when observed from the top, the tabs  126   a  and  126   b  on the inner weights  122  in the inner stack  129  are shifted 22.5 degrees from each other. If alignment of the tabs  126   a  and  126   b  in the top weight is assigned a reference angle of 0 degrees, then the second inner weight from the top will have its tabs  126   a ,  126   b  aligned at 22.5 degrees counterclockwise to the reference angle. The third weight is aligned at 45 degrees, and so on. Therefore, the seventh weight is aligned where the angle is 135 degrees.  
         [0052]    Because two tabs  126   a ,  126   b  are used in each weight, and these are 18 degrees apart, and if there is no eighth weight, the radial space between the seventh tab and 180 degrees is unused by any of the seven weights.  
         [0053]    Each pair of lift pins  144   a ,  144   b  (hidden under the tabs in the tab-ring  125 ) can engage one and only one of the tabs  126   a ,  126   b  as the selector rotates between 0 and 135 degrees. If the selector is set at 157.5 degrees, none of the weight will be engaged.  
         [0054]    Bearing in mind that any weight selected carries with it all the weights above it, it is clear that by rotating the selectors  141 ,  150  any one of the weights  121 ,  122  can be selected.  
         [0055]    An advantageous arrangement for the weight stack  101  is obtained if the outer weights  121  are 40 lbs. each, and if the inner weights  122  are 5 lbs. each. This arrangement allows a user to select any weight between 0 and 315 lbs., in 5 lbs. increments (ignoring the weight of the plate  113  and associated hardware, such as the selectors  141 ,  150 ).  
         [0056]    [0056]FIG. 8 shows the stack  101  with the first or top outer weight  121  selected, as well as the top two inner weights  122 . FIG. 9 shows the stack  101  with the top  5  outer weights selected, as well as the top  6  inner weights  122 .  
         [0057]    As shown in FIG. 4 and FIG. 5, the selector  150  is positioned on the guide rod  112  and is rotatable around bushing  116  (at the top) and bushing  162  (at the bottom). These bushings  116 ,  162  allow smooth vertical motion of the selector  150  on the stationary guide rod  112 , as well as low-friction rotation of the selector  150  with reference to the guide rod  112 .  
         [0058]    The bottom bushing  162  is designed to fit into and engage a dog clutch  152  . Thus when the selector  150  is at rest and is not pulled up by the lift plate  113 , it is locked rotationally by the dog clutch  152 . In this condition, the weights rest on stop pins  159  attached to the frame  158 . To reduce friction, the bushing  162  is coupled to the frame  158  through a ball bearing  156 , although other arrangements may be used. For example, ball bearing  162  may be replaced by a low friction bushing.  
         [0059]    The dog clutch  152  is coupled to a sprocket  153  which in turn is engaged to a worm gear  154 . Worm gear  154  is mounted on a drive shaft attached to an electric motor  155 . Thus, the sprocket  153  is driven by the motor  155  through the worm gear  154  to rotate in reference to the guide rod  112 .  
         [0060]    The electric motor  155  is adapted to turn the selector  150  freely through a full rotation, or more, without encountering any resistance other than the friction of the sprocket  153 , the bushing  116 , dog clutch  152  and the ball bearing  156 . Thus, while the selection is being made, none of the weights in the weight stack apply any force on the selector. Because the selection is “weight-free,” small stepper motors may be used. This not only decreases overall size and weight of the machine as a whole, but also decreases costs. Selector  141  for the outer weights is supported in an identical manner and is rotatable by a separate motor  160  (shown in FIG. 10).  
         [0061]    It should be noted that the motor, worm gear and sprocket are located in a position wherein these components are not moved, i.e., they are not lifted, as the weights are raised or lowered. Thus, there is no need for the motor to be mounted on the weights which is often deleterious to motor operation over many repetitions of the machine.  
         [0062]    Thus by rotating the selectors  141  and  150  one pair of lift pins  144  on each selector is placed under the lift tabs  126   a  and  126   b  of one of the weights  121 ,  122 . The selected weight(s) and all weight disposed upon the selected weight(s) from the weight stack  101  are coupled to the lift plate  113  through the respective selector  141  or  150 . When a user pulls on the cable  110 , the lift plate  113  and the selected weight(s) of the weight stack  101  are raised and lowered through an exercise cycle.  
         [0063]    The desired weight of the weight stacks  101  and  121  are selected in each stack by placing the selector at the desired rotational angle. This is achieved by energizing the electric motors  155  and  160  that are associated with each stack  101  or  129  for the proper length of time, so that each motor moves from its current position to the new position.  
         [0064]    The motors  155  and  160  in one implementation are servo motors that receive control signals indicating an amount of rotation necessary to select the desired weight from the weight stacks. The application and design of servomotors for such uses as shown are well known in the art and not discussed further.  
         [0065]    In a preferred implementation, the motors  155  and  160  are stepper motors such as model Z26440-12 manufactured by Haydon Switch and Instrument, Inc. This motor rotates 7.5 degrees for each pulse it receives. With the worm gear reduction set at 1:40 gear ratio, 120 pulses are required to rotate the sprocket  153  by 22.5 degrees. It is thus a simple matter to those schooled in the art of electronic control circuits to provide an electronic controller that will position each of the two selectors  141  and  150  at the desired weight selection.  
         [0066]    The selector  150  and the indexing sprocket  153  are locked rotationally only when the selector  150  is resting against the sprocket  153 .  
         [0067]    With reference to FIG. 5, sensor  161  is a proximity sensor mounted through bracket  162  mounted on frame  158 . The proximity sensor  161  is positioned so that it is within 5 millimeters from the bottom of the bushing  163 . In particular, the proximity sensor  161 , such as a proximity photo-microsensor EE-SB5 from Omron Electronics LLC, provides an output when a reflecting surface is within 5 millimeters from the face of the sensor. When the selector  150  is seated against the indexing sprocket  153 , the lower bushing  163  is lined up with the position sensor  161 . When the selector  150  is pulled up from its rest position, the bushing  163  is disposed away from the sensor  161  and the output of the sensor  161  indicates to the control circuitry (not shown) that the selector  150  is not in place and that the motor  155  should not be activated.  
         [0068]    By placing a notch in the lower bushing  153  at a height that is aligned with the position sensor  161  when the selector  150  is at its rest position against the indexing sprocket  153 , the “home” position of the sprocket  153  can be detected by the position sensor  161 . When the stepper motor  155  rotates the sprocket  153 , the output of the position sensor  161  is monitored. As the notch passes in front of the sensor  161 , the reflection from the surface of the bushing  163  is momentarily reduced due to the groove in its surface. The controller detects this change in the output of the position sensor  161 , and the “home” position is confirmed. The sensing of the “home” position is useful to prevent cumulative errors between the controller and the actual position of the sprocket  153 .  
         [0069]    A single-cable pull exercise system is inherently imbalanced. Because the ratio of the weights selected in the two stacks can be any combination of weights, it is not possible to locate the hook  114  to precisely compensate for this imbalance. In order to allow for a smooth operation of the weight stack, the bushings  116 ,  163  act to prevent the plate  122  from tilting under such imbalance conditions.  
         [0070]    [0070]FIG. 10 shows diagrammatically the electronic control unit  102  of the exercise machine of this invention. The control unit  102  is connected to the exercise machine  100  to provide selection signals to the motors  155  or  160  to select the desired weight from the weight stacks as described above. The position sensors  161  associated with selectors  141  and  150  transmit the position signals  215 ,  220  to the control unit  102  indicating the “home” position and “rest” position of each selectors  141  and  150 .  
         [0071]    The control unit  102  includes a microprocessor to receive the position signals  215  and  220  and generates encoded signals required to select the desired weights from the weight stacks. The microprocessor  200  contains a memory or storage device to retain an exercise regimen for one or more users. The microprocessor  200  is connected to motor driver  205  which receives from the microprocessor the encoded signals designating the weight to be selected. The motor driver  205  processes the encoded signals and generates the respective selection signals  225  or  230  that drive the motors  155  and  160  to select the desired weights. The selection signals  225 ,  230  cause the motors  155 ,  160  to rotate the selectors  141 ,  150  to place one pair of lifting pins  142  under the lifting tabs of the desired weight. Once a weight is selected in this manner, pulling on that weight automatically lifts all the other weights disposed that particular weight in the respective stack. It should be appreciated that the nesting of the two sets of weights allows the device to select one set of weights from each stack independently.  
         [0072]    The physical interface to the user is the user control panel  103 . The user control panel  103  as shown is exemplary. Generally, the control panel  103  has a keypad  235  or keyboard to act as an input device, such that the user can provide the desired weight amounts or program an exercise regimen. The control panel  103  has a display  240  (a three digit alphanumeric display in this example) to indicate the weight amount or regimen step.  
         [0073]    In operation, the user enters the desired weight on the keypad  235 . The display  240  shows the value of the weight just entered, in a flashing mode, while the motors  155  and  160  move the respective selectors to the desired positions. Once the selectors have reached the desired positions, the display  240  stops flashing.  
         [0074]    The three LED&#39;s  242 ,  244 ,  246  in the user control panel  103  are used to provide feedback to the user as to the status of the machine. The green LED  246  is lit when the machine is ready to be used for exercise. The yellow LED  244  is lit while the motor  155  and/or  160  is stepping the selector to a new setting or whenever one of the selectors is not in its rest position. The red LED  242  indicates an internal fault in the machine.  
         [0075]    The control unit  102  optimally may have a network interface  210  to allow communication of the microprocessor  200  to a personal computer  250  or with a communication network  255  such as the Internet. The network interface  210  allows updating of the program stored in the memory of the microprocessor. Alternately, the personal computer  250  or communication network  255  gives the necessary instructions to change the weights. This structure further allows a physical trainer or an expert system to direct and monitor multiple users through the network interface of multiple exercise machines.  
         [0076]    It will be appreciated that the weight lifting machine provides numerous advantages over the prior art. For example, it provides a weight stack that is compact, having a reduced footprint, yet one which nonetheless provides a broad range of weight selection. Selection of the weight is precise and errors in selecting the weight are minimized. The construction also provides smooth operation as the weights are raised and/or lowered.  
         [0077]    While this invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention. For example, while the embodiment shown describes an exercise machine in which weights are raised or lowered, it will be appreciated that the principles of the invention are applicable to other types of exercise machines in which various weights are selected by the user.  
         [0078]    One of the advantages of an electrically controlled weight stack is that the user may change the weights from different locations around the machine. In multi-function exercise machines, for example, the user may use a “lat” pull down where he faces the weight stack, and then switch to a leg extension where he faces away from the stack. As the exercise sets proceed, weights need to be changed (usually increased after each set), which would require getting up from the seat and reaching for the weight-selecting pin in a mechanical weight machine.  
         [0079]    It will be appreciated that the electronically controlled machine of the present invention advantageously may allow the use of a portable display/keypad that may be moved with the user, thus making the weight selection within reach at all times. Optionally, an RF link may be used between the display and the controller of the exercise machine. Such technology is readily available and can be used to replace a wired network, although it is contemplated that further advances in this technology will make such linkages even smaller (and perhaps worn by a user as a watch-like display) in the future.