Patent Publication Number: US-10307631-B2

Title: Electronically controlled mechanical resistance device for rowing machines

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of exercise equipment and more specifically to rowing machines. 
     BACKGROUND 
     Most state-of-the-art rowing machines allow oarsmen to simulate motions comparable to ones found when rowing in racing shells. To impart resistance to the rower&#39;s physical effort, some rowing machines deploy hydraulic rams (U.S. Pat. No. 5,104,363). However, the most successful ones, in terms of their ability to simulate rowing in boats, deploy an adjustable fluid pump. In certain embodiments, the pump moves air (U.S. Pat. No. 5,382,210) and in the other, the pump moves liquid water (U.S. Pat. No. 4,884,800). Regardless of the type of fluid, all said pumps comprise flywheels. The purpose of moving a fluid through a pump is to simulate an oar drag through water. The purpose of the integrated flywheel is to simulate a boat&#39;s inertia. 
     The beneficial effects of deploying flywheels on rowing machines relate to the flywheel absorbing the user&#39;s energy. Since the moment of inertia of a flywheel is constant, the added energy manifests as the flywheel&#39;s rotational motion. As this motion simulates that of a gliding boat, the torque resisting a rower suddenly changing the flywheel&#39;s rotational velocity is analogous to the force resisting a rower changing the speed of a moving boat. 
     The problem in using flywheels on rowing machines relates to how a rower applies his force to it. On other type of exercise devices, the combined user&#39;s motions tend to be synchronous to the moving flywheel. For example, peddling an exercise bicycle involves moving the feet in a circular motion, synchronous with its flywheel&#39;s rotation. In contrast, on a rowing machine, a rower engages the flywheel only during the power portion of the rowing strokes. Furthermore, at the beginning of the power phase of a stroke, the rower handle&#39;s velocity is zero, asynchronous to the already moving flywheel. 
     To engage the moving flywheel, a rower has to catch up to it at the beginning of the power phase of all but the first stroke during every practice. In addition, reconnecting with the moving flywheel becomes more difficult as the flywheel moves faster during more intensive exercise. In an effort to catch up to the flywheel, rowers tend to jerk their shoulders and forearms. The additional shoulder and forearm movement is not ideal and it is contrary to the proper rowing form. More importantly, rowing in such a way can also cause back injury. 
     In order to retain the flywheel&#39;s benefits and at the same time avoid its adverse effects, it is best to replace it with a more optimal device. To that end, this invention focuses on replacing not just the flywheel, but also the fluid pump comprising a flywheel. An embodiment of this invention comprises an electric motor/generator and the motor&#39;s control means. Alternatively, the motor can also be substituted with a linear acting solenoid. 
     Regardless of a given embodiment, the focus of this invention is to eliminate the need for rowers to catch up to the moving flywheel at the beginning of the power phase of every stroke. That is, the primary goal of this invention is to eliminate any backlash between the motion of the rower&#39;s handle and the motion of the resistance imparting device. The additional benefit of deploying electric motors or solenoids is that in certain embodiments, this invention can also produce the handle pressure into the back of the rower&#39;s palms, at the beginning of the power phase of a rowing stroke. This pressure is similar to the pressure experienced by rowers when rowing in real boats and inserting the oar blade into the moving water. 
     SUMMARY OF THE INVENTION 
     The primary goal of this invention is to eliminate the backlash that exists when exercising on state of the art rowing machines. This backlash is present between the idle and the power phases of rowing strokes and occurs on any common rowing machine that comprises a flywheel. It is hoped that this invention is used to substitute the flywheel integrated with other mechanical resistance means with a device comprising an electric motor/generator or a solenoid and a programmable control means. 
     By eliminating the backlash occurring on commonly used rowing machines, this invention allows the rowers to execute stress free rowing strokes. Stress free rowing leads to achieving better rowing technique, which translates to faster moving boats. Most importantly, better rowing technique contributes to significantly reducing the potential for rowers to sustain motion related injuries. 
     This invention can also produce the handle pressure into the back of the rower&#39;s palms, in the beginning of the power phase of rowing strokes. This pressure is similar to the pressure that a rower feels by rowing in a boat, while inserting the oar blade into the moving water. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an example of a prior art device. 
         FIG. 2  shows a basic embodiment of this invention, depicted in three dimensions. 
         FIG. 3  shows a basic embodiment in a two dimensional schematic, while emphasizing the details related to this invention&#39;s electronic controller. As depicted, the controller is used to manage a BLDC motor and control the motor&#39;s torque, which resists the rower&#39;s physical effort. 
         FIG. 4  shows a similar embodiment to that of  FIG. 3 . However, in addition to controlling the torque resisting the rower&#39;s physical effort, the controller is augmented to drivingly engage the attached BLDC motor. 
         FIG. 5  shows a basic embodiment in a two dimensional schematic. As depicted, the controller manages a DC motor and controls the motor&#39;s torque resisting the rower&#39;s physical effort. 
         FIG. 6  shows an augmented  FIG. 2  embodiment. The three dimensional drawing relates to the two dimensional schematic shown in  FIG. 4 . In addition to the basic functionality of providing the resistance to the rower&#39;s physical effort, the depicted embodiment comprises a spring that allows the device to push the handle into the back of the rower&#39;s palms, at the beginning of the power phase of rowing strokes. 
         FIG. 7  shows an alternate embodiment in a two dimensional schematic. As depicted, the controller manages a solenoid and controls the solenoid&#39;s resistance to the rower&#39;s physical effort. 
         FIG. 8  depicts a three dimensional embodiment corresponding to the two dimensional schematic shown in  FIG. 7 . 
         FIG. 9  shows an augmented  FIG. 7  embodiment. In addition to the basic functionality of providing the resistance to the rower&#39;s effort, the depicted embodiment allows this invention to push the handle into the back of the rower&#39;s palms, at the beginning of the power phase of rowing strokes. Conceptually, this embodiment provides the same functional addition as the embodiment shown in  FIG. 6 . 
         FIG. 10  shows a detail pertaining to the drawing shown in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This invention is intended to replace a common mechanical resistance device on rowing machines. An example of a prior art device is shown in  FIG. 1 , where system  1  is an air pump. The rotating parts comprise the flywheel  2  and a multitude of air peddling vanes  3 , perpendicularly disposed and rigidly affixed to the flywheel&#39;s largest surface. The mechanism also includes a valve, comprising the stationary and the adjustable components. The stationary components of the valve are the safety shroud  4  and the face plate  5 . Together, they envelop the rotating pump parts, forming a cavity in which the air peddling vanes  3  move the air as the flywheel rotates. The face plate  5  is perforated. It is disposed centered and parallel to the flywheel  2 . It also shields the air peddling vanes  3  from accidental contact with objects outside of the pump. Since the valve cover  6  is also perforated, its rotation on top of the perforated faceplate  5  causes different interference openings between the two. A user rotates the valve cover  6  to adjust the system&#39;s pumped air throughput. The more air the system pumps, the higher is its resistance to the rotation and vice versa. To lock the valve cover, a user inserts pin  7  through one of the locator holes  8 - 17 . 
     An embodiment of this invention is shown in  FIG. 2 . The inner diameter cylindrical surface of the one way clutch  21  couples to the motor&#39;s shaft  22  and the outer diameter surface rigidly couples to the bored hole of the timing pulley, or a sprocket,  23 . Said one way clutch drivingly engages said pulley and the motor&#39;s shaft  22  only during the power phases of rowing strokes. The timing belt, or a chain,  27  drivingly couples to said timing pulley  23 . One of the timing belt&#39;s ends attaches to the rower&#39;s handle  28  and the other attaches to the recoiling mechanism  29 . The handle movement following the direction of vector  101  uncoils said timing belt  27 . Its movement in the opposite direction, following vector  102 , causes said timing belt, or a chain,  27  to recoil. Vector  101  coincides with the direction of the handle&#39;s motion during the power phase of rowing strokes and vector  102  coincides with the handle movement during the idle phase of rowing strokes. Said recoiling mechanism  29  and said motor  24  are rigidly affixed to the rowing machine and said motor/generator  24  also attaches via the wiring harness  25  to the motor control means  26 . 
     The invention&#39;s general function is to provide a mechanical resistance countering the rower&#39;s physical effort. This resistance manifests as torque on said motor&#39;s shaft  22 . The combination of said timing pulley  23  and said timing belt  27  convert the torque from the motor&#39;s shaft to the linear force, transmitted to the rower&#39;s handle. The force resists the linear and mainly horizontal motion of said handle  28 , during the power phase of rowing strokes. During the idle phase, the recoiling mechanism  29  maintains the tension on said timing belt  27  and helps the rower move said handle  28  in the opposite direction. 
     In contrast to said legacy device ( FIG. 1 ), where the torque resisting its rotation is dependent on the rotational velocity of its comprising flywheel  2 , the new device (ND), shown in  FIG. 2 , is capable of producing a full range of torques at any rotational velocity of its comprising motor. By controllably managing the torque output of the motor&#39;s shaft, the ND can produce a custom set of torque responses corresponding to a set of rower handle&#39;s velocities. 
     To achieve instantaneous torque adjustment, the ND rapidly shorts and opens its motor winding&#39;s leads. Shorting and opening the motor windings effectively manages the motor&#39;s induced currents. In order to toggle similar currents several thousand times per second, said motor control means  26  must comprise at least one microcontroller or an equivalent. The microcontroller provides the control signal to the gate of at least one power transistor, which switches the current, or the combined currents generated by the motor windings. The microcontroller&#39;s control signal affecting the gate of said power transistor comprises on/off square pulse cycles, which in the art of electronic engineering is referred to as Pulse Width Modulation (PWM). In constructing a ND, the requirement is that a selected said power transistor must be capable of toggling currents and voltages comprising power comparable to the maximum power output of any rower. The same applies for a selected motor, which also must be capable of handling at least the maximum power output of a rower. 
     Depending on a given requirement, the ND implements torque adjustments from several times to a few hundred times per second. For example, while a rower&#39;s handle is at rest, there is no need to adjust the torque rapidly. However, when a rower is pulling said handle  28  ( FIG. 2 ) during the power phase of rowing strokes, the torque needs adjustment at least one hundred times per second. In a typical scenario, the ND&#39;s microcontroller  51  ( FIG. 3 ) signals the ‘shorting’ power transistor  39  to toggle the generated motor current at above audio range frequencies. Selecting above audio range frequencies relates to avoiding noise pollution caused by these frequencies resonating in said motor&#39;s cavity. A precise torque adjustment can be accomplished by instantly varying the pulse width ratio between the ‘on’ and the ‘off’ portions of the switching PWM cycles. 
     An embodiment of a ND can comprise several motor types, most notable of which are the brushless DC (BLDC) and the brushed DC motor. In the embodiment of  FIG. 3 , said motor  24  is a multiphase BLDC. In addition to said ‘shorting’ power transistor  39 , the power section of this embodiment&#39;s controller  35  also comprises a rectifying section  36 , employing a multiphase diode H-bridge. This section combines and rectifies the generated AC currents from said motor/generator  24 . The power section of said controller  35  further comprises filter  37 , which smoothes the rectified and summed current. In turn, said ‘shorting’ power transistor  39 , switched by the microcontroller  51 , controllably toggles the smoothed current. Also, the power section  35  comprises the startup resistor  38 . This resistor attaches in parallel to the ‘shorting’ power transistor  39  and it is responsible for providing resistance to the motion of said handle  28  while the controller  26  is inactive. The purpose of limiting this motion is to limit the induced voltage in said motor  24 , thereby protecting the ‘shorting’ transistor  39  from over voltage damage. 
     The ND&#39;s controller also comprises a large capacitor  41  ( FIG. 3 ), used to store the induced charge from the motor&#39;s windings. Said capacitor  41  connects in parallel to said ‘shorting’ power transistor  39 . The ND harnesses the charge during the ‘off’ portions of said PWM cycles. As said ‘shorting’ transistor  39  disengages from shorting the motor&#39;s windings  29 ,  30 ,  31 , the impedance across the charging capacitor becomes less dominant, compared to the infinite impedance of the open circuit set by the transistor  39 . This allows the majority of the induced current to flow through the charging capacitor  41 . As the ‘shorting’ transistor  39  shorts said motor&#39;s windings  29 ,  30 ,  31  (PWM on portion), the short circuit&#39;s impedance becomes the least dominant. This makes the majority of the induced current bypass the charging capacitor  41 . The ND uses the stored charge to recharge its own battery pack  50 , allowing it to be independent of an external charge supply. The battery pack  50  allows the controller to remain active during the sleep and the startup phases of operation. The excess energy can also charge an external power-consuming device. 
     To charge its battery pack, the ND also comprises the battery charging means  48  ( FIG. 3 ). Through this apparatus, the battery pack  50  consumes the energy from said charge harnessing capacitor  41 . The charging means  48  attaches to said charging capacitor  41  through the voltage divider  43 . A detailed description of the charging means  48  is omitted as current state of the art inexpensive circuitry performing similar function is readily available. 
     In the embodiment of  FIG. 4 , motor  24  is once more a multiphase BLDC. However, the rectification section  36  also comprises multiple power transistors  57 - 62 . Each transistor is disposed in parallel to each diode comprising the multiphase H-bridge  36 . The transistors are attached so that the poles of their flyback diodes align with the poles of the diodes comprising the H-bridge. The additional power transistors  57 - 62  allow the controller to drivingly engage the motor&#39;s shaft. In order to move the motor, the ND&#39;s controller must commutate the forward driving current through said multiphase bridge  36 . To commutate the current, the ND must obtain the position of the motor&#39;s windings  29 ,  30 ,  31  with respect to the motor&#39;s magnetic poles. Hence, in this embodiment, the ND also comprises sensor, or sensors,  32  that detect the absolute position of its motor&#39;s shaft. In order to draw charge from said charging capacitor  41  back into the motor, the embodiment of  FIG. 4  also comprises the charge feedback circuit  53 . This circuit further comprises the forward feedback transistor  55 , the blocking transistor  56  and the diode  54 . The forward feedback transistor  52  discharges the charging capacitor  41  into the rectifier  36 , and the blocking transistor  53  decouples the fed back current from the charging capacitor  41 . Said diode  54  ensures that the current in the feedback circuit  53  always flows in one direction, which is into the rectifier  36 . 
     In the embodiment of  FIG. 5 , the combination of the microcontroller  51 , or its equivalent, and the ‘shorting’ power transistor  39  toggle the induced currents coming from a brushed DC motor  24 . Since the generated current is direct, there is no need to rectify or filter it. Therefore, unlike the embodiment of  FIG. 3 , the power section  35  of  FIG. 5  comprises neither a rectifier nor a filter. Also, similar to the embodiment of  FIG. 3 , in this embodiment, the ND does not drivingly engage the motor  24 . 
     In general, the ND controls the motor&#39;s torque based on instantaneous system requirements. The instantaneous adjustment of the motor&#39;s torque is only required during the drive portion of a stroke. Similar adjustment is not necessary during the recovery phase of a stroke. In order to detect whether a rower&#39;s handle is in the recovery or in the drive phase, the ND must also comprise sensors similar or equivalent to a rotary quadrature encoder  33  ( FIG. 3 ) coupled to said timing pulley  23 . Said encoder  33  attaches to said microcontroller  51  through the wiring harness  34 . The underlying requirement of implementing this encoder, or similar, is that said microcontroller  51 , within any given millisecond interval, must be aware of the change in position and the motion direction of the rower&#39;s handle  28  ( FIG. 2 ). Since the handle is coupled to said pulley  23 , detecting the change of position of said pulley  23  over a millisecond interval is sufficient. 
     The component that makes this invention unique is the algorithm managing its resistance imparting device. A major goal of this algorithm is to ensure that at the beginning of the power phase of a rowing stroke, the velocity of the rower&#39;s handle is not out of sync with the velocity of the resistance imparting device. Under optimal conditions, as the handle approaches the drive/power phase of a stroke, and before the rower&#39;s handle completely stops, the ND sets the motor shaft&#39;s rotational velocity to zero. In order to slow down the motor in due time, the ND detects the transition between the end of the drive and the beginning of the recovery phase of a stroke. To determine this information, it relies on said encoder  33  ( FIG. 3 ). Immediately after the recovery phase begins, the ND attempts to lock the motor&#39;s shaft by putting emphasis on shorting the motor&#39;s windings  29 ,  30 ,  31  ( FIG. 3 ) within said switching PWM (on/off) cycles. At the beginning of the power phase of a rowing stroke, slowing down the motor shaft&#39;s velocity to zero equalizes its speed to that of the rower&#39;s handle. The synchronization between the two provides a prerequisite for avoiding backlash between them. The ND almost completely avoids said backlash by also setting a relatively high level of torque on the motor&#39;s shaft during the synchronization. In a worst-case scenario, if there is insufficient time to stop the motor completely (before the handle velocity reaches zero), the ND minimizes the motor shaft&#39;s rotational velocity. Although some backlash may remain, slowing the motor down minimizes it. For the first instance of the power portion of a stroke, the ND holds a constant torque at a maximum useful torque level. As the handle  28  ( FIG. 2 ) starts moving into the drive phase, the ND rapidly diminishes the torque level, but only for the first fraction of a stroke. Throughout the rest of the drive/power phase, the ND progressively varies the torque with the handle velocity. 
     In the embodiment of  FIG. 4 , the ND also uses the stored charge to drivingly engage the motor. As a rower exercises at higher stroke per minute rates, during a stroke&#39;s recovery phase, there may be instances when the rower moves the handle  28  ( FIG. 2 ) faster than the velocity of the handle tensioned solely by said retracting mechanism  29 . The velocity mismatch develops a slack in said timing belt  27  and can potentially uncouple it from the timing pulley  23 . The ND&#39;s controller anticipates a similar condition by monitoring the handle&#39;s acceleration using said encoder  33  ( FIG. 3 ). During similar instances, if there is sufficient charge in said charging capacitor  41 , the ND drivingly engages the motor  24 , providing additional tension to the timing belt  27  ( FIG. 2 ). Alternatively, the ND may drivingly engage the motor  24  an instant after the handle slows down to zero. The engagement occurs subsequent to the beginning of the drive phase of a stroke. The purpose of this engagement is to create a positive tension between the handle  28  and the rower&#39;s shoulders. This tension is beneficial as it promotes rowing with proper posture. 
     In the embodiment of  FIG. 6 , the ND also comprises a compression spring  63  that the handle  28  engages at the last portion of the stroke&#39;s recovery phase. Said spring is also affixed to the rowing machine. In addition, this embodiment comprises said multiphase H-bridge arrangement of the power transistors  57 - 62  ( FIG. 4 ), as well as said feedback circuit  53 . As the handle  28  ( FIG. 6 ) engages the spring  63 , the ND&#39;s controller drivingly engages the motor  24 , which in turn compresses the spring  63 . Eventually, the controller halts the handle, locking the spring in a compressed position. Immediately after, the ND&#39;s controller  51  ( FIG. 4 ) releases the spring. To control the spring&#39;s rebound, the ND&#39;s controller partially engages the ‘shorting’ power transistor  39  and fully disengages said feedback circuit  53  and the rectifier disposed power transistors  57 - 62 . The rebounding spring pushes the handle into the back of the rower&#39;s palms, which mimics the oar handle&#39;s motion produced by rowing in a shell, while inserting the oar blade into the moving water. As the handle  28  moves further toward the rest of the drive, the ND switches to the mode of progressively adjusting the motor&#39;s torque with the handle velocity. In order to detect the contact of the rower&#39;s handle  28  ( FIG. 6 ) to the spring  63 , a similar embodiment also comprises an accelerometer on the body of the rowing machine or on the rower&#39;s handle  28 , and a microcontroller algorithm which can detect the signature of the spring motion as the handle engages said spring. Said algorithm comprises accelerometer signal&#39;s peak detection while the handle position is known to be in the vicinity of the front end of the stroke. 
     In the embodiment of  FIGS. 7 and 8 , the combination of said BLDC motor and said one way clutch can also be replaced by the solenoid  64 . As in the case of the embodiment of  FIG. 5 , the rectifier and the filter of the power controller&#39;s section  35  become superfluous. Said solenoid  64  ( FIG. 8 ) drivingly engages the rower&#39;s handle  28  through the three joints  66 ,  68 ,  70 , two piece scaffolding. 
     Said scaffolding comprises the bottom  67  and the top  69  rigid legs. The bottom scaffolding leg joint  66  is affixed to the rowing machine and it allows the bottom leg  67  to pivot around its bottom tip on a parallel plane constraining the motion of said timing belt  27 . The middle scaffolding joint  68  couples the other tip of the bottom leg and the bottom of the upper scaffolding leg  69 , and allows both legs to pivot with respect to one another on said plane, parallel to the plane constraining the motion of said timing belt  27 . The top scaffolding joint  70  perpendicularly couples the rower&#39;s handle  28  to the top tip of the upper scaffolding leg  69 , allowing the handle to rotate around its longest axes. Said solenoid  64  couples to the linear bearing block  71 , wherein said linear bearing block slides longitudinally along said bottom scaffolding leg  67 . Said solenoid  64  is tangentially disposed over said bearing block&#39; largest surface, wherein said bearing block&#39;s surface is the one facing away from said bottom scaffolding leg  67 . Said solenoid&#39;s housing has a cylindrical tab  73  ( FIG. 10 ), which is perpendicularly affixed to the center of the largest cylindrical surface of the solenoid. This tab mates with the hole  74  in the center of said bearing block  71 , wherein said hole is cylindrical and perpendicular to said bearing block&#39;s largest surface. The mated joint allows said solenoid to pivot around the center of said bearing block&#39;s largest surface. The solenoid&#39;s magnetic core rod  65  ( FIG. 8 ) is affixed to the rowing machine through joint  73 , allowing said solenoid to move longitudinally along said bottom scaffolding leg  67 . 
     As in the embodiments comprising said motor/generator  24  ( FIG. 2 ), said solenoid provides resistance to the rower handle&#39;s motion. However, unlike the embodiments associated with rotating motors, this embodiment does not require any synchronization adjustments between the rower&#39;s handle and the resistance imparting mechanism. As shown in  FIG. 9 , the solenoid based embodiment can further be augmented with the controller that can drivingly engage said solenoid. As in the case of the embodiment of  FIG. 4 , the power section of the controller  35  shown in  FIG. 9  comprises a charge feedback circuit  53 . This circuit allows the charge stored in said charge storing capacitor  41  to be fed back to the resistance imparting mechanism, which in the case of the embodiment of  FIGS. 8 and 9  is the solenoid  64 . As in the case of the embodiment of  FIG. 6 , the ND causes the solenoid to move the handle at the beginning of the drive phase of a rowing stroke, causing the handle to push the back of the rower&#39;s palms. As stated, a similar pressure is experienced by rowers when rowing in real boats and inserting the blade into the moving water. 
     Finally, in any of the discussed embodiments, said motor/generator/solenoid control means  51  also comprises a means to connect it to an auxiliary computer  20 . Said auxiliary computer obtains the data related to all discussed algorithms, and calculates the various workout display parameters from said data, such as rower&#39;s power consumption, traversed distance etc. Furthermore, the auxiliary computer can also input parameters back to the microprocessor  51 .