WO1989011314A2

WO1989011314A2 - Exercise machines

Info

Publication number: WO1989011314A2
Application number: PCT/GB1989/000550
Authority: WO
Inventors: Andrew Clive Michell; John Burch; Peter Duthie
Original assignee: R.A.T. (Manufacturing) Limited
Priority date: 1988-05-20
Filing date: 1989-05-19
Publication date: 1989-11-30
Also published as: WO1989011314A3; GB2219410A; GB2219410B; AU3575689A; GB8811924D0

Abstract

A rowing exercise machine is arranged so that each stroke causes rotation of a flywheel and the shaft of an alternator. The resistive forces are primarily provided by the alternator which is driven by a constant but adjustable current. In the intervals between strokes, the deceleration of the flywheel is measured to provide an indication of the resistive forces being generated by the machine. This measurement is used to control the forces and/or to provide an indication of the work carried out by the user.

Description

EXERCISE MACHINES

This invention relates to exercise machines, and is particularly but not exclusively concerned with rowing machines. Exercise machines of this type are well known and widely used. Attempts have been made to provide such machines with a mechanism which responds to the user's activities in a manner which simulates actual rowing. For example, US Patent 4674741 and EP-A-0214748 disclose a machine which is said to simulate the "feel" of actual rowing by electronically controlling a brake to apply a constant torque to oppose the movement of a flywheel which is rotated by the force of the user's activity, the torque being independent of the rotational velocity of the flywheel. However, this arrangement would not provide a true simulation of the "feel" of actual rowing, as is commonly desired.

Another problem with known exercise machines both of the rowing type and of other types is that the response characteristic of the machine, that is the amount of energy required to operate the machine, is not accurately predictable or repeatable. For example, although a machine may be adjustable so that it has different settings corresponding to different amounts of energy required to operate the machine, the amount of work required of the user at a particular setting would vary from machine to machine, and from time to time with the same machine. This means that users cannot set the machine so that a known amount of work is carried out by the user. Nor can they accurately monitor their progress or compare their abilities with each other.

This is exemplified by the prior art referred to above, in which the level of a signal for controlling brake force is determined by a processor, and may for example be a constant or be dependent on the speed at which a user operates the machine. This level is also used in a formula for calculating an indicated measure of expended calories. However, the actual braking force generated by a signal of a particular level would vary, and the machine efficiency would also vary, whereas in the prior art it is assumed to be a constant. For this reason, force control and indicated energy expenditure would be inaccurate.

According to a first aspect of the invention there is provided an exercise machine in which the resistance to the work performed by the user is provided at least in part, and preferably substantially entirely, by an electrical machine, such as an alternator or dynamo, in which the exciting field is of a substantially constant magnitude. This, it has been found, provides a response from the machine which exercises the user better, which the user finds more satisfactory, and which in a rowing exercise machine simulates more accurately the response achieved in actual rowing. It is believed that this is a result of the resistive force acting against the user being substantially proportional to the speed at which the exercise machine is operated. The exciting field is preferably provided by one or more windings carrying a substantially constant current. Preferably, the current is adjustable to provide different degrees of resistance. Alternatively, the exciting field could be produced by permanent magnets, and adjustability could be achieved by providing a variable resistance across the output windings of the electrical machine.

In accordance with another aspect of the invention there is provided an exercise machine having means for sensing the degree of at least part of the resistance presented to the work performed by a user so as to provide a signal indicative thereof for either controlling the resistance or providing an indication to the user in response thereto. In a particularly preferred embodiment of the invention, the machine has an inertial mechanism, preferably a flywheel, which is intermittently driven by the user during operation of the machine, and the means for sensing the degree of resistance is operable to determine the decrease in speed of the mechanism in an interval between times at which it is driven by the user.

The above arrangement thus provides a signal which can be used to compensate for variations in the degree of the resistance, either by altering the resistance or altering an indication thereof. For this purpose, it is not essential that the signal accurately represent the entire resistance. It is desired merely that the sensing of resistance be done in a consistent manner and take into account that part of the resistance affected by the particular mechanical and electrical tolerances of the machine, as these are the factors which tend to vary from time to time and from machine to machine. If desired, a calibration operation could be effected to determine approximately the relationship between the value of the signal and the actual resistance presented by the exercise machine.

The degree of resistance presented to the user may vary during the operation of the machine, e.g. in proportion to the speed of operation. It is preferred that such resistance variations be taken into account. However, it is not essential that these variations be monitored, so long as they are reasonably predictable. Thus, for example, by assuming or calculating the form of a relationship between the speed of the flywheel and the degree of resistance presented to the user, and by monitoring the speed of the flywheel both while it is being driven by the user and in the intervals between being driven, it is possible to calculate a value which accurately represents the work being carried out by the user.

By way of example, if the resistance is provided by an alternator or dynamo driven by a constant current, in accordance with the first aspect of the invention mentioned above, and if it is assumed that the degree of resistance presented to the user varies in proportion to the speed of the flywheel, then by measuring the deceleration of the flywheel over a particular speed range in the interval between the time at which it is driven by the user, it is possible to predict the resistance presented at other flywheel speeds. Consequently, by monitoring the speed of the flywheel it is possible to calculate the work being carried out at any given instant, and by integrating this value over one cycle of operation, the total amount of work carried out during that cycle can be calculated and indicated. In an alternative embodiment, deceleration of the flywheel is measured at a plurality of different speed ranges and the results stored, so that during use the flywheel speed can be detected and the corresponding resistance looked-up for use in controlling the degree of resistance or providing an indication to the user of the work being carried out.

The resistance may be provided by any electrically-operated braking means, such as an electro-mechanical or electro-magnetic brake, but is preferably provided by an alternator or dynamo. The signal derived from the sensing means may be used to control the braking means so as to determine the degree of braking so that the detected resistance matches a predetermined value. In this way, it can be ensured that different machines, and the same machine at different times, can give substantially predictable and repeatable responses.

It may be desired in some circumstances for the degree of resistance to be controllably altered as the user operates the machine, e.g. throughout the user's stroke if the machine is a rowing machine. For example, in an arrangement in which an alternator or dynamo provides the resistance and, at any given time, is driven at a substantially constant current, a control circuit of the machine may be arranged to alter the level of that current in a predetermined manner (preferably as a function of speed) during the stroke.

Preferably, the machine has different settings, so that the sensed resistance can be controlled to match a plurality of different desired values.

In addition or as an alternative to this control technique, the signal indicative of the degree of resistance may be used to provide a substantially accurate indication of the amount of work being expended by the user. This could be in the form of a simple indication dependent upon the current sensed resistance, or the signal can be processed, e.g. by integration over the course of a cycle of operation as mentioned above. Alternatively or additionally, processing can be carried out so that the indication represents the total amount of work expended during the course of a work session.

An arrangement embodying the invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a schematic perspective view of an exercise machine in accordance with the invention;

Figure 2 is a plan view to illustrate the function of the mechanical parts of the apparatus;

Figure 3 is a side elevation of the parts shown in Figure 2;

Figure 4 is a schematic block diagram of a control circuit of the machine; and

Figures 5a, 5b, 6 and 7 are flow charts indicating the way in which the circuit operates.

Referring to Figures 1 to 3, the rowing machine 2 has a seat 4 mounted for movement along a frame 6, and arms 8 which can be drawn rearwardly by a user on the seat 4 with his feet on rests 10. The arms are attached to a rope 12 which extends around pulleys 14 and 16 to a reel 18 mounted on a chassis 20 supported beneath the frame 6. As will be explained, the reel 18 is spring-biased so that after the rope 12 has been unwound from the reel 18 as the user draws back the arms, the reel tends to wind up the rope and therefore draw the arms 8 back to their original position. The user operates the machine in the usual way, expending energy in order to draw back the arms against the resistive force provided by a mechanism described below, and then permitting the arms to be drawn back to their original position.

One feature of the present embodiment is the use of the rope 12, as distinct from the chains and cables conventionally used. This is wound uniformly over the reel 18, and enables a smoother operation of the machine. However, other elongate members, such as chains or cables, could alternatively be used.

The reel 18 has a shaft 22 coupled via a belt 24 to a pulley 26 on the end of a cylinder 28 carrying a helical spring 30. In Figure 2, part of the spring 30 is omitted to reveal the cylinder 28. As the rope 12 is unwound from the reel 18, the belt 24 causes the pulley 26 to rotate, thus winding up and tensioning the helical spring 30, which is attached at one end to the chassis 20 of the machine and at the other end to the pulley 26. Thus, when the user permits the arms

8 to be retracted, this is achieved by the spring 28 rewinding the reel 18 via the belt 24. The spring force is very small, and is negligible in comparison with the resistive force applied against the user when he pulls the arms rearwardly.

This resistive force is provided by an alternator 31 mounted on the chassis 20 and having a rotor (32 in Figure 4) mounted on a shaft 33 coupled to the takeup reel 18 via a belt 34, which extends around a relatively small diameter pulley 36 on the alternator shaft 33 and a large-diameter pulley 38 on the shaft 22 of the reel. The alternator shaft 33 also carries a flywheel 42.

Thus, as the arms 8 are pulled back by the user, the flywheel 42 and alternator rotor are caused to rotate very rapidly due to the gearing-up effect of the pulleys 36 and 38. This means that the flywheel may be lighter than would otherwise be required. A conventional one-way clutch (not shown) allows the flywheel and rotor to continue to rotate as the spring 30 rewinds the rope 12 at the end of the stroke.

The flywheel 42 is provided with notches 44 in its periphery. An optical sensor arrangement 46 (e.g. comprising an LED 48 and a phototransistor 50 as indicated in Figure 4) is mounted such that as the flywheel 42 rotates the notches 44 pass the sensor 46 in succession. The sensor arrangement thus provides pulses at a rate dependent upon the flywheel speed.

Referring to Figure 4, the alternator is of the type in which the rotor 32 provides the exciting field in response to direct current supplied through slip-rings (not shown) . The output from the stator 52 is rectified, and dissipated through a resistor 54. In the present embodiment the rotor is driven with a substantially constant current. The interaction between the rotor and stator fields provides the main resistance to the pulling of the arms.

The circuit shown schematically in Figure 4 comprises a computer/display section 100, and a power section 102 which includes the alternator and the sensor 46. The section 100 includes a microprocessor 104 (e.g. a Zilog Z86C91) coupled in a conventional manner via address/data buses to a ROM 106 storing the operating program of the microprocessor, a non volatile read/write memory 108, a digital to analog converter 110, input/output interfaces 112 and 114, and a display driver 116 which is in turn coupled to a display unit 118. The sensor 46 and user-operable switches 120, 122 and 124 are coupled to the microprocessor 104 via the input/output interface 114, and may, for example, be arranged to operate interrupt terminals of the microprocessor. The display unit 118 and switches 120, 122 and 124 are located in proximity to the user, e.g. as shown in Figure 1. The microprocessor is operable to cause the display driver 116 to display desired information, such as that described below, on the display 118. The microprocessor 104 also delivers a LOAD signal to the digital to analog converter 110, which will control the degree of resistance being produced by the alternator. The section 100 has a low-capacity battery (not shown) for permanently supplying power to the microprocessor 104 and the. non-volatile memory 108. However, during normal use, the main power for the section 100 is derived from a battery 130, which supplies the power on a line 132 under the control of a control circuit 134. The microprocessor 104 can control the operation of the control circuit 134 via the input/output interface 112.

In the power section 102, the battery 130 also supplies power to the rotor 32 of the alternator. The degree of power supplied is controlled by a voltage-controlled current regulator 136. This causes a constant current level to flow through the windings of the rotor 32, the magnitude of the current being dependent upon the control voltage received on line 138 from the digital to analog converter 110, and thus on the value of LOAD. The voltage generated by the alternator is also supplied to a battery charging circuit 140, which enables the battery 130 to be charged and which is also capable of delivering on line 142 a signal indicating that the battery level is low.

All the components of the circuit shown in Figure 4 are of a well known type, and the function of each individual illustrated block can be achieved by interconnecting components in a manner which is well known per se. The operation of the circuit will now be described with reference to Figures 5a, 5b, 6 and 7. Figures 5a and 5b represent the main program loop executed by the microprocessor 104. Figures 6 is an interrupt routine which is triggered each time a pulse is generated by the sensor 46, whereby the main routine is interrupted, the program represented by the flow chart of Figure 6 is executed, and then the main routine is re-entered. Figure 7 is also an interrupt routine, but in this case this is initiated at regular intervals as determined by an internal timer of the microprocessor 104. In the illustrated embodiment, the routine of Figure 7 is executed every

2.5 mS. The operation will first be described with reference to Figures 5a and 5b, but it should be noted that the following flags and values are caused by the interrupt routines to be stored in predetermined memory locations for use by the main program loop:

(a) A value RATE, which represents the last-measured interval between the time at which the flywheel speed was equal to a predetermined value Si and the time at which it had dropped to a lower value S2, during an interval between strokes performed by the user. This value RATE therefore is indicative of the current value of the resistance being presented to the user by the rowing machine, including the resistance presented by the alternator and other forces, particularly friction.

(b) An ACCEPT flag, which indicates that the flywheel speed has just decreased over a range including the speeds SI and S2 , so that a calibration operation can be carried out. (c) An END-STROKE flag, which indicates that the user has just completed a stroke.

(d) A BAR-TOTAL count. As will be explained, the display unit 118 includes a bar graph display, and the microprocessor 104 is arranged to output a BAR-GRAPH value at regular intervals, to cause the display to indicate a level represented by the BAR-GRAPH number. All the BAR-GRAPH values outputted during a stroke are accumulated, to form BAR-TOTAL. (e) A value BAR-COUNT, which represents the number of BAR-GRAPH values added together to form BAR-TOTAL.

(f) A value WORK representing the amount of energy expended by the user, or an amount used to calculate this energy in the manner explained below.

(g) A value STROKE-LENGTH indicative of the duration of the last stroke executed by the user.

Referring to Figure 5a, when the circuit is initially turned on or reset at step 500, the program proceeds to step 502. Here, various initialising operations are carried out, including initialising stored variables, and initialising the signals supplied to the display driver circuit 116.

Then, at step 504, the program checks to determine whether all three of the switches 120, 122 and 124 are pressed. If so, the program enters a special mode at step 506, wherein the total use of the machine since it was first supplied is indicated. This can be in the form of an indication of the number of strokes, the total effective distance rowed, and/or the total energy expended in operating the machine.

At step 508, the program checks to determine whether the switches 120 and 124 only are simultaneously operated. If so, the program proceeds to step 510, which is another special mode in which a RANGE variable is set to zero. RANGE represents the setting of the machine, higher values corresponding to greater degrees of resistance. When RANGE is set to zero, no energy is supplied to the alternator, so that the resistance is formed merely by the frictional resistances of the machine.

At step 512, the program checks for other key presses, and executes appropriate sub-routines depending upon which of the switches are operated. In this way, the user can operate the switches 120, 122 and 124 to set different modes of operation of the machine, using switch 120, and increase or decrease stored variables, using switches 122 and 124, respectively. The user can set the value of the variable RANGE, can determine whether the machine should operate for a preset number of strokes, a preset distance, a preset time or a preset work-level, and can control whether the display unit 118 should indicate progress by showing time elapsed since the beginning of the session, time remaining, distance elapsed or remaining, strokes elapsed or remaining, work expended or required, etc. Also, if any switch 120, 122 and 124 is found to be operated, a counter TIME-OUT is cleared.

At step 514, the program checks the ACCEPT flag, and only if it is set, proceeds to step 516. Step 516 is a calibration routine shown in more detail in Figure 5b, and causes the calculation of the value LOAD, and operates an indicator on the display unit 118 which indicates whether or not the machine is yet calibrated. Here, the term "calibrated" merely means that the machine is operating in a mode in which resistance control and/or indications of work expended are achieved accurately in response to measured flywheel deceleration. If desired, further calibration to relate the indicated work expenditure to known units, such as calories, could also be carried out.

At step 518, the program checks the END-STROKE flag, and, only if it is set, proceeds to step 520. Step 520 is only reached immediately after the end of each stroke. Step 520 involves clearing the END-STROKE flag, checking the STROKE/LENGTH value and using it to calculate and indicate the number of strokes per minute on the display unit 118, calculating the average speed by dividing BAR-TOTAL by BAR-COUNT and indicating this by flashing or maintaining active the corresponding segment on the bar graph display of the display unit 118, and clearing the variables BAR-TOTAL and BAR-COUNT. The user can thus see an indication representing the average flywheel speed over the last stroke. If desired, the BAR-TOTAL and BAR-COUNT variables need not be cleared at this point, so that the average speed is measured over a greater interval, e.g. from the beginning of the current work session. Step 520 also involves displaying a value dependent on the variable WORK, if necessary after processing this variable as described below. The variable WORK is cleared at appropriate intervals, e.g. at the beginning of each work session, or possibly each time step 520 is reached, so the indicated value represents work expended during such an interval.

The program then loops back to step 512. Figure 5b shows the calibration routine of step 516 in more detail. The routine is entered at step 550, and then at step 552 the ACCEPT flag is cleared. At step 553, it is determined whether the value RATE is greater than a variable TARGET. TARGET is a value representing the desired machine resistance, and depends upon the value RANGE, i.e. the current machine setting. If RATE exceeds TARGET, the program proceeds to step 554, wherein the difference between the two variables is calculated, and a flag OVER is set. Otherwise, in step 556, the flag OVER is reset, and again the difference between RATE and TARGET is calculated.

In step 558, the program determines whether the difference between RATE and TARGET is less than a predetermined tolerance value, which again is dependent upon RANGE. If the difference is within the tolerance setting, the program proceeds to step 560. A flag IN-CAL is set, to indicate that the machine is in a state where it can be calibrated, and a correction factor is set equal to a low level. Otherwise, in step 562, the IN-CAL flag is reset, and the correction factor is set to a higher level.

In step 564, the correction factor is multiplied by the difference between RANGE and TARGET, to get a value ADJUST which is used to alter LOAD. In step 566, the flag OVER is checked, and if set, the program proceeds to step 568 where ADJUST is added to LOAD. Otherwise, the program proceeds to step 570, where ADJUST is subtracted from LOAD. Then, at step 572, the display 118 is updated in dependence upon the setting of the IN-CAL flag to indicate whether or not the machine is calibrated. The routine 516 ends at step 574.

Referring to Figure 6, each time a pulse is generated by the sensor 46, this interrupt routine starts at step 600. At step 602, the program calculates the time since the last pulse was generated. This is done by checking the contents of a hardware counter within the microprocessor (104) . The result is dependent on flywheel speed. Also in step 602, the program adds a predetermined value to a counter RUN, and resets the counter TIME-OUT. A variable DISTANCE, representing the effective distance rowed since the beginning of the current work session, is either incremented or decremented depending on the current mode of the machine as set by the switch 120.

At step 604, the program alters one or more counters forming the variable WORK, which is used to provide an indication of work performed on the machine. This can be achieved in a number of different ways:

(a) Adding a value dependent upon the current value of RATE to the variable WORK. Preferably, the value is inversely proportional to RATE. This will give a reasonable indication of work expended on the assumption that resistance is substantially independent of speed.

(b) Add to WORK a value proportional to the current speed, the value also being dependent upon the current value of RATE. Preferably the value is proportional to the current speed divided by the current value of RATE. This provides an indication of work expended on the assumption that resistance is substantially proportional to speed.

(c) Add to WORK a first value dependent solely on RATE, and a second value dependent upon both speed and RATE. This will provide a more accurate indication of work expended, based on the assumption that resistance includes an element which is proportional to speed, and a further element which is not proportional to speed.

(d) Each of alternatives (a) , (b) and (c) may be varied while disregarding the variable RATE, and then subsequently combining the stored variable WORK with RATE at a later stage, for example, after the end of the stroke in step 520 of Figure 5a.

At step 606, the current interval between flywheel pulses is compared with the previously-measured interval to determine whether or not the flywheel speed is increasing. If so, a flag PULLING is set in step 608. Otherwise, in step 610, the flag PULLING is cleared. In step 612, the variable BAR-GRAPH referred to above is calculated. This is achieved by comparing the current flywheel speed with various thresholds to determine the length of the bar to be displayed on the display unit 118 to indicate current speed.

In step 614, the flag PULLING is checked, and if it is set then in step 616 flags ARMED, SI and S2 are cleared. As will be clear, the flag ARMED indicates whether or not flywheel speed is decreasing from a threshold level above speeds SI and S2, in which case it is appropriate for flywheel deceleration to be measured. Flags SI and S2 indicate, respectively, whether or not the flywheel speed has decreased below speeds SI and S2. At step 618, the current flywheel speed is checked against the threshold level. If the current speed is higher than this threshold, the ARMED flag is set in step 620.

At step 622, the ARMED flag is checked. Only if it is set, the program proceeds to set 624. This is the first of a number of steps carried out as part of the process for measuring flywheel deceleration. Step 624 checks whether the speed has decreased below SI, and if so, SI is set in step 626. Similarly, flag S2 is set in step 630 if the speed has been found in step 628 to have decreased below S2. In step 632, the speed is checked against a lower threshold, which is below S2, and if the speed has dropped below this threshold, the ACCEPT flag referred to above is set in step 634. In step 636, the program checks that the ARMED, SI, S2 and ACCEPT flags are all set. If so, the program proceeds to step 638. Thus, this stage is reached only after the flywheel speed has dropped from the upper threshold to the lower threshold. At step 638, the value RATE is set equal to CAL-COUNT, and the variable CAL-COUNT is set equal to zero. As will be explained, CAL-COUNT represents the time interval between the flywheel speed decreasing from SI to S2. At step 638, also, the ARMED, SI and S2 flags are cleared. Also, if desired, a value dependent upon RATE, and preferably inversely proportional to RATE, is displayed to indicate the actual current resistance being generated by the machine.

The interrupt routine ends at step 640. Referring to Figure 7, the timer-controlled interrupt routine starts at step 700. At step 702, a timer representing elapsed time is incremented and the variable TIME-OUT is increased. At step 704 TIME-OUT is checked against a predetermined limit. If it has exceeded this limit, this means that a predetermined time has elapsed without any switches having been operated and without any pulses having been generated by the sensor 46. Accordingly, at step 706, the microprocessor 104 operates the control circuit 134 to switch off power. At step 708 the variable RUN is decremented, and then at step 710 it is checked against a predetermined value. The value run represents the number of pulses generated by the sensor 46 within the current working session. Assuming that it exceeds the predetermined value, the program proceeds to step 712, wherein the value LOAD is caused to be delivered to the digital to analog converter 110. Otherwise, in step 714, a value zero is delivered to the digital to analog converter. This is to ensure that power is delivered to the alternator only after it has been detected that the machine is actually being used.

At step 716, the flag SI is checked. If it is set, but it is found at step 718 that S2 is not yet set, then the variable CAL-COUNT is incremented at step 720.

At step 722, the value BAR-GRAPH is added to BAR-TOTAL, and the value BAR-COUNT is incremented.

Step 724 is shown in broken lines to indicate that it is an alternative to above described step 604 in Figure 6. Step 724 can be performed as an alternative means of deriving the value WORK representing energy expended upon the machine. To achieve this, the variable WORK is incremented by an amount which is proportional to speed, as calculated by the interrupt routine in Figure 6, or proportional to the square of speed, or having components which are proportional respectively to speed and the square of speed. In addition, the value added to WORK can be dependent upon RATE, or alternatively, the value WORK can be modified in accordance with RATE prior to display, for example, in step 520. In effect, this represents the step of deriving the amount of work expended by integrating the calculated power with respect to time. On the other hand, step 604 represents the calculation of work by integrating calculated force with respect to distance.

Instead of using the variable RATE in calculating the amount of work expended, the variable RANGE (i.e. the current machine setting) could be used.

If desired, a value dependent upon the calculated speed and RATE can be displayed, e.g. at step 724, to give an indication of the current power being expended on the machine.

At step 726 the flag PULLING is checked. If it is set, then at step 728, the END-STROKE flag is checked. If END-STROKE is not yet set, this means that the pulling stroke has just terminated. Accordingly, at step 730, the END-STROKE flag is set. Also, at this step, the variable STROKE-LENGTH is set equal to STROKE-COUNT, and STROKE-COUNT is set equal to zero. STROKE-COUNT is a counter which is incremented at step 732 each time the interrupt routine of Figure 7 is executed, to count time intervals from the end of one stroke until the end of the next stroke. If at step 726 the flag PULLING was found not be set, then the END-STROKE flag is reset at step 734.

At step 736 a timer which counts half-seconds is checked, so that a routine 738 is executed only at half-second intervals. This routine involves altering various time displays according to the current mode of the machine. Similarly, the program loops from step 740 to step 742 every 80 mS. Step 742 carries out a number of routines, including causing flashing of selected segments of the display unit 118 , debouncing of switch presses, etc. At step 744 the signals delivered to the display driver 116 are updated, and a report of the status of the machine is outputted on a serial communication line (not shown) .

The interrupt routine ends at step 746. In an alternative embodiment, the deceleration of the flywheel is measured over a plurality of different speed ranges, so that more accurate results can be achieved. Thus, in Figure 6, the broken line leading to the step 632 indicates that there could be more steps similar to 628 and 630 for checking further speed thresholds S3, S4, etc. The value RATE would then be replaced by an array RATE(N) , giving different measured deceleration values for different speed ranges. The routines which use the value RATE, such as steps 553, 604 and 724 would instead look up the appropriate value in the array RATE(N) using the current speed.

By measuring deceleration at different speeds, a fairly accurate determination of the relationship between resistance and speed is obtained. If desired, this could be used to enable the control of resistance in accordance with more than one variable (e.g. in accordance with both measured resistance and speed) .

Indeed, the target value used in step 553 may be, instead of a constant, a value which depends upon a number of factors, for example, speed. In this way, resistance is controlled in a variable manner throughout the stroke so as to provide a desired "feel". There may be an alterable program to determine how the TARGET value changes throughout the stroke.

For more accurate results, it may be desirable for the deceleration to be measured at speeds in excess of those normally encountered during operation by the user. For this purpose, a motor may be provided for driving the flywheel at such speeds. This is preferably done only when the user gives the machine a command to enter a calibration mode.

In the above arrangement, the circuit is arranged so that the flywheel speed monitoring occurs in between every stroke, assuming that the flywheel speed decreases over the appropriate range. However, this is not essential, especially if the signal indicative of resistive forces is intended merely to provide an indication of work done, rather than to control the alternator. One alternative would be for the measuring operation to be carried out only when commanded by the user, for which purpose a switch may be provided. Thus, the user could operate the switch at any time during a session, to check on the degree of resistance currently being provided. The control circuit could use one or a few measurements made in this way, combined with a signal indicative of the number of strokes performed by the user or the number of flywheel rotations, to generate a signal indicative of the total amount of work carried out during the current session. This modification may be particularly useful in machines other than rowing machines. For example, the invention could be applied to an exercise bicycle in which the pedals are normally driven continuously. Periodically, the user may temporarily stop pedalling, so that during a "freewheeling" interval the control circuit can operate to measure the resistive forces.

There is no need for the signal representing the resistive forces to monitor variations occurring while the user is expending energy, and indeed it is not even essential for it to represent the major resistive force produced by the alternator so long as the latter is reasonably predictable. In the latter case the alternator could be switched off between strokes. The signal should however represent any forces which tend to vary from machine to machine or from time to time, so that such variations can be compensated for.

Various modifications can be made to the above arrangements. For example, the alternator could be of the type which has a rotating armature, or could be replaced by a dynamo. Instead of having a separate sensor arrangement 46, ripples in the signal applied to the alternator, or the frequency of the output therefrom, could be monitored to detect rotor speed.

Claims

1. An exercise machine having a mechanism which is driven by the user during operation of the machine, and sensing means able to determine an alteration in the speed of the mechanism in an interval between times at which it is driven by the user so as to provide a signal determined by said alteration and indicative of the degree of at least part of the resistance presented to the work performed by a user for either controlling the resistance or providing an indication to the user in response thereto.

2. An exercise machine as claimed in any preceding claim, wherein the sensing means is operable to determine the rates of alteration of speed at a plurality of different speed ranges in said interval.

3. An exercise machine as claimed in claim 1 or 2, wherein the mechanism is driven in a cyclical manner and said interval occurs between successive cycles.

4. An exercise machine as claimed in any preceding claim, wherein the mechanism is a flywheel.

5. A machine as claimed in any preceding claim, including means for processing a signal representing speed alteration in said interval with a signal dependent on speed of operation of the machine to generate a signal indicative of work expended on the machine.

6. A machine as claimed in claim 5, wherein the work signal represents a value dependent on both speed alteration in the interval and current measured speed, summed over effective distance moved by the mechanism.

7. A machine as claimed in claim 5, wherein the work signal represents a value dependent on both speed alteration in the interval and current measured speed, summed over time.

8. An exercise machine as claimed in any preceding claim, having an indicator for providing a display of work carried out on the maqhine in response to the signal indicative of resistance.

9. An exercise machine as claimed in any preceding claim, including means for altering the resistance presented to the user so as to make the sensed resistance correspond to a predetermined level.

10. An exercise machine as claimed in claim 9, wherein the predetermined level is alterable.

11. An exercise machine as claimed in any preceding claim, including an electrical machine which generates at least a substantial part of the resistance by virtue of the interaction between an exciting field and a field induced in windings during relative movement between the windings and the exciting field.

12. An exercise machine as claimed in claim 11, wherein the exciting field is of a substantially constant magnitude.

13. An exercise machine as claimed in claim 12, wherein the field is generated by one or more windings carrying a substantially constant current.

14. An exercise machine as claimed in claim 13, having means operable to control the resistance by varying said constant current.

15. An exercise machine as claimed in any preceding claim, including control means for varying the resistance in a predetermined, controlled fashion during operation of the machine.

16. An exercise machine in which the resistance to the work performed by the user is provided at least in part by an electrical machine in which the exciting field is of a substantially constant magnitude.

17. An exercise machine as claimed in claim 16, wherein the field is produced by one or more windings carrying a substantially constant current.

18. An exercise machine as claimed in any preceding claim, in the form of a rowing machine.