US 3711812 A
An improved drive and control system for an exercise treadmill is provided which incorporates safety features for the prevention of a start-up at high belt speed after the treadmill has been turned off, or upon the resumption of power after a power failure, and to prevent rapid acceleration of the belt to a high speed condition in the case of certain control circuit failures. Circuitry, or other means, has been included in the drive system as an interlock whereby the manual on-off switch which activates the drive motor will not be effective until the motor speed control has been reset to the zero speed position. In addition, circuitry is included to provide for shutting down the drive motor in the event of a failure or malfunction in its control circuitry which could cause an unscheduled rapid increase in the treadmill belt speed to a high speed condition.
Description (OCR text may contain errors)
United States Patent n91 Cherry  DRIVE AND CONTROL SYSTEM FOR DIAGNOSTIC AND THERAPEUTIC EXERCISE TREADMILL  Inventor: Raymond I.
 Assignee: Del Mar Engineering Laboratories, Los Angeles, Calif.
 Filed: Nov. 29, 1971 ] Appl. No.: 202,754
 US. Cl ..338/200, 272/69, 200/50 C [51 Int. Cl. ..A63b 23/06  Field of Search ..338/200, 201, 198, I72, I73;
272/69; 200/42 R, 172 R, [72 A, 50 C;
[ Jan. 16, 1973 Primary Examiner-Bernard A. Gilheany Assistant ExaminerD. A. Tone Attorney-Keith D. Beecher  ABSTRACT An improved drive and control system for an exercise treadmill is provided which incorporates safety features for the prevention of a start-up at high belt speed after the treadmill has been turned off, or upon the resumption of power after a power failure, and to prevent rapid acceleration of the belt to a high speed condition in the case of certain control circuit failures. Circuitry, or other means, has been included in the drive system as an interlock whereby the manual onoff switch which activates the drive motor will not be effective until the motor speed control has been reset to the zero speed position. ln addition, circuitry is included to provide for shutting down the drive motor in the event of a failure or malfunction in its control circuitry which could cause an unscheduled rapid increase in the treadmill belt speed to a high speed condition.
7 Claims, 6 Drawing Figures PATENTED JAN 16 I973 SHEET 1 BF 2 408.5400 Owwmm I NVENTOR. RAY/40410 I. Cmszey DRIVE AND CONTROL SYSTEM FOR DIAGNOSTIC AND THERAPEUTIC EXERCISE TREADMILL BACKGROUND OF THE INVENTION The drive and control system of the present invention may be used, for example, in conjunction with the diagnostic and therapeutic exercise treadmill described and claimed in copending application, Ser. No. 103,155, which was filed Dec. 31, 1970, in the name of Joseph A. Hesen, and which is assigned to the present assignee. However, it will become evident as the present description proceeds, that the drive and control system of the invention has general utility in conjunction with a wide variety of exercise treadmills, and the like.
As described in the aforesaid copending application, it is the usual prior art practice for electrocardiograms to be taken of patients in a resting position on a table or bed. However, it has been found that a resting patient may often produce a normal electrocardiogram, even though there is clinical or other evidence of abnormalities. It has been found, for example, that more conclusive electrocardiograms may be obtained if the patient is subjected to a continuous exercise representing a constant work load which may be graded at various time intervals. The treadmill has proven to be a suitable instrument for that, and other purposes, and clinical treadmill stress testing has become widespread as a basis for the study and diagnosis of the physical condition of patients.
An important objective of the present invention is to provide an appropriate drive and control system which renders the electric motor power driven treadmill absolutely safe, and easy to operate. For example, it is known to the art to provide a manual speed control in conjunction with the power driven treadmill, whereby the attending physician, or the patient himself, may control the treadmill belt speed from a low to a relatively high value.
It is usual in the prior art power driven treadmills to drive the treadmill belt with an alternating current electric motor, and to vary the speed of the motor over a limited range by varying the applied voltage. Some treadmills have been provided in the art with mechanical variable speed control mechanisms, and some with hydraulic drives. However, with such equipment, it is difficult to obtain a smooth control to zero speed while operating under load. An improved drive for the treadmill belt which permits a smooth speed control to zero speed is obtained by using a high-permeability permanent magnet direct-current motor, and by varying the direct-current voltage applied to the motor by an appropriate speed controller. Such a motor provides the necessary high torque at low speeds, and is capable of providing, for example, smoothly variable belt speeds in a range from -10 miles an hour.
A suitable speed controller for use in conjunction with such a direct-current motor incorporates, for example, a bridge rectifier including silicon controlled rectifiers, or the like, which are controlled so that a varying amplitude direct-current voltage may be applied to the direct-current motor for speed control. However, there is a possibility for the silicon controlled rectifiers, or other elements in such a controller to burn out or malfunction, and this can result in the controller introducing maximum direct-current voltage to the motor which, in turn, results in an unanticipated abrupt rise in the motor speed from the controlled level to a maximum level.
Such an unscheduled increase in the motor speed can be hazardous, and gives rise to the possibility of injury to the patient using the treadmill. The control system to be described incorporates appropriate circuitry which responds to an unanticipated rise in the direct-current voltage applied to the motor which could result, for example, from the aforesaid malfunction in the control circuit, and which serves to de-energize the motor and shut down the system in the presence of such a condition.
The control system to be described also includes interlocking means which may be of a mechanical or electrical nature, and which prevents the drive motor from being activated until the speed control has been set to a zero or reset position. Such an interlocking means prevents the activation of the drive motor by the main switch when the speed control is in any position other than zero. Without this feature, it would be possible for a patient to be standing on the belt, with the speed control setting at some value other than zero, and with the resulting unanticipated and rapid acceleration of the belt up to the set speed, with possible injury to the patient, when the switch is turned on.
A further feature of the electrical interlocking circuit to be described is that in the event of a power failure, or should the power cable for the treadmill be unplugged from the power main receptacle, while the treadmill is operating; the drive motor will not be energized when power is restored, unless the speed control is first reset to zero. This latter control prevents possible injury to a patient who is standing on the belt when power is restored, since it prevents the belt from rapidly accelerating to the preset speed, and requires a resetting of the system before it again becomes operational.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective representation of treadmill apparatus which may be constructed to incorporate the improved drive and control system of the invention;
FIG. 2 is a front view of a control unit for the treadmill of FIG. 1, illustrating certain indicators and controls for the treadmill;
FIG. 3 is an enlarged fragmentary perspective view of a mechanical interlock between a power switch and speed control which are included in the unit of FIG. 2;
FIG. 4 is a sectional view of a latch component of the interlock of FIG. 3, taken essentially along the line 4- 4 of FIG. 3;
FIG. 5 is a circuit diagram of an equivalent electrical interlock between the power switch and speed control of the unit of FIG. 2; and
FIG. 6 is a' circuit diagram of an overspeed protection circuit for the drive motor of the treadmill of FIG. 1.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS The treadmill shown in FIG. 1 includes an endless belt 10 riding on rollers 11 and 13 which, in turn, are mounted on appropriate bearings attached to a frame 15. The belt 10 is driven, for example, by means of a motor 12 through an appropriate drive such as a toothed belt 14. Power in the form of l lO-volt AC current from the usual mains is supplied through a connector 16 to an electric control module 18 which, in turn, is controlled by a speed control rheostat 22 in a control unit 20, to control the speed of the motor 12. The control unit 20, as described in the aforesaid copending application, may be mounted on a handle section 21 of the treadmill, for appropriate control by the patient himself, or it may be removed for remote control by the attending physician, or other attendant. When activated, the motor 12 drives the belt in the direction of the arrow, and at a speed set by the setting of the speed control 22.
As shown in FIG. 2, the speed control rheostat 22 in the control unit includes a knob which is turned, for
example, in a clockwise direction to increase the motor speed, and which is turned in a counterclockwise direction to reduce motor speed. The speed control 22 may be turned in the counterclockwise direction to a zero reset position, at which the motor speed is zero. A snap-acting toggle-type manual on-off master power switch 24 is positioned on the control unit 20 adjacent to the speed control 22, as shown in FIG. 2. A speed control indicator 25 is also mounted on the control unit, and it may be directly calibrated in miles per hour (mph).
As stated above, an important objective of the present invention is to prevent any activation of the drive motor 12 when the on-off switch 24 is turned on, unless the speed control 22 has been turned back to its zero reset position, at which the speed of the belt 10 is reduced to zero. As will be described, this objective may be achieved in accordance with the invention, either mechanically, as shown in FIGS. 3 and 4, or electrically as shown in FIG. 5.
The mechanical assembly of FIG. 3 comprises a pinion 26 which engages a rack 30 on a slide 32, the slide being held in position by bearing surfaces in bulkheads 34 and 36, such that its left-hand end will enter the area 42 in the switch button of the power switch 24 when the slide is moved to the left in FIG. 3. The pinion is attached to the shaft 28 of the speed control 22, so that rotation of the speed control 22 results in correspondingrotation of the pinion. In order to cause the left-hand end of the slide 32 to be removed completely from the area 42 of the switch button 40, so as to permit full freedom in the movement of the master switch 24 from one position to the other, the speed control 22 must be turned in the counterclockwise direction to its zero or reset position, at which position the shaft 28 turns the pinion 26 to an angular position so as to displace the slide 32 to the right in FIG. 3,'thereby removing the left-hand end of the slide from the aforesaid area 42.
With the master switch 24 in the off" position, illustrated in FIG. 3, rotation of the speed control 22 and pinion 26 in the clockwise direction from the reset position to increase the speed of the belt 10, drives the left-hand end of the slide into the area 42 and over a spring-loaded latching cam 44. The latching cam 44 is a part of the latch assembly shown in FIG. 4. As illustrated in FIG. 4, the latching cam 44 is contained in the body of the switch button 40, and in its nonnal position is caused to protrude by the force of a spring 48. The
master switch is now prevented from being switched to its on" position by the presence of the latch cam 44, so long as the left-hand end of the slide 32 is in the area 42. However, when the speed control is returned to the zero reset position, the left-hand endof the slide 32 is removed from the area 42, and the switch 24 may then be turned on by depressing the switch button 40 so as to pivot the button in a counterclockwise direction about the axis A in FIG. 3.
Should the speed control be turned while the switch 24 is in its on position, the end of the slide 32 enters the area 38 under the latching cam 44. Now, when the switch button 40 is pivoted in a clockwise direction about the axis A to its of position, the end of the slide 32 moves up the inclined surface 46 of the latching cam 44, and forces the cam into the cavity in the switch button 40 against the force of the spring 48. The left-hand end of the slide 32 then moves into the area 42, and the latching cam 44 snaps out to its outer position, thereby trapping the slide 32, and preventing the switch 24 to be returned to its on state, until the speed control 22 has been returned to zero, thereby removing the left-hand end of the slide 32 from the area 42.
The interlock between the power switch 24-and the speed control 22 can be achieved electrically, as shown by the circuit of FIG. 5. The circuit of FIG. 5 includes a normally open solenoid-operated relay switch 50 which includes a relay coil 54 connected in series with the incoming alternating-current power line. The relay switch 50 is connected, for example, to the control module 18 which supplies the direct-current power to the motor 12. In its normal state, the relay switch 50 prevents the How of alternating current to the control module 18, so that the drive motor 12 which, in turn, drives the treadmill belt 10, is deenergized. The coil 54 of the relay switch 50, which when energized closes the relay switch, is included in the circuit in series with a switch 56 The switch 56 is an integral part of the speed control 22, and is closed only when the speed control is returned to its reset position. i
As shown in FIG. 5, the master switch 24 is a twopole switch. One of the poles of the switch 24 completes the circuit to the relay coil 54, only when the switch 56 is closed, so that the relay 54 can be energized only when the speed control 22 is in its reset position. The other pole of the switch 24 serves as a holding circuit to maintain the relay coil 54 energized after the speed control is subsequently turned from its reset position and the switch 56 is open. However, when the power switch 24 is actuated to its off position, the circuit cannot be energized until the speed control 22 has again been turned to the reset position to close the switch 56. Also, if power is lost for any reason, such as a power failure, or the power cable becoming unplugged, the speed control 22 must be turned back to reset" before the motor 12 can again be activated.
It is clear, therefore, that the speed control 22 must be returned to its reset" position before any belt speed can be resumed. In this way, the belt 10 of the treadmill can be started only after the speed control 22 has been turned back to the zero speed condition of the belt.
As mentioned above, the circuit of FIG. 6 shows the drive system for the motor 12, and it includes a safety circuit for preventing overspeed of the belt of the treadmill due to a failure in the control circuit of the motor 12.
In the circuit of FIG. 6, the control module 18 includes a rectifier power supply 19 which is energized from the alternating-current power source when the relay switch S0 is closed. The rectifier 19 develops the direct-current voltage for the motor 12, and the amplitude of this voltage is controlled so as to control the speed of the motor. For example, the rectifier power supply 19 may include a usual bridge rectifier which incorporates silicon controlled rectifiers in two of its arms. The direct-current voltage supplied to the motor 12 from the rectifier power supply 19 may be in the form of unfiltered, partial half-waves which, in turn, are controlled by the setting of the speed control 22 which, in turn, controls the silicon controlled rectifiers in the bridge network. Such variable controlled rectifier power supplies are known. However, should a silicon controlled rectifier, or other element in the power supply malfunction, an unscheduled and abrupt rise to maximum direct-current output could result, and this could result in an unexpected rapid acceleration of the motor 12 from its set speed to a maximum speed, with possible injury to the person using the treadmill. For that reason, a safety circuit designated 62 is incorporated into the control module, which will now be described.
The direct-current output from the rectifier 19 is connected to a potentiometer R4A which is included in the speed control 22, and which has a movable element connected to the base of a PNP transistor Q1. The collector of the transistor O1 is connected to the negative output terminal of the power supply 19, and the emitter is connected to the cathode of a diode CR1. The anode of the diode CR1 is connected through the coil of a relay K1, through a further diode CR2, and through a resistor R3 to one terminal of the motor 12. The positive terminal of the power supply 19 is directly connected to the other terminal of the motor 12. The speed control 22 includes a further potentiometer R413 which moves in unison with the potentiometer R4A, and which is connected by way of terminals P1, P2 and P3 to the rectifier power supply 19. The potentiometer R4A serves to control the timing of the firing of the aforesaid silicon controlled rectifiers, and thereby controls the effective amplitude of the direct-current voltage applied to the motor 12, in a manner known to the art.
A resistor R1 and capacitor C1 are connected from the junction of the diode CR1 and relay coil K1 to the positive terminal of the power supply 19, and a resistor R2 and capacitor C2 are connected from the junction of the diode CR2 and resistor R3 to the aforesaid positive terminal. The relay K1 has a normally closed contact in circuit with the energizing coil 54 of the power switch 50.
The setting of the potentiometer R4A provides a reference voltage at the base of a PNP transistor Q1. The transistor 01 is connected as an emitter follower, the emitter of which being connected through a diode CR1 to a resistor R1. The collector of the transistor Q1 is connected to the negative terminal of the power supply 64, whereas the resistor R1 is connected to the positive terminal. The resistor R1 is shunted by a capacitor C1. The diode CR1, resistor R1 and capacitor C1 are all connected to the other side of the energizing coil of the relay Kl.
The setting of the potentiometer R4A provides a reference voltage at the base of the emitter follower transistor Q1, and this results in a negative reference voltage across the resistor R1 in the emitter circuit of the transistor. This voltage is stored in the capacitor C1 for a period of time sufficientto permit the voltage lag of the motor 12 to equalize any change in the field current, when the potentiometer R4B section of the speed control is changed rapidly for a reduced belt speed. This storage across the capacitor C1 is necessary to prevent operation of the relay K1, with a resulting full shutdown of the system, when the speed control 22 is rapidly turned in the reduce speed direction. The voltage stored by the capacitor C1 provides a reference voltage for the relay Kl.
The relay K1 is a conventional l2-volt relay, for example, which typically operates when 6 volts is placed across the coil or across its energizing coil, or when the current in its energizing coil in either direction exceeds a minimum value. The relay K1, therefore, acts as a dif ferential switch, and opens the circuit of the energizing coil 54 of the relay switch 50 to shut down the system whenever the voltage differential across the capacitor C1 and resistor R2 exceeds a predetermined level. When the relay coil 54 is energized, the motor 12 cannot again be energized until the speed control 22 is returned to the reset position to close the switch 56.
Therefore, if, for any reason, the voltage introduced to the motor 12 by the control module 18, and which appears across the terminals B1 and B2, exceeds by a predetennined amount the reference voltage established by the setting of the speed control 22, the relay K1 is activated to shut down the system, thereby preventing an unexpected acceleration of the motor 12. Since the shut down operation is desired only where the motor voltage materially exceeds the reference voltage, the diode CR2 is included in the circuit to prohibit any excitation of the relay Kl except when the motor voltage exceeds the reference voltage, and not vice versa. In this way, inadvertent shut down of the system is obviated, for any condition except when the motor voltage 12 rises above the reference voltage so as to indicate the existence of a runaway condition.
The drive circuit of FIG. 6 causes the treadmill to continue to operate satisfactorily so long as the motor and reference voltages are in balance. However, the safety circuit 62 in the drive circuit constantly compares the reference voltage and the motor voltage, so that any failure, for example, in the control module 18, whereby the direct current output voltage to the motor 12 increases beyond a predetermined amount, causes a flow of current in the differential relay K1. This, in turn, causes the relay K1 to be activated to open the circuit of the energizing coil 54 of the relay switch 50. As mentioned above, with the coil 54 deenergized, the relay switch 50 reverts to its normally open position thereby interrupting the flow of alternating current to the control unit 18, and effectively arresting the motion of the treadmill belt 10. The response to such an unbalance beyond a predetermined amount between the reference voltage and the motor voltage is almost instantaneous and the shut down of the treadmill is accomplished without the patient sensing any particular increase in belt speed.
The invention provides, therefore, an improved drive and control system for an exercise treadmill, and one which incorporates safety features, so that the use of the treadmill, and especially for therapeutic purposes, is safe and foolproof.
While particular embodiments of the invention have been shown and described, modifications may be made. It is intended in the following claims to cover all modifications which fall within the spirit and scope of the invention.
What is claimed is:
1. In an exercise treadmill having an endless belt and an electric drive motor for the belt, a drive and control system for said motor including: an input circuit adapted to be connected to a source of electrical energy; a control circuit connected to said input circuit and responsive to electrical energy from said source for introducing control energy to said drive motor; a manually adjustable speed control for controlling the speed of said motor; an electric switch for controlling the activation of said motor; and interlocking means intercoupling said speed control and said electric switch to prevent said motor from being activated until said speed control is adjusted to a particular position.
2. The combination defined in claim 1, in which said speed control comprises potentiometer means included in said control circuit, and said electric switch is interconnected between said input circuit and said control circuit, said interlocking means preventing said control circuit from being energized until said potentiometer means is adjusted to a particular position corresponding to zero speed of the motor.
3. The combination defined in claim 2, in which said electric switch includes a manually movable button member having a slot therein, and which includes a slide member mechanically coupled to said potentiometer means and movable into said slot to prevent actuation of said switch when said potentiometer means is turned away from a position corresponding to zero speed of said motor.
4. The combination defined in claim 3, and which includes a spring-loaded latch mounted on said button member to cause said button member to latch with said slide member when said switch is actuated to its off position during a time when said potentiometer means is turned away from its aforesaid zero speed position.
5. The combination defined in claim 2, and which includes a relay switch in circuit with said input circuit to disconnect said input circuit from said source of electrical energy; and a second switch in circuit with said relay switch and mechanically coupled to said potentiometer'means to cause said relay switch to disconnect said inputcircuit from said source of electrical energy whenever said potentiometer means is moved from a position representing zero speed of said motor.
6. The combination defined in claim 1, and which includes circuitry connected to said control circuit for disconnecting said input circuit from said source of electrical energy whenever the electrical control energy introduced to said drive motor by said control circuit exceeds a particular reference level.
7. The combination defined in claim 6, in which said circuitry includes variable potentiometer means included in said speed control, a source of reference potential connected to said variable potentiometer means to establish different reference potential levels for different settings of said potentiometer means, a differential relay circuit connected to said source of reference potential, and a second circuit for introducing a second potential to said differential relay representing the potential introduced to said motor for any particular setting of said potentiometer means, said relay responding to a predetermined differential between said reference potential and said second potential to disconnect said input circuit from said source of electrical energy.