FIELD OF THE INVENTION

The invention is related to a DC motor based resistance unit for exercise equipment. BACKGROUND OF THE INVENTION

It is per se known to realise a resistance unit for exercise equipment by means of a DC motor generating a torque against the force producing by a user. This solution may be used also for realising a particularly compact resistance unit and a training device especially for home use. This kind of solution is presented for example in FI 127552B.

Only the necessary control electronics may be included in the resistance unit and the control data be brought to the device via a wireless connection from a smartphone or a tablet computer, for example. In this way the training device may be made inexpensive as for purchase costs and also operating costs.

In particular, the conventional use of a compact training device for home use is such that the resistor unit develops by means of the control set counterforce to the operator's traction or pushing motion, and, upon its termination retracts e.g. a handle with which the movement is performed to its starting position by rewinding the wire connected to it with a suitable small force, after which the training movement may be repeated.

During the pulling or pushing training motion, the motor acts as a DC generator, i.e., when resisting the movement with the force set develops a current that can be used, for example, to charge the battery of the resistance unit. During the return movement, the motor develops a force corresponding to the current fed to it returning the training device to the starting position.

The requirements for the operation and control of the resistance unit increase as a trainee wants to use the exercise device for carrying out exercises in which the resistor unit is first directed, for example, to produce a 10 kg counterforce for a training movement in one direction and then, for example, to generate a movement in the opposite direction with the force of 20 kg, where the exercise is to resist movement with muscle strength. The third form of exercise is isometric muscle work, in which the muscle-tendon complex to be trained is held in place.

In the first case, where the motion is carried out by exceeding the counterforce with muscle strength, concentric muscle work is concerned, and in the latter case, where the movement generated by a greater force is opposed with muscle strength, eccentric muscle work is concerned. Eccentric training is currently considered to be of great importance in both sports and rehabilitation, but all the movement exercises are needed to achieve a good outcome. In the realisation of the movements, the possibility to quickly change and adjust the loads at different stages of training cycles is an essential question.

Figure 1 schematically illustrates a basic solution commonly used for DC motor control. Power supply to a motor 1 is controlled by a control unit 2 applying pulse width modulation (PWM). Power adjustment takes place so that the current fed to the motor is quickly switched on and off several thousand times per second, and the adjustment is made by changing the ratio of "on" and "off periods. The greater the length of the "on" period relative to the length of the "off period is in a pulse, the greater the power of the motor is. The switching frequency is constant and typically 1 to 20 kHz.

The electric motor is an inductive load. The motor has a coil, and when the current passes through the coil, the energy is stored in the magnetic field of the coil. The stored energy is discharged as a voltage peak. The voltage peak occurs when the state of the PWM signal is changed between "on" and "off states. Without any protection, the voltage peaks would probably break the PWM control unit. As shown in Figure 1, a conventional and often sufficient solution to protect the control unit is a diode 3 in parallel with the motor 1. This protection mode works when the force generated by the motor is parallel with the motion. Instead, it does not work if the direction of the motion is reversed because the protective diode will brake the movement.

The situation thus becomes quite different when the direction of the exercise movement is varied in relation to the force generated by the motor and when the force in certain phases is rapidly increased or reduced and converted from the braking force to the traction force or vice versa. In such situations, the motor produces a variety of interferences, which very soon lead to failure and malfunction of the control electronics.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a solution that enables the as such advantageous use of a DC motor provided with a control applying pulse width modulation in a compact exercise equipment, which can be used to perform a variety of motion exercises for example so that motions in two directions when the force affects in one direction are included.

To achieve this purpose, a resistance unit for exercise equipment according to the invention comprising a DC motor and its control unit applying pulse width modulation, is characterised in that which is defined in the characterising part of the independent claim 1 of the appended claims. Other claims define various embodiments of the invention.

The solution according to the invention makes it possible to adjust the eccentric force in the exercise equipment as desired before a series of motions, regardless of the concentric force. On the other hand, this is achieved by a force generation system in which the resistance is produced by an electric motor and is electrically controlled based on control values and sensor data.

The resistance unit according to the invention makes it possible to realise both a compact and simple and a versatile and intelligent home use exercise equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and some embodiments thereof will now be explained in more detail with reference to the accompanying drawings, in which:

Fig. 1 presents a prior art solution for controlling a DC motor; and

Fig. 2 presents an example of the solution according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the exemplary solution shown in Fig. 2, a protective circuit arrangement 4 is connected in parallel with the DC motor 1 controlled by the control unit 2 applying pulse width modulation, the function of the protective circuit arrangement being to filter out various electrical interferences generated by the motor operation between the input and output terminals of the motor and the control unit 2, which interferences are harmful to the control unit and its operation and could quickly lead to failure and inactivity of the control electronics. The protective circuit arrangement 4 comprises three parallel circuit portions 4A, 4B and 4C.

The circuit portion 4A comprises a resistor 5 and a capacitor 6 connected in series. The circuit portion is able to be activated in both directions and acts as a shock absorber that filters out high frequency interferences from the current circulating through the control unit 2

The circuit portion 4B is formed by a transient diode 7 which filters high-voltage and negative peaks between the output and input terminals of the control unit 1. By selecting a transient diode (a transient-voltage-suppression (TVS) diode) with appropriate operating values, a voltage is set at which it starts to let current flow through and thus filters out high voltage peaks. The transient diode is also an advantageous choice because it works very fast. Also this circuit portion must be able to be activated in both directions.

The circuit portion 4C comprises a transistor 8 connected in series with a resistor 9 and in parallel with a resistor 12, as well as a circuit portion formed by a resistor 10 and a Zener diode 11 for controlling the transistor. The circuit portion 4C is slower and resistant to high power and current. It filters out lower overvoltages while reducing heat-generating electrical power. This circuit portion is also able to be activated in both directions. It is required when the engine works as a generator, that is, when it develops a counterforce to the user's concentric motion. The circuit portion is especially needed in fast motions, where the generated current is high.

In order that the entire protection would work, the features and operation of all three circuit portions are required. Of course, the circuit portions may vary somewhat as long as the corresponding effects are realised. The components and their performance are selected according to the performance, functions and control modes of the application.

The solution according to the invention in the resistance unit of the exercise equipment enables versatile and rapid control of the force. The operation and use of the exercise equipment is arranged so that the direction of the electric current is always the same and the direction of the force varies according to the control as desired. Force can be generated, for example, according to a given force curve, in accordance with gravity or muscle power output. For example, the solution enables the use of eccentric overloading in so-called forced repetition resistance training.

The invention may vary within the scope of the accompanying claims.