The present invention refers to an apparatus, and to the relevant method, for measuring the torques transmitted through a speed variator comprised between two shafts.

BACKGROUND ART

The present invention typically applies to the non- automotive sector. Therefore, the present apparatus has been found to be particularly suitable for use in the field of industrial speed reducers, characterized by a "fixed" reduction ratio, usually of more than 1:30.

Thus, in the present application the typical speeds of rotation of the input shaft are comprised between 0 and 500 rpm.

More in particular, the present invention relates to a method for measuring the torques transmitted through a speed reducer/multiplier by simultaneously measuring the positions of two shafts.

As is known, the main systems currently used to measure instantaneous torque are based on the following principles :

1) measurement of the torque by measuring the electric power absorbed by the motor; the main drawback of such a system lies in the fact that the measurement is heavily influenced by factors of instability which can cause undesirable variations in the measurement; such factors of instability are linked to the electrical efficiency of the motor and the power dissipated in the rotating systems such as bearings and sealing rings; and

2) the use of a torque flange; the system is applied to rotating parts (drive shafts), and uses electromagnetic or radio-frequency devices, with sliding contacts, to measure the torque between two surfaces moving in relation to one another; the main drawback of such a system consists in the complexity and fragility of the integrated electronics and of the control system.

The present invention thus responds to the need to find a simpler and more economical solution for measuring the instantaneous torque transmitted by a first shaft to a second shaft through a speed variator, in particular a gear reduction unit.

DISCLOSURE OF INVENTION

Therefore, according to the present invention there are provided an apparatus and a method according to that claimed in the appended independent claims, and preferably, in any one of the claims depending directly or indirectly on said independent claims. BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the present invention, a preferred embodiment thereof will now be described, purely by way of non-limiting example and with reference to the accompanying figure which illustrates a tentative outline of the apparatus according to the present invention for the instantaneous measurement of the torque transmitted between two shafts through a speed variator.

BEST MODE FOR CARRYING OUT THE INVENTION

In the accompanying figure, denoted as a whole by reference numeral 100 is an apparatus for the measurement of the torque transmitted between two shafts (SHI), (SH2) through a speed variator (RDR) .

The apparatus 100 is one of the objects of the present invention.

Incidentally, it should be noted that, according to the present embodiment, the first shaft (SHI) is the high ^¬ speed input shaft, and the second shaft (SH2) represents the output shaft which is coupled, in a manner that is known and is not illustrated, to a device (not illustrated) which must receive or transmit a certain amount of power.

The input shaft (SHI) rotates about a first longitudinal axis of symmetry (XI) according to the direction of an arrow (Fl) ; while the output shaft (SH2), which is located downstream of said reducer (RDR) , is made to rotate about a second longitudinal axis of symmetry (X2) according to the direction of an arrow (F2) .

The axes (XI) and (X2) may or may not be aligned with one another.

The apparatus 100 for the measurement of torque comprises a first sensor (SNS1) suitable to detect the instantaneous position of the input shaft (SHI) with respect to a "first zero initial value", and a second sensor (SNS2) suitable to detect the instantaneous position of the output shaft (SH2) with respect to a "second zero initial value".

Advantageously, according to the present invention the sensors (SNS1) , (SNS2) are of an economical type, since they only need to measure angular displacements of +/- 5° . It is therefore possible to use magnetic or inductive pick-up sensors with a phonic wheel that has between 16 and 100 teeth. Nonetheless, applications with more teeth are possible.

The sensors may, inter alia, also be fitted on the inside of the reducer box and detect the passage of said gear teeth.

The signals from the two sensors (SNS1), (SNS2) are then integrated by an electronic device (CC) (electronic control unit) suitable to implement a calculation algorithm in such a way that:

Mt= (k) . (AQt) where (k) is a constant function of the materials and of the geometry of the reducer (RDR) .

Moreover, the connection between the two sensors (SNS1) , (SNS2) and the electronic device (CC) (electronic control unit) may be by means of a cable or wireless.

In other words, the principle of operation of the apparatus 100 is based on the existence of a correlation between the instantaneous angular displacement (A9t) of the shafts and the instantaneous torque (Mt) transmitted, defined by the torsional stiffness (k) of the reducer between the shafts (SHI) and (SH2) .

As already stated, the torsional stiffness (k) of a speed variator device is, above all, a function of the internal geometry of the transmission elements (shafts, gears, bearings (etc.), and of the materials used to make the various parts of the reducer.

Some values of (k) for two typical reducers, to be used purely for guidance, are provided below:

EXAMPLE 1 ) orthogonal axis reducer, 2 reduction stages, 850 Nm of transmittable nominal torque: (kl) = 8000 Nm/degree, which is the torsional stiffness referred to the output shaft;

EXAMPLE 2 ) planetary reducer, 2 reduction stages, 11000 Nm of transmittable nominal torque: (k2) = 34000 Nm/degree, which is the torsional rigidity referred to the output shaft.

In other words, when the value of the torsional stiffness (k) function is known for a given reducer (RDR) (or in general: speed variator) , the sensors (SNS1), (SNS2) simply have to measure the relative angular displacement (A9t) between the two shafts (SHI), (SH2) to know the value Mt of the torque transmitted between said two shafts instant by instant .

The system permits the determination of the instantaneous torque transmitted statically and dynamically as a function of the relative displacement which can be calculated using the data acquired by the position sensors. The measurement can be performed in both directions of rotation with variable speeds and torques .

The required level of precision of the sensors depends on the reduction (or multiplication) ratio of the reducer (multiplier) for which the transmitted torque is to be calculated. In particular, the angular resolution of the sensor on the output shaft must be proportional to the product of the angular resolution of the sensor on the input shaft and the reduction (or multiplication) ratio.

Since the reducer has a fixed reduction ratio, a "known angular displacement" is generated in the case of a system with infinite stiffness.

However, since each mechanical system has a given effective stiffness, the "incremental angular displacement" will be effective with respect to said "known angular displacement" .

Therefore, if the quota part of the "incremental angular displacement" is measured by performing a retroactive check, it is possible to calculate the displacement associated with the effective stiffness of the reducer, which will be equal to the difference between the "incremental angular displacement" and the "known angular displacement".

The system acquires the angular position of the output and input shafts with the same synchronized time intervals. The signals are processed to obtain the net difference in angular position between the input and the output shafts. Thus, as mentioned previously, the algorithm Mt= (k) (A9t) is used to calculate the torque transmitted by the reducer (or multiplier) .

The method for measuring the instantaneous torque Mt, which is a further object of the present invention, involves the following steps which are coordinated by said electronic device (CC) :

STEP 1 ) :

- detecting the position of a first shaft (SHI) : 9i(t);

detecting the position of a second shaft (SH2) : 9i(t);

STEP 2 ) :

calculating the instantaneous angular displacement (ΔΘ) between the angular position of the second shaft (SH2) and that of the first shaft (SHI); STEP 3) :

determining the recovery time of the angular clearance tO of the kinematic chain for the synchronization of the signal;

STEP 4 ) :

- calculating the instantaneous angular displacement (ΔΘ) given by the different angular position of the second shaft (SH2) and the first shaft (SHI), also taking into account the variation ratio (r) of the speed variator (RDR) ;

STEP 5) :

- calculating the torque Mt transmitted through the speed variator (RDR) using the algorithm:

Mt= (k) . (ΔΘ)

where (k) is the torsional stiffness of the speed variator (RDR) .

The main advantage of the apparatus (and of the method) described above lies in the fact that once the torsional stiffness is known for a given reducer (or multiplier) , it suffices to fit simple sensors to measure the instantaneous angular displacement (ΔΘ) between the second shaft (SH2) and the first shaft (SHI) in order to obtain (using a simple algorithm) the value of the instantaneous torque Mt transmitted through said reducer (or multiplier) . The sensors can therefore be extremely simple (for example optical sensors) and non-invasive, and their use does not involve major changes to the mechanical parts concerned (reducer/multiplier, drive shafts, etc.) .

Furthermore, the apparatus that is the ob ect of the present invention, besides being used to obtain an absolute measurement of the instantaneous torque, may also be used to obtain relative measurements; more in detail, to evaluate the percentage of torque applied with respect to a reference value, after "storing" the angular displacement relative to the reference torque.

In other words, a further object of the present invention is a method comprising a further step of relative measurement, as a percentage, of a given torque with respect to a reference torque, after "storing" the angular displacement relative to the reference torque.

The present invention achieves a "self-learning" and system calibration mechanism.

The stiffness (k) of the reducer is not known beforehand, but if the reducer is subjected to the maximum allowable mechanical load (specified in the manufacturers' technical manuals) 100% of the angular displacement can be attributed to said torque value. The stiffness (k) is determined by working backwards. Since the intermediate angular displacement values are proportional to the maximum torque value, the intermediate values of the torques transmitted can be estimated.

A further advantage of the present invention lies in the fact that the values of the torques which transit through the reducer instant by instant are used as the input data for a condition monitoring system (not illustrated) for controlling the vibrations of the reducer and the noise emitted thereby.