Background of the invention

[0001] The invention relates to an arrangement for measuring radial forces of a bearing, the arrangement comprising a sensor frame that is mounted adjacent to a bearing case of a device, in a space provided on the side of the action direction of the radial forces of the bearing in the bearing case such that it is exposed to radial forces of the bearing when the device is used; a measuring sensor of radial forces which is attached to the sensor frame and is located in the sensor frame substantially on a plane passing through the radial plane of the bearing or close to it; and means for transferring measuring results provided by the measuring sensor outside the sensor frame.

[0002] The arrangement concerned is intended to measure radial forces of chain wheel shaft bearing appearing in chain hoist gear systems, for instance. Particularly, in chain hoists, in which appear vibration due to angularity of a chain wheel and consequently also dynamics of bearing forces, it is possible to employ measuring data on the bearing force to control the rotating speed of a hoist motor by means of a frequency converter, for instance. Thus the dynamics of the entire hoist may be reduced significantly, and thereby the ease of use and safety will be improved in the hoist and the service life will be longer.

[0003] The principle of this arrangement is applicable as such for use in connection with other gear systems as well, and it may also be used for monitoring the state of the bearing and for detecting damage faults. The measuring data on the radial force of the bearing may also be used for rough weighing of a load to be lifted.

[0004] It is known technology to place a tubular sensor frame with a strain-gauge transducer in a round bore in a gearbox frame, which bore is provided close to the bearing case such that between the bearing case and a sensor case there will be a narrow neck, with which an outer ring of the bearing comes into contact for a short distance. A drawback with this kind of construction is that the bore for the sensor frame must be tight, so that in certain structures transmission oil will not leak between the sensor and the bore, for instance. The tight fit between the sensor frame and the gearbox frame makes it difficult to mount the sensor frame. The mounting requires substantial force, which may damage the sensor frame and the sensor. In addition, the sensor will incur prestress, which is difficult to predict and whose effect is to be removed by calibrating each sensor separately after mounting. If the fit were loose, i.e. a sliding fit, the sensor would not detect small loads at all. A further drawback with the tight fit is that different thermal expansions in the materials of the bearing, bearing case and sensor frame, at each particular time, may cause nonlinearity in the measurement result, which is difficult to compensate for.

[0005] The above-described known art is represented, i.a., by publication WO 2006/018276 A1 .

Summary of the invention

[0006] The object of the invention is to provide a new arrangement for measuring radial forces of a bearing such that the above-mentioned problems will be solved. This is achieved by the arrangement of the invention, which is mainly characterized in that an outer track of the bearing is in immediate contact with a sensor frame.

[0007] By simply leaving out the earlier neck between the bore for the sensor frame and the bearing case, it is possible to eliminate all the above- described problems.

[0008] In that case, precision and efficiency of measuring may be readily improved, for instance, such that the bore for the bearing case and the bore of the space for the sensor frame intersect, whereby in the sensor frame, at the location against the outer track of the bearing, there is provided a recess corresponding the shape of the outer track of the bearing in the intersection area of said bores. Consequently, the contacting surface area between the outer surface of the bearing and the sensor frame increases, whereby even minor radial forces or variations therein will be easily detected.

[0009] It is also particularly advantageous that the sensor frame is weakened in the area close to the measuring sensor to ensure measurable deformation in this area of the sensor frame. This weakening may be implemented in a variety of ways, as will appear in the subsequent description of the invention.

[0010] Other preferable details of the invention are disclosed in the claims and in the description of the invention. List of figures

[0011] The invention will now be described in greater detail by means of preferred embodiments, with reference to the accompanying drawings, in which:

Figure 1 is a simplified, longitudinal section view of a sensor arrangement of the invention in connection with a gearbox frame of a crane;

Figure 2 shows the sensor arrangement of Figure 1 from the inside of the gearbox frame, seen in the axial direction of the bearing;

Figure 3 shows the sensor arrangement of Figure 1 separately, the section view being the same as in Figure 1 ;

Figure 4 is a view of an end in Figure 3, which remains inside the gearbox frame, without a seal shown in Figure 3;

Figures 5 and 6 show an implementation of an alternative sensor arrangement of the invention, represented in the same way as in Figures 3 and 4;

Figures 7 and 8 show an implementation of a second, alternative sensor arrangement of the invention, also represented in the same way as in Figures 3 and 4;

Figure 9 is a longitudinal section view of the implementation of yet another sensor arrangement of the invention.

Detailed description of the invention

[0012] With reference to Figures 1 and 2, they show part of the gear system frame 1 having a bearing case 2 and a bearing 3 placed therein. A gear system shaft supported on the bearing 3 is not shown, because the structure of the gear system itself is not relevant to the invention.

[0013] On the side where the radial forces F of the bearing 3 act, i.e. in this case in the frame 1 , above the bearing 3, there is arranged a space 4, in which a sensor frame 5 is fitted. The space 4 is provided such that, when the gear system is used, the sensor frame 5 is exposed to radial forces F of the bearing 3. Reference mark G indicates reaction forces of opposite direction of the frame 1 and the sensor frame 5. To the sensor frame 5 is attached a radial force measuring sensor 6, which is located in the sensor frame 5 substantially on the plane passing through the radial plane of the bearing 3, i.e. directly in the action direction of the radial forces F. To the measuring sensor 6, in turn, is attached an electric cable 7 that runs through the sensor frame 5 outside the gear system and forwards results from the measuring sensor 6 for further processing.

[0014] The measuring sensor 6 is typically a strain-gauge transducer, which in this case receives compressive forces (cf. particularly Figure 4). Also other sufficiently sensitive sensors measuring compressive and tractive forces may be applicable. A shear force sensor is also possible, for instance, when the sensor frame part subjected to deformation is formed such that it will incur shearing stress. The sensor shown in Figures 1 to 4 is placed in a recess 8 provided at the end of the sensor frame 5.

[0015] The sensor frame 5 is, in part, mainly in the shape of a solid of revolution, and the space 4 provided therefor is thus a cylindrical bore whose diameter is defined by the diameter of the sensor frame 5 and whose central axis A and consequently also the central axis of the sensor frame 5 is parallel to the central axis B of the bearing 3.

[0016] It is essential in this structure that the outer track 9 of the bearing 3 is in immediate contact with the sensor frame 5. In this example, to achieve this the bore for the bearing case 2 and the bore of the space 4 for the sensor frame 5 intersect, whereby in the sensor frame 5, at the location against the outer track 9 of the bearing 3, there is provided a recess 10 corresponding the shape of the outer track 9 of the bearing 3 in the intersection area of said bores.

[0017] Advantageously, the material of the sensor frame 5 is the same as the material of the frame 1 surrounding it, at least around the sensor frame 5, or the properties of the material are substantially the same as those of the material of the frame 1 surrounding it, at least around the sensor frame 5. Advantageously, the coefficient of heat expansion of the material of the sensor frame 5 is at most the same as that of the material of the frame 1 surrounding it.

[0018] In order to allow the location in the sensor frame 5 that receives and measures bearing forces to undergo sufficient deformation without the remaining area of the sensor frame 5 resisting excessively said deformation, the sensor frame 5 is weakened in the area close to the measuring sensor 6. This weakening is implemented by a cavity or bore 1 1 provided inside the sensor frame 5 or by thinning 12 provided in the outer circumference of the sensor frame 5. The portion 13 of the sensor frame 5 which comes into contact with the outer track 9 of the bearing 3, is further lightened on both sides (see Figure 4) such that this portion 13 will have straight side walls 14.

[0019] At the end of the sensor frame 5 which will be against the wall 15 of the frame 1 in the space 4, i.e. in the axial direction between the surfaces, there is an elastic seal 16 that presses against the wall 15 and thus provides axial sealing, which protects the sensor 6 and its electric parts against grease and lubricants used in the gear system. On the opposite side of the sensor frame 5 there is a second seal 17 which presses, by means of an attachment flange 18 of the sensor frame 5, against the outer edge of the space 4 in the frame 1 , i.e. between the axial surfaces, preventing grease and lubricant from leaking through the gap between the sensor frame 5 and the space 4.

[0020] The sensor frame 5 with its sensors 6 is mounted either initially to the frame 1 of the gear system or only after the gear system is otherwise completely assembled. The tolerances for the sensor frame 5 and the space 4 for it are selected such that the mounting may be carried out without strong mounting forces. In practice, there is selected a sliding fit which is allowed to leave a small clearance between the sensor frame 5 and the space 4. This clearance makes sure that in the sensor frame 5 there will not be produced prestresses. On the other hand, this clearance may cause a small displacement of the bearing and the shaft end therebelow, and thereby a contact error in a cogwheel on the shaft. This error is so small, however, that it may be allowed. The clearance concerned also compensates for measuring variations resulting from possibly different coefficients of thermal expansion of the materials used in the construction (frame 1 , bearing 3, material of sensor frame 5), which variations might cause an undesirable prestress in the sensor frame 5 and thereby an erroneous force measuring result. As the bearing, it is preferable to use a bearing having a thick outer track. This is appropriate, because rolling means bypassing the sensor also produce a force on the sensor and thus extra peaks in a sensor signal that are difficult to filter out.

[0021] The sensor frame 50 shown in Figures 5 and 6 differs from the sensor frame 5 of Figures 1 to 4 only in the respect how the sensor frame 50 is weakened in the area close to the measuring sensor 6. This weakening is implemented in the sensor frame 50 by removal of material beneath it or by a recess 1 10 that extends to a considerable portion of the cross section of the sensor frame 50, beyond its centre line. The portion 130 of the sensor frame 50 which comes into contact with the outer track 9 of the bearing 3, is further lightened on both sides (see Figure 4) such that this portion 130 will be provided with lateral recesses 140. These lateral recesses may also be used in the control of conductors of the electric cable 7.

[0022] Figures 7 and 8 show a two-part sensor frame 150 comprising a main frame 151 and a contact part 152, which comes into contact with the outer track 9 of the bearing 3 and is secured to the main frame 151 with axial bolts 153. This enables the placement of the sensor 6 also between the parts 151 and 152, even though the sensor 6 is here shown placed at the outermost end of the contact part 152.

[0023] Figure 9 shows a further, possible, simple implementation of a sensor frame 250.

[0024] The above description of the invention is only intended to illustrate the basic idea of the invention. A person skilled in the art may thus vary its details within the scope of the accompanying claims. In addition, it should be noted that the radial forces of the bearing in the bearing case may also act in a direction other than above the bearing, for instance laterally, depending on the direction, in which the loading at the other end of the bearing- mounted shaft is acting. The solution of the invention may also be applicable in other projects where measuring and monitoring of desired compressive, tractive and shear forces, or the corresponding loads, are required.