This invention relates to a method of control- ing a transport means comprising a body and wheels at¬ tached to the body on both sides of the central line thereof one after another in the longitudinal direc¬ tion of the body, whereby for changing the direction of travel of the transport means at least some of the wheels are turned about vertical axes of turning through an angle with respect to the longitudinal di¬ rection of the body in such a way that rotation axes for all the wheels intersect substantially at the same vertical axis of turning, whereby the transport means turns about the axis of turning while it moves. The invention is also concerned with a transport means in¬ tended for effecting the method and comprising a body and wheels attached to the body on both sides of the central line thereof one after another in the longi- tudinal direction of the body, the wheels being turn¬ able about vertical axes of turning for changing the direction of travel of the transport means, power means for turning the wheels; and control means com¬ prising an adjusting means for controlling the power means in such a way that when the direction of travel is changed the rotation axes of the wheels intersect substantially at the same vertical axis of turning.

Heavy objects, such a machines, containers, and the like, are usually transported by means of trans- port carriages or vehicles comprising several shafts. In transport carriages, the shafts and the wheels at¬ tached thereto are positioned at one end of the car¬ riage and the moving of the carriage is controlled by a tractor means supporting the other end thereof and being turnable with respect to the carriage. When the

shafts are fixed in the same direction with respect to the carriage, some of the wheels are forced to slide along the surface of the ground in connection with turning, which makes the turning more difficult, wears down the tires and strains the apparatus. In addition, the rear end of such carriages rights itself at turns and requires from the tractor means an extra safety distance from obstacles.

Also, a transport means is known in which a number of wheels turnable independently about a ver¬ tical axis are provided under a carriage functioning as a vehicle, whereby when the direction of the car¬ riage is changed, wheels at the front and rear end thereof are turned in opposite directions so that all the wheels move along the circumferences of circles drawn about the same centre, so that the wheels do not drag along the ground. One problem with such a sol¬ ution is the control of the device in connection with parking, because it requires an equally large space at both ends for turning, and an equally large movement at both ends requires extremely accurate control in order to get the device precisely in place.

The object of the present invention is to pro¬ vide a method of controlling a transport means in such a way that the transport means is both easy to control during displacement transport and easy to park as desired, and the invention is characterized in that all the wheels of the transport means are turned about the vertical axes and that when the angle of turning of the transport means is at least more than a prede¬ termined angle, the wheels are turned with respect to each other in such a way that the position of the axis of turning in the longitudinal direction of the transport means shifts in proportion to the magnitude of the angle of turning.

The basic idea of the invention is that during the transport stage when the angles of turning are relatively small, the wheels of the transport means move along circumferences drawn about a centre of turning positioned on the side of the middle point of the transport means, and normal safety distances suf¬ fice for the steering thereof, and that at the parking stage the centre of turning of the transport means is shifted towards the rear end when the turning angle increases, whereby the front and the rear end turn along unequal arcs and the parking is easy to carry out.

The invention will be described in more detail in the attached drawings, wherein Figure 1 is a schematical top view of a trans¬ port means according to the invention,

Figure 2 is a side view of the transport means of Figure 1,

Figures 3 to 5 are top views of the embodiment of Figure 1 when driving with different angles of turning, and

Figure 6 is a schematical view of one arrange¬ ment for controlling the transport means.

Figure 1 is a top view and Figure 2 a side view of a transport means 1 comprising a body 2, paired wheels 3a to 3h positioned at the rear end of the body and being turnable about vertical axes 4a to 4h thereof. At the front end of the body 2 there is pro¬ vided a swing joint 5 by means of which the transport means 1 can be connected turnably to a separate trac¬ tor means 6. The swing joint 5 is provided with a control sensor 7 which indicates the angle between the longitudinal axis of the tractor means 6 and that of the transport means 1, that is, an angle Ot of turning. The angle of turning indicates how much the di-

rection of travel of the transport means changes over a predetermined distance, i.e., the magnitude of the angle defined between the original longitudinal direc¬ tion of the transport means and the longitudinal di- rection of the transport means after the intersection- of the central line and a line segment drawn through the centre of turning of the transport means perpendi¬ cularly to the longitudinal central line of the trans¬ port means has moved a predetermined distance. As re- ferred to in both the specification and the claims of the present application, the definition angle of turn¬ ing has the above meaning.

When the direction of travel of the transport means 1 is changed, the tractor means 6 turns, whereby the control sensor 7 indicates the angle C of turning. By means of an adjusting means 8, the structure and operation of which are described in more detail in connection with Figure 5, the wheels 3a to 3h are turned in different ways according to the magnitude of the angle ocof turning. When the angle DC of turning is small, e.g., no more than 20°, the transport means 1 is controlled, as shown in Figure 3, so that it turns about the centre 9 of turning positioned at its longi¬ tudinal midpoint, whereby both ends of the transport means 1 move along substantially the same circular arc and the control of the transport means 1 is easy in e.g. displacement drive. In this situation, a line drawn through the centre 9 of turning perpendicularly to the central line of the transport means 1, i.e., a division line 10, goes through the longitudinal mid¬ point of the transport means 1. The wheels 3a to 3h are turned about the vertical axes 4a to 4h thereof so that the rotation axis 11a to llh of each wheel goes through the centre 9 of turning similarly as a line 12 perpendicular to the longitudinal axis of the tractor

means 6 goes through the swing joint 5.

The angle Ot of turning usually exceeds 20° in parking situations, whereby it is necessary that the radius of turning of the transport means 1 is short and on the other hand it should be easy to control. Therefore the position of the centre 9 of turning in the longitudinal direction of the transport means 1 is shifted when the angle o of turning increases, in or¬ der that the controllability of the transport means 1 would be as desired.

With regard to the described transport means 1 to be transferred by means of the tractor means 6, it is preferable to shift the centre 9 of turning towards the rear end of the transport means 1 as shown in Fig- ures 4 and 5, whereby the distance of the centre 9 of turning from the rear end of the transport means 1 is the shorter the larger the angle 0 of turning is. In Figure 4, the angle OC of turning is 45°, whereby the centre 9 of turning has been shifted over a distance a towards the rear end of the transport means 1. At the same time the radii of turning of the rear and front ends of the transport means 1 have decreased, though the radii of turning of the rear end in a considerably greater degree. In Figure 3, all the wheels 3a to 3h were turned in the same direction with respect to the body 2 of the transport means 1, even though through different angles, whereas in Figure 4 the wheels 3g and 3h are already positioned in different direction with respect to the body 2 and the wheels 3e and 3f turned nearly in parallel with the body, whereby the axes 11a to llh of all the wheels 3a to 3h still intersect at the centre 9 of turning.

In Figure 5, the angle oc of turning is 70°, whereby the centre 9 of turning has shifted over a distance b farther backwards and is positioned sub-

stantially midway between the wheels 3a to 3h. The radii of turning of the front and rear end of the transport means 1 are still shorter than in Figure 4, whereas the radii of turning at the rear end have again shortened to a greater extent. Figure 1 illus¬ trates on one hand the shifting of the centre 9 of turning in the longitudinal direction of the transport means 1 and on the other hand the changing of the radii of turning according to the angle oc of turning, whereby the centre of turning moves along an arc 9' . Figure 1 also illustrates the shifting of the division line 10 with the centre 9 of turning. It appears from Figures 4 and 5 how the wheels positioned on opposite sides of the division line are turned in opposite di- rections with respect to each other in order that the axes of the wheels 3a to 3h would intersect at the centre 9 of turning.

Figure 6 shows one arrangement for the control of the wheels 3a to 3h of the transport means 1. For the sake of clarity, only components associated with the turning of the wheel 3a are shown in the figure, the connections and operation of the other wheels 3b to 3h being similar to those described. The control sensor 7 indicating the angle O of turning is con- nected via a control line 13 to the adjusting means 8, which comprises a logic unit 14 and a hydraulic unit 15 controlled by the logic unit 14. The hydraulic unit 15 is connected by means of hydraulic fluid conduits 16a and 17a to a cylinder 18a a piston rod 19a of which is by means of a lever 20a connected so as to turn the wheel 3a about its axis of turning 4 . The axis of turning 4a comprises an angle gauge 21a which indicates the angle /3 of turning of the rotation axis 11a of the wheel 3a into the normal position of the axis 11a, that is, to a position perpendicular to the

longitudinal direction of the body 2. The angle gauge 21a is by means of a feedback line 22a connected to the logic unit 14 for indicating therein the position of the wheel 3a. The arrangement operates in such a manner that when the tractor means 6 turns with respect to the transport means, the control sensor 7 indicates the angle o of turning, which information is applied through the control line 13 to the logic unit 14. On the basis of the obtained angle value, the computer of the logic unit 14 calculates for each wheel 3a to 3h the required turning angle /Λ a to /3 h, at which the rotation axes 11a to llh of all the wheels 3a to 3h intersect at the centre of turning and which connects the hydraulic unit 15 to feed hydraulic fluid into the hydraulic conduits 16 or 17 of each wheel 3a to 3h for turning the wheels 3a to 3h by means of the cylinders 18 to the calculated angles a to h. The angle gauges 4 indicate the turning angle l a to Λ h of each wheel 3a to 3h, and when connection lines 22 indicate that each wheel 3a to 3h has turned through the calculated angle, the logic unit 14 stops the turning of the wheel in question. When the angle of turning changes, the above-described operation is re- peated and, in practice, the process takes place con¬ tinuously.

The invention is not restricted to the above- described embodiments only, but it can be effected in various ways. The wheels of the transport means may be single or paired wheels and there may be several such wheels provided on the same shaft turnably about a single axis of turning. It is not necessary that the wheels should move along the same path when driving straight ahead, but successive wheels can be posi- tioned in different ways in the transverse direction

of the transport means. Even though the drawings show a solution in which several successive wheels are po¬ sitioned on the same side at one end of the transport carriage, the invention can as well be applied in a solution in which there are only two wheels in suc¬ cession. Besides a transport carriage to be drawn with a tractor means, the transport means may be an inde¬ pendent vehicle the direction of travel of which is controlled e.g. by means of a steering wheel or the like. Thereby the control system controls the turning of each wheel in such a manner as described above. In such a case, it is possible to connect the control sensor to indicate the angle of the steering wheel or a separate wheel to be controlled by means of a steering wheel. The wheels can be turned by means of any suitable power means and constructions in place of hydraulic components. The sensors indicating the angle of turning of the wheels can be left out, if the control means and the turning means are otherwise suf- ficiently accurate.