WO2023059246A1

WO2023059246A1 - Method of controlling operation of a vibratory roller

Info

Publication number: WO2023059246A1
Application number: PCT/SE2022/050881
Authority: WO
Inventors: Andreas Persson
Original assignee: Dynapac Compaction Equipment Ab
Priority date: 2021-10-04
Filing date: 2022-10-03
Publication date: 2023-04-13
Also published as: SE2151217A1; CN118318076A

Abstract

The present invention relates to a method of controlling operation of a vibratory roller (1) comprising a roller drum (3) and a vibratory mechanism (2). The method comprises determining a temperature of a surface to be compacted by the vibratory roller, determining a desired phase angle (Φd) based on said determined temperature and maintaining the phase angle (Φ) at, or close to, said desired phase angle (Φd) by controlling the vibration frequency of the vibratory mechanism (2).

Description

METHOD OF CONTROLLING OPERATION OF A VIBRATORY ROLLER

Technical Field of the Invention

The present invention relates to a method of controlling operation of a vibratory roller.

Background Art

Vibratory rollers are widely used to compact soil and asphalt mix e.g. in the construction of roads and buildings.

Such compaction is about rearranging soil or asphalt mix particles into a more dense state, by reducing air voids and increasing the contact areas between the particles. Vibratory compaction, in which dynamic forces are utilized, enables efficient compaction on most materials. Typically, a vibratory roller comprises eccentric weights mounted on a rotating shaft to cause a roller drum to vibrate at a certain vibration frequency. The forces from the roller drum cause pressure waves in the material, which in turn set the particles in motion to rearrange into a more dense state.

Generally, a high contact force between the drum and the material gives deeper compaction and a high amount of energy/impact creates powerful pressure waves to rearrange the particles. It is therefore desired to control the compaction process such that the contact force and the energy/impact is maximized, i.e. to emit energy into the ground in an efficient manner.

SE 543 161 illustrates a method of compacting using a vibratory roller. This method is based on the fact that the drum of a vibratory roller and the material to be compacted work together as a single oscillary system. More specifically, according to this method, the vibration frequency of a vibratory mechanism is continuously adjusted so as to drive the single oscillary system towards the natural frequency thereof for optimization of the compaction.

However, there is still a desire to further develop this method in some applications. Summary of the Invention

It is an object of the present invention to provide an improved method of controlling operation of a vibratory roller.

This and other objects that will be apparent from the following summary and description are achieved by a method according to the appended claims.

According to one aspect of the present disclosure there is provided a method of controlling operation of a vibratory roller comprising a roller drum and a vibratory mechanism, wherein the method comprises determining a temperature of a surface to be compacted by the vibratory roller, determining a desired phase angle based on said determined temperature, the phase angle being the difference in angular position between an eccentric force generated by the vibratory mechanism and the displacement of the roller drum, and maintaining the phase angle at or close to said desired phase angle by controlling the vibration frequency of the vibratory mechanism.

The drum of such a vibratory roller and the material to be compacted, e.g. asphalt mix, work together as one dynamic system. At, or close to, the natural frequency of the combined system, the drum amplitude is enhanced significantly, since energy is automatically fed to the system at the right time. This, in turn, maximizes the contact force between the drum and the ground, yielding maximized compaction and energy efficiency. However, the properties of the material to be compacted may be influenced by environmental conditions. Especially, asphalt mix properties change significantly with temperature and asphalt mix therefore need to be compacted before it cools to a certain temperature. Hence, there is a specific temperature range where viscosity permits adequate compaction. At lower temperatures, asphalt mix particles are more difficult to rearrange, and the required density is then difficult to achieve. In fact, a very high compaction effort is required to rearrange asphalt mix particles at low temperatures. Asphalt mix to be compacted thus becomes stiffer as the temperature thereof drops.

All drum and soil/asphalt mix combinations have their own unique natural frequencies. In addition, the fact that asphalt mix becomes stiffer at lower temperatures means that the natural frequency of a drum and asphalt mix system increases as the temperature of the asphalt mix drops. In order to compensate for this variation of natural frequency, the temperature of the surface to be compacted is determined and used to determine a desired phase angle. By taking the determined temperature into account in this manner, an improved and/or more efficent compaction is provided. Consequently, the number of passes needed to complete compaction of a certain area may be reduced. This has the advantage that both time and energy consumption may be saved, yet achieving a better compaction result.

In most cases, the present method allows a vibratory roller to compact at lower frequencies than known methods. This has the advantage that noise and/or vibrations exposed to an operator may be reduced and, hence, improves operator comfort. Also, it has the advantage that wear and tear of the vibratory roller may be reduced.

The method according to the present disclosure thus provides good and efficient compaction, high operator comfort, low wear and high energy efficiency in several applications, especially in asphalt mix compaction applications. Furthermore, the method requires no complicated mechanical mechanisms and/or additional control equipment, which further contribues in providing a cost-efficient method. Also, it provides for a robust method.

According to one embodiment the step of determining a temperature comprises measuring a temperature, which provides for a very accurate method. The temperature to be compacted may be measured using a temperature sensor.

According to one embodiment said desired phase angle is determined continuously, preferably every 0.1 to 1 seconds, more preferably 0.1 to 0.7 seconds and most preferably 0.1 to 0.3 seconds.

According to one embodiment the temperature is measured using an infrared sensor. This has the advantage that the temperature can be measured in a robust and reliable manner.

According to one embodiment the vibratory roller has at least two amplitude settings. According to one embodiment the vibratory roller has two and only two amplitude settings.

According to one embodiment the desired phase angle is determined as a function of the determined temperature. The desired phase angle may thus be determined using a predefined relationship between the phase angle and the temperature, e.g. by aid of a graph showing the phase angle as a function of the temperature.

According to one embodiment said vibratory roller comprises two roller drums and two vibratory mechanisms, wherein the phase angle is maintained at, or close to, said desired phase angle by controlling the vibration frequency of each of the two vibratory mechanisms.

These and other aspects of the invention will be apparent from and elucidated with reference to the claims and the embodiments described hereinafter.

Brief Description of the Drawings

The invention will now be described in more detail with reference to the appended drawings in which:

Fig. 1 illustrates a vibratory roller.

Fig. 2 illustrates a vibratory mechanism of the vibratory roller shown in Fig. 1.

Figs. 3a-b serve to illustrate the vibratory mechanism upon switching from a high amplitude setting to a low amplitude setting.

Fig. 4 is a schematic sectional view and illustrates a roller drum of a dual amplitude vibratory roller.

Fig. 5 is a schematic side view and illustrates sensors mounted on a non-rotating member of the roller drum shown in Fig. 4 and a temperature sensor mounted to a front part of the vibratory roller.

Fig. 6 is a graph used to determine a desired phase angle based on the temperature of a surface.

Fig. 7 illustrates steps of a method according to an embodiment of the present disclosure.

Detailed Description of Preferred Embodiments of the Invention Fig. 1 illustrates a vibratory roller 1 comprising two roller drums 3, a vibratory mechanism 2 mounted inside the roller drum 3 and a control unit 19. The vibratory roller 1 further comprises a temperature sensor, in the form of an infrared sensor 29, which is mounted to the front part thereof. The temperature sensor 29 is arranged to measure a temperature of a surface 31 to be compacted by the vibratory roller 1 . The temperature sensor 29 is thus arranged to measure the temperature of a surface 31 in front of the front roller drum of the vibratory roller 1 . The temperature sensor 29 is connected to the control unit 19 by a cable 33.

It is appreciated that the temperature sensor may be mounted to another part of the vibratory roller, such as e.g. the rear or middle part thereof. Also, it is appreciated that the vibratory roller may have one or more additional temperature sensors. By way of an example, the vibratory roller may be provided with two temperature sensors, one of which is arranged to measure the temperature of a surface in front of the vibratory roller, as seen in a first travel direction, and one of which is arranged to measure the temperature of a surface behind the vibratory roller, as seen in said first travel direction. In this example, a first temperature sensor measures the temperature of a surface to be compacted as it travels forwards and a second temperature sensor measures the temperature of a surface to be compacted as it travels backwards.

Fig. 2 and Figs. 3a-b illustrate the vibratory mechanism 2 of the vibratory roller 1. The vibratory mechanism 2 comprises a rotatable shaft 5 to which two identical eccentric mass assemblies 7 are mounted. The vibration mechanism 2 serves to generate an eccentric force upon rotation of the shaft 5.

Each eccentric mass assembly 7 comprises three eccentric masses 9, 11 , 13 two of which are fixed to the rotatable shaft 5 and one of which is movably mounted on the shaft 5. Each of the movable masses 11 is free to rotate relative to the fixed masses 9, 13 between a first position (Fig. 2), in which it cooperates with the two fixed masses 9, 13 upon rotation of the shaft 5 in one direction, and a second position (Fig. 3b), in which it partly balances the two fixed masses 9, 13 upon rotation of the shaft 5 in the opposite direction.

When the movable masses 11 are situated in their respective first positions, the vibratory mechanism 2 operates in a high amplitude setting and when the movable masses 11 are situated in their respective second positions, the vibratory mechanism 2 operates in a low amplitude setting.

The amplitude setting is switched from one to the other by changing the direction of rotation of the shaft 5. To this end, each of the movable masses 11 has two engagement portions 11a, 11b configured to engage a driving pin 14 secured to the two fixed masses 9, 13 so as to rotate therewith as the shaft 5 rotates in any direction. A first engagement portion 11a of each movable mass 11 is configured to engage a respective driving pin 14 when the shaft 5 is rotated in one direction and a second engagement portion 11b of each movable mass 11 is configured to engage the respective driving pin 14 when the shaft 5 is rotated in the opposite direction. By changing the direction of rotation of the shaft 5, the movable masses 11 are forced to switch from one position to the other one, as illustrated in Figs. 3a-b. Upon changing the direction of rotation of the shaft 5 the movable masses 11 are thus displaced relative to the fixed masses 9, 13 from one position to the other one. At continued rotation in the same direction, as illustrated by arrows in Fig. 3b, each of the movable masses 11 rotates together with the fixed masses 9, 13.

Hence, the vibratory mechanism 2 of the vibratory roller 1 has in this case two and only two amplitude settings in the form of a high amplitude setting (Fig. 2) and a low amplitude setting (Fig. 3b).

Now referring to Fig. 4, an accelerometer 15 is arranged vertically above the axis of rotation 6 of the roller drum 3. The accelerometer 15 is attached to a non-rotating structure 17 and is capable of measuring the vertical acceleration of the drum 3. The accelerometer 15 is connected to a control unit 19, illustrated in Fig. 5, by a cable 21. During operation of the vibratory roller the control unit 19 continuously receives an acceleration signal from the accelerometer 15. An eccentric position sensor 23 is arranged to provide a position signal when a reference point on the shaft 5 pass a certain position. The eccentric position sensor 23, which is attached to a non-rotating structure 25, is connected to the control unit 19 by a cable 27. During operation of the vibratory roller 1 the control unit 19 continuously receives a position signal from the eccentric position sensor 23.

The eccentric shaft 5 is rotatably arranged by means of roller bearings 10. A hydraulic motor 12 is arranged for rotating the shaft 5. Alternatively, another type of motor, such as e.g. an electric motor, may be used for rotating such an eccentric shaft.

By considering the roller drum 3 and the ground as a dynamic system having a characteristic resonance frequency and running the vibratory roller 1 close to the resonance frequency of the ground-drum system compaction can be improved. This gives maximum contact force and effective transfer of vibration energy into the ground, i.e. improved efficiency.

With reference to Fig. 7, a method of controlling operation of the vibratory roller 1 according to an embodiment of the present disclosure will now be described.

Before controlling operation of the vibratory roller 1 it is started at a default vibration frequency, such as e.g. 40 Hz, and with the vibratory mechanism 2 set in the low amplitude setting or in the high amplitude setting. Preferably, the vibratory mechanism 2 is set in the high amplitude setting.

In a first step S1 , the temperature of the surface 31 , e.g. an asphalt mix surface, to be compacted by the vibratory roller 1 is measured by the temperature sensor 29. The measured temperature is received by the control unit 19.

In a second step S2, a desired phase angle <t>d is determined based on the temperature measured in the first step S1 . The desired phase angle <t>d is determined as a function of the measured temperature. By way of an example, such a function is illustrated in Fig. 6.

In a third step S3, the phase angle <t> is maintained at, or close to, the desired phase angle <t>d by controlling the vibration frequency of the vibratory mechanism 2 of the vibratory roller 1 . The phase angle <t> is defined as the difference in angular position between an eccentric force generated by the vibratory mechanism 2 and the displacement of the roller drum 3.

In the third step S3, the actual phase angle is thus determined. To this end, the vertical acceleration of the roller drum 3 is measured by the accelerometer 15 situated vertically above the axis of rotation 6 of the roller drum 3. More specifically, the moment when a reference point on the shaft 5 passes a certain position is measured using the eccentric position sensor 23. The actual phase angle is determined based on signals from each of the accelerometer 15 and the eccentric position sensor 23. The phase angle is determined continuously by the control unit 19 and used as a control parameter for controlling the frequency of the vibratory mechanism 2, which provides for quick and accurate control of the vibration frequency of the vibratory roller. If the phase angle deviates from the desired phase angle, the vibration frequency is immediately adjusted by the control unit 19. Since the vibratory roller 1 already from start may work at the high amplitude setting the vibration frequency adjusts quickly to the desired phase angle, i.e. to the optimal phase angle.

The method steps S1-S3 are repeated and carried out continuously as the vibratory roller 1 is operated. Hence, as the vibratory roller 1 operates, the temperature of the surface 31 to be compacted is measured continuously. Also, as the vibratory roller 1 operates, the actual phase angle is continuously determined and the vibration frequency is continuously controlled so as to maintain the phase angle <t> at, or close, to the desired phase angle <t>d.

In this manner optimal compaction efficiency and/or energy efficiency is achieved.

The person skilled in the art realizes that the present invention by no means is limited to the embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

By way of an example, the method has been illustrated for controlling operation of a dual-amplitude vibratory roller of a certain type. It is however appreciated that the method can be used to control operation of other type of dual amplitude vibratory rollers as well as vibratory rollers having further amplitude settings.

By way of an example, it has been described that the temperature of a surface to be compacted may be measured by a temperature sensor situated in the front part of the vibratory roller. It is appreciated that the temperature of a surface to be compacted may be measured by a temperature sensor situated at any other part, such as e.g. the middle or rear part, of the vibratory roller. It is even possible that the control unit may receive information regarding the temperature of a surface to be compacted wirelessly from a temperature sensor that is not situated on the vibratory roller itself. For instance, the temperature may be measured by a temperature sensor situated on a paver and/or on an airborne device such as e.g. a drone.

By way of an example, it has been described that the temperature of a surface to be compacted is measured by an infrared sensor. It is appreciated that another type of temperature sensor, such as, e.g, a temperature sensor comprising a sensing member arranged to come into contact with the surface to be compacted, may be used instead of an infrared sensor or as a complement to an infrared sensor.

By way of an example, it has been described that the temperature of a surface to be compacted may be determined using a temperature sensor arranged to measure the temperature of a surface to be compacted. It is however appreciated that the temperature may be determined in another way, e.g. by means of calculations and/or estimations. Such calculations and/or estimations to determine an estimated temperature may be based on the temperature of hot asphalt mix before it is placed on the ground and/or the ambient air temperature and/or the ground temperature, and/or the type of asphalt mix and/or asphalt mix layer thickness and/or wind speed and/or geodata. Determining an estimated temperature using calculations and/or estimations has the advantage that the compaction pattern of an area to be compacted may be adapted such that the coldest asphalt mix within the area is always compacted first.

With reference to Fig. 5, it has been illustrated that each of two roller drums of a vibratory roller may have an accelerometer and an eccentric position sensor for determining a phase angle. It is however appreciated that only one, and then preferably a front one, of two roller drums of a vibratory roller may have an accelerometer and an eccentric position sensor.

Claims

1 . Method of controlling operation of a vibratory roller (1 ) comprising a roller drum (3) and a vibratory mechanism (2), said method comprising: determining a temperature of a surface (31 ) to be compacted by the vibratory roller; determining a desired phase angle (<t>d) as a function of said determined temperature, the phase angle (<t>) being the difference in angular position between an eccentric force generated by the vibratory mechanism (2) and the displacement of the roller drum (3) and being determined based on signals from each of an accelerometer (15) and an eccentric position sensor (23); and maintaining the phase angle (<t>) at, or close to, said desired phase angle (<t>d) by controlling the vibration frequency of the vibratory mechanism (2).

2. A method according to claim 1 , wherein the step of determining a temperature comprises measuring a temperature.

3. A method according to any one of the preceding claims, wherein said desired phase angle is determined continuously and preferably every 0.2 seconds.

4. A method according to any one of the preceding claims, wherein the temperature is measured using an infrared sensor (29).

5. A method according to any one of the preceding claims, wherein said vibratory roller (1 ) has at least two amplitude settings.

6. A method according to any one of the preceding claims, further comprising the step of adjusting the speed at which the vibratory roller is operated based on said determined temperature.

7. A method according to any one of the preceding claims, wherein said vibratory roller comprises two roller drums and two vibratory mechanisms, and wherein the phase angle (<t>) is maintained at, or close to, said desired phase angle by controlling the vibration frequency of each of the two vibratory mechanisms.