US3713700A

US3713700A - Universal continuous boring machine

Info

Publication number: US3713700A
Application number: US00086923A
Authority: US
Inventors: M Montacie
Original assignee: BLANZY OUEST UNION INDLE
Current assignee: BLANZY OUEST UNION INDLE; UNION IND BLANZY OUEST FR
Priority date: 1969-11-04
Filing date: 1970-11-04
Publication date: 1973-01-30
Anticipated expiration: 1990-01-30
Also published as: DE2054298A1; BE757838A; ES384859A1; CH552127A; GB1333754A; SE372593B; NL173086C; NL173086B; CA952135A; FR2067460A5; SU393843A3; ZA707222B; NL7016174A; DE2054298B2

Abstract

Tools mounted on swinging arms are fixed to a rotating head which, in turn, is carried by a front casing. A rear casing is coupled to the front casing and forms a chassis through parallel longitudinal members which are fixed to the front casing and are slidably received by the rear casing permitting relative longitudinal movement between the front and rear casings. A guide carriage is slidably coupled to the ends of the parallel members which protrude rearwardly of the rear casing. The head is selectively rotated and the arms carrying the tools are oscillated by a drive mechanism carried by the rear casing. Bearing jacks carried by the guide carriage selectively fixes the carriage at a given longitudinal position, while pushing jacks carried by the carriage and acting on the front casing advances the front casing when the carriage is longitudinally stopped in fixed position by the bearing jacks.

Description

United States Patent [191 Montacie [54] UNIVERSAL CONTINUOUS BORING MACHINE [75] Inventor: Marcel Montacie, Paris, France [73] Assignee: Union lndustrielle Blanzy-Ouest,

Paris, France [22] Filed: Nov. 4, 1970 [21] Appl. No.: 86,923

[30] Foreign Application Priority Data Nov. 4, 1969 France ..6937879 [52] U.S. Cl ..299/31, 299/86 [51] Int. Cl. ..E0lg 3/04 [58] Field of Search ..299/31, 86

[56] References Cited UNITED STATES PATENTS 1,201,097 l0/l9l6 Proctor ..299/3l FOREIGN PATENTS OR APPLICATlONS 1,534,6ll 8/1969 Germany ..299/3l 1 Jan. 30, 1973 Primary Examiner-Ernest R. Purser Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT Tools mounted on swinging arms are fixed to a rotating head which, in turn, is carried by a front casing. A rear casing is coupled to the front casing and forms a chassis through parallel longitudinal members which are fixed to the front casing and are slidably received by the rear casing permitting relative longitudinal movement between the front and rear casings. A guide carriage is slidably coupled to the ends of the parallel members which protrude rearwardly of the rear casing. The head is selectively rotated and the arms carrying the, tools are oscillated by a drive mechanism carried by the rear casing. Bearing jacks carried by the guide carriage selectively fixes the carriage at a given longitudinal position, while pushing jacks carried by the carriage and acting on the front casing advances the front casing when the carriage is longitudinally stopped in fixed position by the bearing jacks.

24 Claims, 11 Drawing Figures 780 lmlllj- 85 2/1970 Germany ..299/86' PATENTED JAN 3 0 I973 SHEET 2 OF 6 FIG. 3

PATENTEDJAN30 I973 3,713,700

SHEET 301 6 FIG.5

PATENTEDJAN30 197s 3.713; 700 SHEET u 0F 6 FIG. 6

PATENTEDJAH 30 I975 SHEET 5 [IF 6 PATENTED JAN 30 I915 SHEET 6 BF 6 FIG. Ilv

UNIVERSAL CONTINUOUS BORING MACHINE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention concerns a machine used for continuous boring by means of tools mounted on swingable arms carried by a rotating head on which pressure is exerted from the rear towards the working face, and relates more particularly to a machine which can be used universally, owing to the possibilities of changing drive and structure accessories on one and the same body to permit adaptation to a wide range or working conditions.

2. Description of the Prior Art It is known that the usual boring machines with fixed cutting wheels mounted on a tool carrier and placed on a head rotating at a constant speed permit boring only of a tunnel of given diameter and that the power of the driving motors is determined more particularly by the hardness of the terrain which is being excavated, under given driving conditions.

It is also known that machines using tools with oscillatory movement such as those described in French Pat. No. 1,597,434 permit, by regulation of the amplitude of oscillation ofthe tool carrier arms, boring of tunnels of circular cross-section within a small diameter range.

SUMMARY OF THE INVENTION The object of the present invention is to make the best possible use of oscillatory movement tools with a view to providing a universal boring machine, that is to say, a machine which can accept as wide a range as possible of values of the main parameters involved in boring a tunnel, on the one hand, the excavation diameter and on the other hand the hardness of the terrain being tunnelled into. For this one and the same machine body comprising a rotating head and supporting chassis participating in anchoring to the walls and in guiding, with the object of covering a wide range of tunnel diameters, is associated with a range of sets of oscillatory arms for rapid fixing with each set of arms covering a sub-range of tunnel diameters.

Thus, for machines using tools with a freely rotating disc, for adaptation to the work required, two variables are available, the rotational speed of the head and the speed of oscillation of the arms, the composition of which on contact of the cutting wheel with the working face, describes a spiral and permits varying the pitch for adapting the boring work to the hardness of the terrain. For this, it is sufficient to modify the two kinematic drive lines by the quick changing of a corresponding part. In fact, the rotational speed of the head is defined by the diameter of the tunnel to be excavated, that is to say, by the linear speed which is not be exceeded for the tool furthest from the center. The pitch of the spiral is defined by the hardness of the terrain, taking into account the penetration of the disc depending on the pressure exerted on the head and obtained by choice of the speed of oscillatory movement of the arms.

The present invention provides a universal boring machine with a rotary head provided with tools arranged on oscillatory arms. Said head is mounted forwardly of a chassis constituted by two casings connected to one another by two parallel longitudinal rain to be excavated, by simple changing of appropriate accessories, oscillatory arms, elements of the drive line, and parts for bearing contact on the surrounding terrain.

BRIEF DESCRIPTION OF THE DRAWINGS The aims and other advantages of the present invention are brought out from the following description, associated with the drawings wherein:

FIG. 1 is a side view in elevation of a machine according to the invention.

FIG. 2 is a plan view in horizontal projection of the same machine.

FIG. 3 is a section of the drive for oscillatory movement of an arm by hydraulic jack means.

FIG. 4 is a partial longitudinal half section of the front casing supporting the mobile head.

FIG. 5 is a partial axial half section of the rear casing supporting the shaft on which the mobile head is mounted.

FIG. 6, is section, details one of the reduction gears mounted-in the front casing.

FIG. 7 is a partial longitudinal half section showing details of the mounting on the rear casing of the electrical driving motors and hydraulic motor pumps.

FIG. 8 is a partial, axial sectional view of the machine at the level of the guide carriage.

FIG. 9 is a sectional view, taken on IX IX of FIG 8.

FIG. 10 shows in elevation, a partial view of the oscillatory conveyor device for removing the excavated material.

FIG. 11 is a cross section through the machine at the level of the collecting end of the conveyor.

FIG. 12 is an elevational view of that portion of the machine shown in FIG. 1 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIGS. 1 and 2, the rotary head 1' is mounted at the end of a shaft 2, the assembly rotating in bearings car-' ried by the

casings

3 and 4 of a fixed chassis and connected to one another by two parallel and cylindrical longitudinal members 5. The longitudinal members 5 are prolonged towards the rear of the machine beyond the casing 4 to serve as a slideway for the guide carriage 6 provided with a device for bearing on the lateral wall 7 of the tunnel and for pressure on the working face 8. Finally, there is attached below the machine an oscillatory conveyor device 9 as described in the French Pat. No. 2,058,432.

In FIGS. 3 and 4, the rotary head 1 comprises a welded assembly constituted by an external sleeve 10 carrying a front plate 11, an internal sleeve 12 and an end plate 13 carrying a central hub (not shown) to which is fixed, by conical fitting on a clamping ring, the hollow shaft 2 of which the rear end is visible (FIG. 5). An intermediate plate 14 effects connection between the two sleeves and 12. Sheet metal element forming a strap (FIGS. 1 and 2) support rolling contact bearings 16 in which the shafts 17 of the elbowed arms 18 oscillate, the angle a of these arms being defined by the portion of the working face 8 allocated to each of them for sweeping movement.

The mobile head thus supports four arms permitting completely sweeping of the working face 8, the general form of which is toroidal. The external portion of the arms supports a tool 19 (FIG. 1) with a freely rotating disc, whereas the internal portion has a rolling contact bearing 20 on which is articulated, strap 21, in turn, screwed to the end of the rod 22 of the piston of a double acting jack 23 fixed by journal, ball joint and bearing on the end plate 13 thus formed with four holes for allowing the passage of the four jacks 23 driving the four arms 18 in oscillatory movement.

In FIG. 5, the hollow shaft 2 comprises at its rear portion a casing 24 carrying four double pumps 25 driven by means of a pinion system 26, by an internal annulus 27 which is itself fixed with the fixed portion of the machine.

Each jack is driven for operation by a double pump 25 and the ratio of the deliveries of the two pump bodies is in the ratio of the useful cross-sections of the two chambers of the cylinder of the said jack. The pumps operate alternately as a motor and as a brake to effect a strictly controlled movement of the displacement of the jack piston. The reversal of movement is effected by a hydraulic distributor (not shown) controlled by end-of-travel contacts arranged in the vicinity of the bearings 16 of the arms and controlled by the movement of the shaft 17 of the arm 18. The regulation of the end-of-travel contacts makes it possible to fix the end positions of each oscillatory arm and consequently its angle of sweep. The arrival of low-pressure oil from thehydraulic circuit is effected through the journal 28 by which also arrives the control current for the hydraulic distributors, by means of rings 29 supplied by wipers not shown here.

The casing 4 supports the roller bearing 30 serving to define the axis of rotation of the rotary head 1 in combination with the cylindrical roller bearing 31 (FIG. 4) carried by the front casing 3 and supporting the mobile head 1 proper. Two thrust bearings 32 and 33 deal with the forces corresponding to the pressure to be transmitted to the mobile head 1.

In FIG. 4, the front casing 3 is constituted by an internal sleeve 34, an internal sleeve 35 and two

plates

36 and 37 respectively at the front and rear. On the front plate 36 there is fixed the external race of the rolling contact bearing 31, whereas the internal race is mounted on the internal sleeve 12 of the said rotary head 1 driven in rotational movement through the agency of a reduction gear arranged within the casing 3 and whose drive output pinion acts on the internal toothed annulus 38 fixed on the external sleeve of the said head I.

The sealing-tightness, relative to excavated materal and to dust, both of the rolling contact bearings 37 and of the reduction gear and gear elements participating in the rotational driving of the head 1 is ensured by sealing elements with a tight fit 39 and 40 as described in U.S. Pat. No. 3,545,81 l. Furthermore, the stability of the machine is ensured at the front by sliding shoes 41- 7 (FIGS. 1 and 2) arranged at approximately 120 from one another and fixed to the casing 3. A jack 42 arranged vertically in the support 43 fixed to the external sleeve 34 of the casing 3 bears by means of the shoe 44 on the wall 7 of the tunnel to damp vibrations occurring during operation.

In FIG. 6, the driving of the reduction gear is effected by means of the part 45 mounted on the shaft 46 and connected to the driving shaft 47 (FIGS. 1 and 2) by means of a universal-joint coupling. Drive is taken off by means of the toothed wheel 48 mounted on the shaft 49 and acting on the annulus 38 (FIG. 4). The shaft 49 receives driving movement by means of two

intermediate shafts

50 and 51 carrying two toothed wheels each. The casing 3 thus serves as a support for four gear trains driven by four shafts 47 each provided with universal-joint couplings at their two ends.

In FIG. 7, the casing 4 supports four electric motors 52 driving the transmission shafts 47 by universal-joint transmissions 53 by way of resilient couplings (not shown) accommodated within the casing 4. The latter also acts as an oil reservoir and as a support for the motor-pump sets comprising motors 54 and pumps 55 supplying oil to the various hydraulic user circuits by way of the electro-hydraulic distributor 56 arranged at the upper portion of the casing 4. The rear portion of the casing 4 supports the fixed annulus 27 (FIG. 5) serving to drive the pumps 25, effecting the oscillation of the arms. The hydraulic connections between the pumps 25 and the jacks 23 are effected by conduits under high pressure extending through hollow shaft 2.

The two cylindrical longitudinal bearers 5 (FIG. 2) connecting the

casings

3 and 4 are symmetrically situated relative to the axis of the machine, arranged to the left and right of the latter, and prolonged towards the rear where their ends are connected to one another by a plate 57.

In FIGS. 8 and 9, the rear portions of the longitudinal members 5 serve for guiding the machine by means of the carriage 58 comprising two cylindrical tubes or slides 59 in which slide the longitudinal bearers 5 and which are connected to one another by two plates 60, each carrying in their central portion a shaft 61 the axis of which coincides with that of the machine fixed rigidly to the carriage by means of rings 62 with conical fitting portions. The support of the three bearing jacks 63 comprises an external sleeve 64 and three parts 65 with conical fit arranged at 120 from one another. They receive the ends of the rods of the pistons of the jacks 63 whose cylinder ends comprise plates 66 forming a supporting shoe or skid for bearing on the wall 7 on the tunnel. The parts 65 supporting the jacks 62 are connected to the shaft 61 by means of a spherically rounded element 67 providing a universal-joint connection between said bearing jacks 63 and the machine. The spherically rounded element 67 bears on the shaft 61 fast with the carriage 58 and on the parts 65 supporting the bearing jacks 63 through the agency of the

rings

68 and 69 respectively. Each shoe 66 supports two brackets 70 on which bear the three pressure jacks 71 whose piston rods bear on brackets 72 which are also arranged at from one another and are coupled to the casing 3.

The positioning for rotational movement about the axis of the machine between the frame of the machine and the support of the rear bearing jacks 63 is provided by a group of two double-acting jacks 73 supported by brackets 74 and 75 respectively on one of the slides 59 and on the sleeve 64. This device makes it possible on the one hand to transmit to the rock the counter-torque of the boring head; on the other hand, to ensure the stability of the machine relatively to its axis, that is to say, to maintain the cylindrical longitudinal members in a horizontal plane.

In FIGS. 10, l1, and 12 the excavated material 76 falling into the gallery is brought towards the rear by four deflectors 77 mounted on the head 1 and arranged in such a manner as to constitute the elements of a discontinuous Archimedean screw.

Then the excavated material is collected by means of the oscillatory conveyor 9 suspended on the machine by the

attachments

78a and 78b (FIG. 1). The oscillatory movement is effected by a hydraulic reduction gear and motor unit 79 comprising at its outlet end, a grooved drum 80 on which is wound a cable 81 the ends of which are attached to the shoes 41.

The alternate movement of the reduction gear and motor unit 79, obtained by means of end-of-travel reserving contacts arranged in the vicinity of the axis of oscillation of one of the attachments, carries the conveyor 9 in an alternating sweeping movement along the arc 82 arrowed at its two ends about its axis of oscillation 83 (FIG. 1); whereas, its chain 84 is driven by means of the hydraulic motor 85.

The use of the machine from a position of rest comprises making it bear on the walls of the tunnel at the rear by means of the jacks 63 and then applying pressure forwardly by means of the jacks 71, applied by the rotary head against the cutting face; whereas, the front portion of the machine slides in the gallery by means of the shoes 41 and the longitudinal members 5 slide in the slides of the guide carriage 58. The advance of the machine is effected by successive steps, each step corresponding to the useful sliding length of the longitudinal members 5 in the slides 59 of the guide carriage 58. When a step is completed, the upper jack 63 for bearing on the surrounding rock is released, the pressure jacks 71 are retracted regularly by means of the pumps 55; by allocating a pump to each of the three jacks 71 a disorderly movement about the spherically rounded element 67 is prevented. The two lower jacks 63, at the retraction of the jacks 71, slide forwards on the gallery wall.

When the rear device, that is to say, the guide carriage 58 and the jacks 63 for hearing on the surrounding terrain have been moved forwards, the upper jack 63 is again subjected to pressure and the pressure jacks 71 are subjected to pressure in order to transmit the pushing force to the mobile head 1 as soon as it is rotated; whilst the sweeping movement of the elbowed arms 18 is in synchronism with the said rotation.

Each tool then cuts in the working face a groove in the form of a spiral whose pitch is then selected in accordance with the hardness of the terrain. For this purpose, the rotational speed of the head adapted to the diameter of the tunnel being excavated having been obtained by the choice of the pinions of the input shaft 46, the changing of which is facilitated by eccentric mounting thereof in the reduction gear, the frequency of oscillation of the arms 18 is adjusted to the desired value by the choice of the driving pinions 26 of the pumps 25, the changing of the shaft to which they are fixed being facilitated by the eccentric mounting thereof. The oil necessary for driving the three pushing jacks, connected in parallel during boring, comes from a gear pump with regulatable delivery making it possible to adjust manually or automatically the speed of advance of the machine to the power absorbed by the motors 52 driving the head in rotational movement.

The guiding of the machine from the indications of an appropriate aiming or sighting system, is effected by displacing the rear of the machine, acting on the three jacks 63 fast with the carriage 58 by means of the spherically rounded element 67. This displacement of the rear of the machine causes, relatively to the fixed shoes 41 or skids, a displacement in the opposite direction of the front of the mobile head, that is to say, the boring tools.

The boring machine according to the invention has important advantages relative to known machines which can be summed up as follows: the machine can bore galleries of greatly varying diameters of between 3.50 meters and 6 meters with the body of'the machine remaining the same, only the accessories being changed. More particularly, sets of arms, sets of pinions for the drive lines, both for driving in rotational movement and for oscillatory movement, and the parts for bearing contact against the terrain are changed.

The body of the machine, assembled in the factory, does not go beyond the limits set by road or railway loading gauges and the assembly of accessories on the spot requires only very little time, so that the machine can be put into operation quickly after the arrival of the body proper at the boring site The body of the machine having a small mean cross-section leaves about it, a very considerable space permitting excavated material to be collected directly at the rear of the working face on the one hand and on the other hand permits easy movement about the machine. More particularly, in order to position supports directly behind the working face, and owing to the possibility of increasing the angle of opening of the last sweeping arm it is possible to vary the bored diameter very quickly and very simply so as to bore either a finished diameter or a rough diameter greater than the foregoing in order to take into account the thickness of concrete to be poured. For this purpose it is sufficient to regulate the end-of-travel abutments of the outer oscillatory arm to fix both the angle of oscillation and the position thereof. Since almost all the weight of the machine is situated forwardly and therefore rests on the floor of the gallery by fixed shoes, better stability is obtained and vibrations and shocks are absorbed without danger.

It will be apparent that the foregoing description is not intended to have any limiting character and that the present invention comprises all possible modifications which come within the general definition which has been given.

Thus, the tools uses may differ from cutting wheels rotating freely about their axes as mentioned in the description, but still acting on the working face with a simple or multiple spiral incision with a regulatable pitch adapted to be adjusted by modification of the ratio between the frequency of rotation of the head and the frequency of oscillation of the arms.

What is claimed is: 1. A universal boring machine comprising: chassis means comprising a front casing and a rear casing, parallel longitudinal members fixed to said front casing and slidably received by said rear casing for coupling said casings together for relative longitudinal movement, a guide carriage slidably coupled to the ends of said parallel members protruding rearwardly of said rear casing, a rotatable head carrying tools arranged on oscillatory arms carried by said front casing,

drive means carried by said rear casing for selectively rotating said head and oscillating said arms,

bearing jacks carried by said guide carriage for selectively fixing said carriage at a given longitudinal position, and

pushing jacks carried by said carriage and acting on said front casing to advance said front casing when said carriage is longitudinally stopped in fixed position by said bearing jacks,

whereby, said machine operates over a wide range of boring conditions, hole diameters and hardness of the terrain being excavated.

2. The universal boring machine according to claim 1, wherein including a plurality of pushing jacks are operatively coupled to said carriage whereby said carriage slidable on the rear portion of the longitudinal members of the chassis is used for the advancing of the body of the said machine in the forward direction under the action of the pushing jacks.

3. The universal boring machine according to claim 2, further including means for supplying pushing jacks by a single pump during the pushing phase and by individual pumps during the maneuvering phase in order to ensure regularity in their displacement.

4. The universal boring machine according to claim 2, wherein the bearing jacks are provided with slides for securing the carriage to the lateral walls of the gallery.

5. The universal boring machine according to claim 4, further comprising a ball joint interposed between the carriage and each bearing jacks to permit, by separate action on each of the said bearing jacks modification of the position of the said carriage relatively to the walls of the gallery for guiding said machine.

6. The universal boring machine according to claim 1, wherein the rotary head is mounted at the end of a hollow shaft and is driven in rotational movement between two rolling contact bearings mounted respectively within the two casings.

7. The universal boring machine according to claim 6, wherein electric motors fixed at the rear of the rear casing drive the rotary head.

8. The universal boring machine according to claim 7, wherein a transmission shaft with universal-joint coupling transmits the movement of each electric motor to a reduction gear, coupled in turn to said rotary head.

9. The universal boring machine according to claim 8, wherein each reduction gear comprises plural shaft gear trains incorporated in the front casing with a drive take-off pinion at the front end thereof.

10. The universal boring machine according to claim 9, wherein a modification of the reduction ratio is effected by means permitting changing of intermediate gear wheels of the gear train.

11. The universal boring machine according to claim 10, wherein the gear wheels to be changed are carried by an eccentrically mounted shaft to facilitate changmg.

12. The universal boring machine according to claim 9, further comprising an internally toothed annulus mounted at the rear of the rotary head and in mesh with the drive take-off pinion of each reduction gear.

13. The universal boring machine according to claim 12, further including means for situating the front rolling contact bearing, mounted on the rotary head, level with the internally toothed annulus.

14. The universal boring machine according to claim 13, wherein front rolling contact bearing, and the reduction gear are situated in a space between two sealing elements arranged with a tight fit, and isolated from the exterior.

15. The universal boring machine according to claim 6, wherein the driving means for driving the arms in oscillatory movement comprise double-acting hydraulic jacks mounted about and in the vicinity of the hollow shaft and behind the rotary head.

16. The universal boring machine according to claim 15, wherein each jack acts on that end of an elbowed arm which is near the hollow shaft.

17. The universal boring machine according to claim 15, wherein each compartment of the cylinder of a jack is supplied by a hydraulic pump through a distributor, and the ratio of the deliveries of the pumps are in the ratio of the volumes of the said compartments, with the said pumps operating alternately as a motor and as a brake.

18. The universal boring machine according to claim 17, characterized in that the two pumps of one and the same jack are mounted to be rotatable in prolongation of one another, along the rear end of the hollow shaft and at the rear of the rear rolling contact bearing thereof.

19. The universal boring machine according to claim 17, further comprising limit switches for controlling the distributors, said limit switches being arranged in the vicinity of the shaft for the oscillation of each arm and, by regulation of their position, permit giving of the desired oscillation amplitude to each arm.

20. The universal boring machine according to claim 19, wherein the control circuit of the distributors is supplied through rings arranged at the rear of the hollow shaft.

21. The universal boring machine according to claim 15, characterized in that the two pumps of one and the same jack are mounted to be rotatable in prolongation of one another, along the rear end of the hollow shaft and at the rear of the rear rolling contact bearing thereof.

22. The universal boring machine according to claim 21, further including a gear train connecting the two supply pumps of one and the same jack to a fixed toothed annulus, thus ensuring the synchronization of the oscillatory movement of the arms with the rotational movement of the head.

23. The universal boring machine according to claim 24, further comprising means for changing the gear wheels of the gear train to vary the frequency of oscillation of the arms.

24. The universal boring machine according to claim 23, wherein said means for changing the gear wheels includes a shaft which is eccentrically mounted to facilitate the changing thereof.

Claims

1. A universal boring machine comprising: chassis means comprising a front casing and a rear casing, parallel longitudinal members fixed to said front casing and slidably received by said rear casing for coupling said casings together for relative longitudinal movement, a guide carriage slidably coupled to the ends of said parallel members protruding rearwardly of said rear casing, a rotatable head carrying tools arranged on oscillatory arms carried by said front casing, drive means carried by said rear casing for selectively rotating said head and oscillating said arms, bearing jacks carried by said guide carriage for selectively fixing said carriage at a given longitudinal position, and pushing jacks carried by said carriage and acting on said front casing to advance said front casing when said carriage is longitudinally stopped in fixed position by said bearing jacks, whereby, said machine operates over a wide range of boring conditions, hole diameters and hardness of the terrain being excavated.

11. The universal boring machine according to claim 10, wherein the gear wheels to be changed are carried by an eccentrically mounted shaft to facilitate changing.