accordance with the present invention longitudinally along the associated textile machine as an elevational reference as seen in fig1 the traveling service unit 1 is mounted on four supporting roller wheel assemblies 7 8 9 10 for rolling floor engagement to support the unit 1 for its traveling movement each of the supporting roller assemblies 7 8 includes an upstanding screw spindle 18 20 with a supporting wheel rotatably mounted to the lower end thereof and with the upstanding extent of the spindle 18 20 threadedly engaged with an annular nut mounted within the housing of the traveling service unit 1 each nut associated with the screw spindles 18 20 is drivenly associated with a respective control motor 15 16 for rotational operation of the nuts relative to the screw spindles 18 20 thereby facilitating vertical adjustment of the roller supporting assemblies 7 8 relative to the traveling service unit 1 in similar manner the supporting roller assemblies 9 10 are mounted in tandem to an undercarriage 11 to which an upstanding screw spindle 19 is affixed in threaded engagement with an associated nut mounted within the traveling service unit 1 in driven association with a control motor 17 for similar vertical adjustment of the roller assemblies 9 10 relative to the service unit 1 of course as those persons skilled in the art will readily recognize many other alternative constructions may be utilized to facilitate selective raising and lowering of the elevation of the traveling service unit 1 with respect to the reference rail 2 for example each of the.