Improved oscillating hand tool

Abstract: The invention provides a braking system for a powered oscillating hand tool which tool comprises: (i) a housing (6) (ii) a drive unit (2) having an electric motor (4) and a drive shaft (8); (iii) a bearing (28) mounted on the drive shaft (8) and located radially eccentrically relative to the drive shaft (8), adapted to drive a second drive shaft (26); (iv) means (22) for mounting an oscillating head (24) on the second drive shaft (26) and (v) brake means (30) for providing braking between the oscillating head (24) and the housing (6). The brake means (30) comprises: (i) a reaction surface (35,46) (ii) a resilient support member (32,40) formed from a resilient material which material, under compression, provides a resultant load on the contact surface and (iii) an abrasion resistant contact layer (34,44) mounted on the support member (32,40).

Description: The present invention relates to a powered oscillating hand tool as per the preamble of claim 1. An example of such a tool is disclosed in EP-A-0 541 275. In a random orbit sander, a circular platen is driven by a drive system which comprises an eccentric bearing so that the platen can spin independently of the motor, and the platen describes a random orbit. Such sanders are in general used for the removal of relatively large quantities of material. It is known to provide braking in random orbit sanders, in which a brake which is mounted in the housing is in constant contact with the sanding platen, which brake operates in two ways. When the sander is in use, the brake acts a platen speed limiter, operating in particular to prevent scratches when the unit is placed on and taken off the work surface. Secondly, when the unit is switched off, the stop time is very much reduced. It is a disadvantage of known braking systems of this type, that they consist of a relatively complex spring and leg design which is expensive to manufacture and has to be sealed against dust ingress. DE 42 26 741 describes a grinding machine, in particular eccentric grinding machine, with an aspiration device, a grinding plate and a collar which is rigid with the housing, surrounds the grinding plate and comprises a sealing lip which rests on the grinding plate and extends from an attachment zone substantially concentric to the axis of rotation and connecting it to the collar to a support zone which is substantially concentric the axis of rotation and with which it rests on the grinding plate, characterised in that the resilient sealing lip 27 extends from its attachment zone 28 obliquely to the axis of rotation D into its supporting zone 29 and its diameter in the supporting zone 29 is smaller than the diameter in the attachment zone 28 and in that the vacuum occurring in the housing 1 during the grinding operation owing to the aspiration device 24 reduces the supporting pressure with which the resilient sealing lip 27 rests on the grind plate 12. It is an object of the present invention to provide a powered oscillating hand tool in which the above disadvantages are reduced or substantially obviated. The present invention provides a powered oscillating hand tool which tool comprises (i) a housing (ii) a drive unit having an electric motor and a first drive shaft; (iii) a bearing mounted on the first drive shaft and located radially eccentrically relative to the first drive shaft, and driving a second drive shaft; (iv) an oscillating head mounted on the second drive shaft; (v) brake means for providing braking between the oscillating head and the upper housing said brake means being constantly engaged; (vi) a reaction surface and (vii) an abrasion resistant contact layer mounted on a resilient support member characterised in that said resilient support member is in the form of a ring or one or more posts and is formed from a resilient material, one of said reaction surface and said abrasion-resistant contact layer being mounted on the upper housing and the other being mounted on the oscillating head, whereby the resilient material, under compression, provides a resultant load on the reaction surface. In a preferred embodiment of a powered hand tool according to the invention, the powered hand tool comprises a random orbit sander and the oscillating head comprises a sanding platen. The braking means may be in the form of a ring mounted on the platen or in the housing. Where the ring is mounted on the platen, the abrasion resistant contact layer is arranged to contact a corresponding fixed reaction surface mounted in the housing, suitably the outer surface of the impeller shroud. Where the ring is mounted in the housing, the abrasion resistant contact layer is arranged to contact the backing face of the platen. It is a particular advantage of the powered hand tool according to the present invention that, where the braking means is in the form of a ring, this provides a seal between the platen and the housing, which results in improved efficiency of dust extraction. The braking means may alternatively be in the form of one or more posts, each mounted either on the platen or in the housing. Where the brake means is in the form of a post or posts, the post or posts are preferably each mounted in a casing, more preferably in the housing, with the abrasion resistant contact layer or layers arranged to contact the backing (non-sanding) face of the sanding platen. Where the support member is in the form of a post mounted in a casing, the support member is preferably secured in the casing by means of an adhesive layer. The braking system of a power tool according to the invention, is a particularly suitable for use in a dual function powered oscillating hand tool of the type described in our co-pending UK Patent Application No 94.15011.7, when that tool is operating in the random orbit mode. A particularly suitable material for the abrasion resistant contact layer is polytetrafluoroethylene (PTFE) brake material. For increased abrasion resistance, fillers such as carbon powder or glass can be added to the PTFE. Particularly suitable materials for the resilient support member include natural or synthetic rubbers or synthetic foam materials such as polyethylene, polyurethane or PVC-nitrile. A heat resistant layer may be included between the resilient material and the abrasion resistant contact layer. The invention will now be further described with reference to the accompanying drawings in which: Figure 1 is a side view, partially in section, of a first embodiment of a hand tool according to the present invention and Figure 2 is a side view, partially in section, of a second embodiment of a hand tool according to the present invention. Figure 1 shows a drive unit (2) including an electric motor (4) located in an upper housing (6) and driving shaft (8). A fan (10) mounted on shaft (8) is arranged to draw air in from mouth (14) of a lower housing (16) and direct it through an extractor duct (18) to an exhaust outlet (20). A nut (22) is used to secure an oscillating head comprising a sanding platen (24) to a shaft (26) which is housed in the fan (10) by a bearing (28) which is eccentrically located radially in respect to shaft (8). As can be seen from Figure 1, the brake means (30) comprises a foam post (32) to which an abrasion resistant contact surface (34) is attached. A casing (36) to house the foam post (32) and abrasion resistant contact surface (34) is located in the upper housing (6). The foam post (32) is secured within the casing (36) by means of an adhesive layer (not shown). A reaction surface on the backing face of the sanding platen (24) is arranged to contact the abrasion resistant contact surface (34). In an alternative embodiment shown in Figure 2, a foam ring (40) is mounted on a backing face (42) of the sanding platen (24) and an abrasion resistant contact surface (44) is attached to the foam ring (40). A reaction surface (46) is provided in the housing (6) for engagement with the abrasion resistant contact surface (44). In operation, in the embodiment shown in Figure 1, as power is supplied to the motor (4), the shaft (8) is driven in rotation and drives the shaft (26) via the eccentric bearing (28). The shaft (8) is typically driven at a rotational speed of 12000 rpm, which is too fast a speed for rotation of the sanding platen (24). The brake means comprising the foam post (32) and abrasion resistant contact layer (34) is in constant contact with the reaction surface (35) on the backing face (42) of the sanding platen (24) and limits the rotational speed of the platen to an acceptable operating speed, typically around 1200 rpm, or 10% of the rotational speed of the motor. Similarly, in operation of the embodiment shown in Figure 2, as power is supplied to the motor (4), the shaft (8) is driven in rotation and drives the shaft (26) via the eccentric bearing (28). The shaft (8) is typically driven at a rotational speed of 12000 rpm, which is too fast a speed for rotation of the sanding platen (24). The brake means comprising the foam ring (40) and abrasion resistant contact layer (44) is in constant contact with the reaction surface (46) in the upper housing (6) and limits the rotational speed of the platen to an acceptable operating speed, typically around 1200 rpm, or 10% of the rotational speed of the motor.

Claims: A powered oscillating hand tool which tool comprises (i) a housing (6, 16) (ii) a drive unit (2) having an electric motor (4) and a first drive shaft (8); (iii)a bearing (28) mounted on the drive shaft (8) and located radially eccentrically relative to the first drive shaft (8), driving a second drive shaft (26); (iv) an oscillating head (24) mounted on the second drive shaft (26); (v) brake means (30) for providing braking between the oscillating head (24) and the upper housing (6) said brake means (30) being constantly engaged; (vi) a reaction surface (46) and (vii) an abrasion resistant contact layer (34,44) mounted on a resilient support member (32,40) characterised in that said resilient support member (32,40) is in the form of a ring or one or more posts and is formed from a resilient material, one of said reaction surface (46) and said abrasion-resistant contact layer (34,44) being mounted on the upper housing (6) and the other being mounted on the oscillating head (24), whereby the resilient material, under compression, provides a resultant load on the reaction surface (46). A powered oscillating hand tool according to claim 1 characterised in that the tool is a random orbit sander and the oscillating head is a sanding platen. A powered oscillating hand tool according to claim 2 characterised in that the braking means is in the form of a ring mounted on the platen. A powered oscillating hand tool according to claim 2 characterised in that the braking means is in the form of one or more posts, each mounted either on the platen or in the housing. A powered oscillating hand tool according to claim 4 characterised in that each post of the braking means is mounted in a casing. A powered oscillating hand tool according to claim 5 characterised in that each post of the braking means is mounted in a casing located in the housing. A powered oscillating hand tool according to any of claims 1 to 6 characterised in that the abrasion resistant contact layer is made from polytetrafluoroethylene (PTFE). A powered oscillating hand tool according to any of claims 1 to 7 characterised in that the resilient material is a natural or synthetic rubber or a synthetic foam material. A powered oscillating hand tool according to claim 8 characterised in that the resilient material is polyethylene, polyurethane or PVC-nitrile. A powered oscillating hand tool according to any of claims 1 to 9 characterised in that a heat resistant layer is located between the abrasion resistant contact layer and the resilient material.

Inventors: BONE DANIEL, MARTIN MICHAEL, PUGH COLIN, BONE, DANIEL, MARTIN, MICHAEL, PUGH, COLIN
Applicants: BLACK & DECKER INC, BLACK & DECKER INC.
Application year: 1995
Main classification: B24B23
IPC codes: B24B23