IBM buckling rubber sleeve

IBM buckling rubber sleeve
Manufacturer	IBM, Lexmark, Key Tronic, Maxi Switch, Unicomp, XAC, XSZ, Toshiba TEC
Switch type	Tactile
Sense method	Membrane
Rated lifetime	10 million

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The IBM buckling rubber sleeve is the provisional name for the tactile switch developed by IBM in the early 1990s as a quiet and low-profile alternative to IBM's membrane buckling spring switch for the IBM Model M family. As such, it has a wide association with the said family, first being employed on 1991's IBM Personal System/2 L40SX laptop and its Model M3 numeric keypad option. Then subsequently in 1992 reused for Model M4-family Space Saver Keyboards and modified for use on Model M6-family PS/Note, PS/55 Note and ThinkPad keyboard assemblies. Its use on portable computers was phased out by 1999, however, Unicomp continued to produce this switch for its Model M4-based Mighty Mouse keyboards until the late 2000s. The switch has also seen continued use with IBM's point of sale (POS) keyboards since the Models M7, M8, M9 and M11 were released in 1993^[1] and remain in production for use with Toshiba TEC's Global Commerce Solutions Model M-derived Modular POS Keyboards^[2].

Design

Concept

IBM buckling sleeves switches are membrane-driven and seemingly derive from the same patents and/or copyright shared with membrane buckling springs as their host devices often cite 1984 as the copyright date just like many buckling spring Model Ms. The sleeves are very tactile and are of medium weighting but do not feature part-way actuation as a property. Like membrane or conductive rubber dome switches, the user is required to bottom out to actuate but the experience of doing so is different to rubber dome switches and even some conceptually similar buckling rubber sleeve based switches. The key differences:

Compared to rubber dome switches, the rubber component sits externally from the assembly on top of a barrel plate and is used for providing tactility and return force for the keycap only - they play no part in direct actuation. Most non-capacitive rubber dome switches are required to play a role in bridging the connection with the sensing mechanism.
IBM sleeves are outwardly-expanding conical shaped and are sculpted so that the rubber at the top buckles to rest aside the bottom rubber instead of all 'squishing' at the bottom.
Unlike the conceptually close Mitsumi KPQ Type switches, IBM's design lacks the conductive rubber foot on the bottom of its actuation element (keycap rod or barrel slider), eliminating another possible element that could dampen a solid bottoming out feel.

Instead, a rod on the keycap or a slider in the barrel (depending on implementation) provides a solid interface to the membrane to close the circuit^[3].

Sleeve sizes

IBM buckling sleeves have been employed on a multitude of devices, in some cases requiring a specific size (or gauge, if you will) of sleeve. 5 distinct types of sleeves have been documented, although they may be subject to slightly differing rubber thickness or colour.

Models M3, M4 & M4-1

M3/M4/M4-1 type switch components

The original implementation of IBM's buckling rubber sleeve was introduced with the March 1991-launched IBM PS/2 L40SX laptop and its Model M3 numeric keypad option. This variant of the switch is actuated by a rod on the keyboards' keycaps that descend through given key positions barrel to press on the membrane. The L40SX keyboard assembly was repurposed for the IBM PS/2 CL57SX laptop and the Models M4 (without TrackPoint II) and M4-1 (with TrackPoint II) discrete keyboard. IBM Information Products Corporation originally produced the switch and the keyboards that used them, however, this production soon became Lexmark-based after the divesture of the aforementioned IBM division. Key Tronic briefly produced Model M4s shortly after Lexmark's exit from keyboard production and Unicomp finally continued producing and selling a keyboard based on them called the Mighty Mouse until 2010. During the 19 years of production and sale, the switch design remained unchanged. Another common feature of keyboards that use this original flavour of IBM buckling rubber sleeves is that the keycap mounts onto the keyboard via two clips on either side of the keyboard^[4].

Models M6 & M6-1

M6/M6-1 type switch components

The second implementation of IBM's buckling rubber sleeve was introduced as the Model M6 in October 1992 with the IBM ThinkPad 700 series. A minor update to the design, Model M6-1, was introduced in September 1993 with the IBM ThinkPad 750 series. The principal difference between the original type and this one is the change from rod actuation to barrel slider actuation. The keycaps now have a crosspoint mount, with a brown-coloured minimalistic slider (M6) or black-coloured 'filled-out' slider (M6-1) actuating the membrane. Despite this change, the sleeves themselves remain identical. M6 and M6-1 also saw much wider adoption, becoming the primary ThinkPad keyboard switch until and including the IBM RS/6000 Notebook 860 introduced in November 1996. M6 seems to have been exclusively produced by Lexmark, however, for M6-1, production was transferred to Key Tronic sometime between Q4 1995 and Q2 1996. M6s and M6-1s were also produced for a several companies unrelated to IBM or Lexmark including AST, CompuAdd, Cube Computers and Tadpole^[5], and an M6-1 based design was even employed for the Apple Newton MessagePad Keyboard model X0044^[6]. The last year observed to have an M6-1 example produced within is 1999^[7].

Models M7, M8, M9 & M11

Keyboards

IBM PS/2 L40SX Numeric Keypad Option (Model M3)
IBM Space Saver Keyboard (Model M4)^[4]
Lexmark Quiet Touch Keyboard (Model M4)^[4]
IBM Space Saver Keyboard with TrackPoint II/IBM Quiet Touch Keyboard with TrackPoint II (Model M4-1)^[4]
IBM Space Saver Numeric Keypad (Model M4/M4-1)^[4]
Lexmark Quiet Touch Numeric Keypad (Model M4)^[4]
IBM Retail POS Keyboard with Card Reader (Model M7)^[8]
IBM Retail POS Keyboard (Model M7-1)^[8]
IBM Retail POS Keyboard with Card Reader and Display (Model M8)^[8]
IBM Retail ANPOS Keyboard (Model M9)^[8]
IBM Modifiable Layout Keyboard (Model M11)^[8]
Unicomp Mighty Mouse (Model M4/M4-1)^[4]
IBM 4820 SurePoint Monitor Keypad^[9]
IBM PS/2 ANPOS Keyboard with Integrated Pointing Device^[9]
IBM CANPOS Keyboard^[9]
IBM 4613 SurePOS 100 Keyboard Assembly^[9]
IBM/Toshiba Modular ANPOS Keyboard^[2]
IBM/Toshiba Modular CANPOS Keyboard^[2]
IBM/Toshiba Modular 67-Key Keyboard^[2]
IBM/Toshiba Modular 67-Key Keyboard with LCD Display^[2]