Topre switch

Topre switch
Manufacturer	Topre Corporation
Switch type	Tactile
Actuation force	30, 35, 45, and 55 cN
Patents	US4584444 (1984)

History

Topre switches are a electrostatic capacitive non-contact keyboard switch designed by Japan's Topre Corporation.

Description from the Topre patent:

"The present invention has been made in consideration of the above situation, and has as its object to provide a keyboard switch wherein constant hysteresis can be obtained without changing the operation characteristics even if an operation value is arbitrarily set, thereby properly preventing chattering, and wherein an operator can know that the operation member has been depressed to a depth corresponding to the operation value.

According to one aspect of the present invention, there is provided a keyboard switch comprising an insulating substrate, a first electrode laid on the insulating substrate, a second electrode facing the first electrode, a dielectric disposed between the first and second electrodes, said second electrode being formed of a conical coil spring, and being positioned on the dielectric so that one end portion of the spring may be in contact with the surface of the dielectric, a capacitance between the first and second electrodes being mainly defined by the contact area between the dielectric and second electrode, a button on the other end portion of the second electrode for compressing the second electrode toward the first electrode to change the contact area when the button is depressed toward the first electrode, said capacitance varying with the change in the facing area which changes substantially in proportion to the depth of depression of the button, and a means for giving snap feeling to an operator when the button is depressed and the capacitance exceeds a given value, whereby the switch is capacitively coupled for a switching operation and the snap feeling is given to the operator when the capacitance exceeds the given value."

Construction

A Topre switch.

The switch consists of a slider in a housing over a rubber dome over a conical coiled spring over a printed circuit board. Switches are discrete components, but built as sheets.

The rubber dome provides most of the resistance and tactile feel. (Some Topre-switch keyboards also have differently weighted domes to compensate for individual finger strength, similar to the Key Tronic ErgoForce.)

When the conical spring is compressed, a capacitive sensing mechanism on the PCB senses the keypress mid-actuation. Circuitry on the PCB collects sensing data from smaller key groups and feeds it to the controller. This design also allows N-key rollover.

All stabiliser bars are inside the keyboard, often as part of each switch, connected to the slider itself. Most stabilised keys are mounted only in the centre; on many keyboards, only the spacebar needs two extra stabilising mounts on the sides.

Key feel

The Topre switch feels at first like a refined rubber dome; and then, in some ways, reminiscent of some mechanical-contact switches such as the Cherry MX Red and Alps SKCM Cream Damped. Its action is very smooth, with a tactile bump near the top of the stroke. After the bump, the resistance is almost flat, making it difficult to avoid bottoming out. The mid-stroke actuation point cannot be felt. The switch bottoms out with a distinct thock sound, and makes a similar sound when returning to its start position. Users generally report that Topre switches are quieter than most mechanical switches, and that they find the sounds pleasant.^[1]

Some Topre keys are very light. This, combined with their lack of tactile feedback, can cause inadvertent keypresses by users unaccustomed to them.^[2] This can happen especially on keyboards (e.g. RealForce) with differently weighted switches for different fingers.

Categorisation

Because the Topre switch utilizes a rubber dome, there is ongoing disagreement in the keyboard community over whether it should be considered "mechanical" or even "semi-mechanical". Some of this controversy comes from disagreement over whether this categorisation should be determined by its construction (the inclusion of a dome as well as a spring) or by some of its properties that distinguish it from conventional rubber-dome keyboards (crisp, light feel and mid-stroke actuation point).

The switch's dome does provide most of its resistance and all of its tactile feel; but unlike conventional rubber-dome keyboards, the Topre's dome does not provide any "mushy" resistance near the bottom of the stroke. Its conical spring provides only around 5 cN of actuation force and is therefore critical only for sensing keypresses.

Variations

Example Image	Description
	Standard Topre switch, available in many different weights and used in the vast majority of Topre-made keyboards.
	Purple switches used in Realforce keyboards. Originally used only in silenced Topre keyboards; however, Cooler Master also used this colour in their non-silenced Novatouch.^[3]
	Short-throw switch used in compact-layout keyboards. It was previously thought to exist only in a 55cN weight; however, this assumption was based on measurements gathered or guessed at by users. The only known cited force measurement is '40±15%' which presumably means 40 grams with a 15% margin of error.^[4]
	Two-tone switches used in the Happy Hacking Keyboard Professional (Type-S pictured). The main housing is moulded onto the plastic. Only the plunger can be removed, compared to the standard Realforce switch, which can be removed completely from the mounting plate.
	Second revision of the Topre keychain switch, provided at promotional Realforce events in Japan. This version has a clear acrylic housing and a coloured keycap with ‘REALFORCE’ printed on the top. The ‘A’ symbol on the second revision is coloured red as per Topre’s standard advertising for Realforce keyboards. The first version had a clear acrylic base only. It also has a coloured keycap and ‘REALFORCE’ print on the top, without the red ‘A’ symbol.
	High set or 'Hi-Pro' switches, shown here to the left of a standard Topre switch. Used in a number of Topre keyboards including the Realforce branded 108UG, 104UG and 104UK Hi-Pro, as well as some Topre OEM data-entry keyboards such as the Juki Celavi-i, Juki DATUM, Nissho KB106DE and Hatsucoh Electronics HEKB01. All of these keyboards have tall, spherical keycaps.
	Alternate dome design used on a conductive Topre switch variant. Two keyboards are known to have this switch: the Sony BKE-2011 and the Sony BKE-2010. This design may have also been used on the Sony NWS-1200,^[5] but complete details of the product are not known. The slider design is the same as the standard Topre capacitive switch.
	Topre-made switch exclusive to the Cooler Master NovaTouch TKL. Cooler Master collaborated with Topre to produce the first Topre switch compatible with keycaps for the popular Cherry MX line of switches.

Gallery

Internal components (Capacitive switch)

A rubber dome from the switch of a heavily used Topre keyboard.
Underside of a rubber dome sheet (left) and the switch mounting plate from a Topre keyboard (right). The conic springs are still in place on the dome sheet.
Side view of the mounting plate (PCB removed) showing two switches with keycaps.
Underside view of PCBs from two keyboards: glass epoxy type (green), and paper phenol type (brown) used in older keyboards.
Contact side view. Paper phenol (left) and glass epoxy (right).
Contact side view. Glass epoxy (above) and paper phenol (below).
Switch housings from a standard Topre switch (left) and a Hi-Pro style keyboard (right) with sliders removed from both.
Switch sliders from a Hi-Pro style keyboard (left) and a standard Topre switch (right). They appear to be the same height, but the base design is slightly different.
Springs from a switch (left) and spacebar (right). The switching spring plays an essential role in switch actuation.
Screws from a Topre keyboard. Left to right: case screw, grounding screw, PCB screw (type 1), PCB screw (type 2).
Comparison of caps from a short-throw keyboard and a standard cap (far right). Note the more conventional stabiliser method used for modifiers on a short-throw keyboard.
Switch housings and sliders (short-throw versions on the right).
Underside of short-throw switch housings.
Short-throw dome sheet over a standard switch dome sheet.
Underside of two dome sheets (short-throw in lower left corner).
Side view of a mounting plate from a short-throw keyboard. Stabiliser bar mounts can be seen at the left.
Underside of mounting plate from a short-throw keyboard.
PCB from a short-throw keyboard. A standard-size spring at the top shows the size difference.
Short-throw PCB screw (left) and standard Topre PCB screw (type 2, right).
Switch housings and sliders from a silenced switch (left) and a standard switch (right).
Switch sliders from a silenced switch (left) and a standard switch (right). Note the foam o-ring on the silenced variant. The silenced variant's longer stem counters the reduced travel from the foam o-ring. Not all silenced switches have this adjustment.
Foam and plastic o-rings from a silenced switch. The plastic film faces the top of the keyboard and makes contact with the switch housing's ceiling.

Internal components (Conductive switch)

A rubber dome from the switch of a Sony BKE-2011. Conductive rubber contacts are used here instead of the standard capacitive switching in most Topre keyboards. No conic spring is required.
Top view of rubber dome.
Side view of rubber dome.
Bottom view of rubber dome, with black carbon contact pad in centre.
Cluster of switch domes from the upper right corner of the Sony BKE-2011 keyboard.
Bottom view of rubber domes. The individual domes along the middle are designed to allow the LEDs on the PCB to pass through.
PCB contact side of the membrane. Oddly, the membrane appears to be carbon-coated, which would make carbon dome pads unnecessary.
Closeup of carbon-coated pads on the membrane.
Dome contact side of the membrane.
PCB from a Sony BKE-2011 showing contact traces, LEDs and diodes.
Closeup of contact traces on the PCB.